October 13

A Whirlpool Among the Stars

1773 — Charles Messier Discovers the Whirlpool Galaxy

Observation time not established

On October 13, 1773, French astronomer Charles Messier was searching the sky when he noticed a faint patch of light in the constellation Canes Venatici. It did not look like a star. Through his telescope, it appeared only as a dim, hazy object. Messier described it as a very faint nebula without stars. It would eventually become the 51st object in his famous catalog. Today we call it Messier 51—the Whirlpool Galaxy. And it is one of the most recognizable galaxies in the night sky. Messier could not possibly have understood what he had found. He was not primarily searching for distant galaxies. He was hunting comets. Comets could appear as faint fuzzy patches in eighteenth-century telescopes. Unfortunately for comet hunters, the sky contained many other objects that looked similarly hazy but remained fixed among the stars. Messier began recording these troublesome objects so that he would not repeatedly mistake them for comets. The resulting Messier Catalogue became one of astronomy's most enduring observing lists. Its objects include star clusters, nebulae, supernova remnants, and galaxies. But those categories were not yet understood as we understand them today. When Messier discovered M51, even the existence of galaxies beyond the Milky Way was unknown. To him, it was a nebula. Eight years later, in 1781, Messier's colleague Pierre Méchain identified a second nebulous object close beside M51. We now know it as NGC 5195, a smaller galaxy interacting gravitationally with the much larger Whirlpool Galaxy. But another major discovery remained. In 1845, William Parsons, the Third Earl of Rosse, turned his enormous 72-inch reflecting telescope—the “Leviathan of Parsonstown”—toward M51. Rosse saw something Messier's smaller telescope could not reveal. The nebula had a spiral structure. His drawing showed curling arms extending around a central region. M51 became the first object recognized as what astronomers then called a spiral nebula. That discovery created another mystery. What were spiral nebulae? Some astronomers thought they might be planetary systems forming within the Milky Way. Others suspected they might be enormous systems of stars at immense distances. The argument became one of the great astronomical questions of the nineteenth and early twentieth centuries. Only in the 1920s did observations of Cepheid variable stars in the Andromeda “nebula” demonstrate convincingly that objects such as Andromeda lay far beyond the Milky Way. The universe suddenly became vastly larger. Spiral nebulae were not clouds inside our galaxy. Many were galaxies themselves. Messier's faint smudge was therefore an enormous island of stars. M51 lies roughly 31 million light-years from Earth. Its graceful spiral arms contain vast lanes of gas and dust, clusters of young stars, and regions of active star formation. Its smaller companion, NGC 5195, is not merely nearby by coincidence. The two galaxies are interacting gravitationally. That interaction helps explain why the Whirlpool's spiral structure is so striking. As NGC 5195 passes near M51, its gravitational influence disturbs the larger galaxy. Gas within the spiral arms becomes compressed. Compressed clouds can collapse. New stars are born. The beautiful spiral structure is therefore not simply decorative. It records physical processes occurring on a galactic scale. Modern observatories examine M51 across the electromagnetic spectrum. Visible-light images reveal stars and dark dust lanes. Infrared observations penetrate dusty regions and trace material associated with star formation. Ultraviolet observations highlight populations of hot young stars. X-ray telescopes reveal energetic phenomena, including compact objects such as neutron stars and black holes in binary systems. At the center of M51 lies a supermassive black hole. The object that appeared to Messier as a faint blur has become an astrophysical laboratory. And its story illustrates something remarkable about scientific discovery. Messier found M51 for one reason. Astronomers value it today for entirely different reasons. He wanted to know: Is this a comet? The answer was no. But the object he cataloged to prevent future confusion became far more interesting than the comet he was seeking.

Why It Matters: Charles Messier's discovery of M51 added what would later become one of astronomy's most important galaxies to the observational record. M51 subsequently became the first nebula recognized as having spiral structure and, after astronomers learned that spiral nebulae are galaxies beyond the Milky Way, became a classic laboratory for studying galactic structure, gravitational interaction, and star formation. Its history demonstrates how an observation made for one purpose can acquire entirely new significance as scientific understanding advances.

 

Also on This Day

1994 — Magellan Ends Its Exploration of Venus

Contact lost after 10:05 UTC

On October 13, 1994, a spacecraft that had transformed humanity's knowledge of Venus entered the planet's atmosphere for the last time. Its destruction was deliberate. NASA's Magellan spacecraft had accomplished its principal mission. Now engineers intended to learn something more from its final moments. Venus presents an unusual challenge to anyone attempting to map it. Its surface is permanently concealed beneath thick clouds. Ordinary cameras in orbit cannot simply photograph the landscape below. Magellan therefore explored Venus primarily with radar. Radio waves could penetrate the clouds, reflect from the surface, and return information from which scientists could reconstruct the terrain. Magellan had launched aboard Space Shuttle Atlantis in May 1989 and entered orbit around Venus on August 10, 1990. The spacecraft then began systematically mapping the planet. What emerged was a world of extraordinary geological complexity. Magellan ultimately mapped about 98 percent of Venus's surface with radar. The images revealed enormous volcanic plains. There were great shield volcanoes. There were long lava channels. There were unusual circular volcanic features. There were broad highlands and mountain belts. There were distinctive volcanic structures sometimes called pancake domes because of their wide, flattened appearance. Impact craters were present, but their distribution indicated that the visible surface was geologically much younger than the solar system itself. The images transformed Venus from a world hidden beneath clouds into a world whose landscapes could be studied almost globally. Magellan also measured the planet's gravity field. Gravity measurements provide another way of examining a planet. Small variations in gravitational pull can reveal differences in the distribution of mass below the surface. By comparing topography with gravity, scientists can investigate the structure of the crust and mantle and ask how mountains, volcanic regions, and other large features are supported. To improve those measurements, engineers attempted something bold. They used the atmosphere of Venus itself to change Magellan's orbit. The technique is called aerobraking. Instead of using large quantities of rocket propellant to reshape an orbit, a spacecraft can repeatedly dip into the upper atmosphere. Atmospheric drag slows the spacecraft slightly on each pass. Over time, its orbit changes. In 1993, Magellan became the first planetary spacecraft to demonstrate aerobraking extensively as a means of changing its orbit. The technique subsequently became important for missions to Mars and elsewhere because it can reduce the amount of propellant a spacecraft must carry. By 1994, Magellan had vastly exceeded its original objectives. Mission controllers decided to use its final days for one more experiment. The spacecraft was commanded deeper into Venus's upper atmosphere. Its solar panels were deliberately oriented in opposite directions, somewhat like the blades of a windmill. By monitoring how the spacecraft responded to aerodynamic forces, engineers could learn about the atmosphere and about spacecraft behavior during atmospheric flight. Eventually, Magellan descended too deeply to survive. NASA's later mission chronology records that contact was lost after 10:05 UTC on October 13. The spacecraft continued descending and was destroyed in Venus's atmosphere roughly ten hours later. There would be no landing. Magellan had never been designed to survive the crushing pressures and furnace-like temperatures of the Venusian surface. Its final destination was the atmosphere of the world it had spent four years revealing. By the time it disappeared, Magellan had completed more than 15,000 orbits of Venus. NASA later calculated that the spacecraft had returned about 1,200 gigabits of data—more data than all previous NASA planetary missions combined up to that time. Its maps became fundamental reference works for the study of Venus. And decades later, scientists continue returning to Magellan's observations with new techniques and new questions. The spacecraft is gone. Its scientific life is not.

Why It Matters: Magellan transformed Venus from a planet largely concealed by clouds into a mapped geological world. Its radar observations covered about 98 percent of the surface, its gravity measurements provided clues to the planet's interior, and its pioneering use of aerobraking demonstrated a technique later employed by other planetary missions. Even its deliberately destructive finale was turned into an experiment.

 

The Bigger Picture

October 13 brings together two objects that human eyes could not readily understand. One was hidden by distance. The other was hidden by clouds. When Charles Messier looked toward M51 in 1773, his telescope showed only a faint patch. The galaxy was there in all its enormous complexity—spiral arms, star-forming regions, dust clouds, stellar populations, and a central black hole. Messier simply lacked the technology and scientific framework necessary to see what the object truly was. Venus presented a different problem. By the twentieth century, astronomers knew exactly where the planet was. It was nearby in astronomical terms. But its surface remained concealed beneath an opaque atmosphere. Again, technology changed what could be known. For M51, increasingly powerful telescopes gradually revealed structure. Lord Rosse saw its spiral form. Photography recorded details the eye could miss. Spectroscopy revealed motion and composition. Twentieth-century astronomy established that it was a separate galaxy. Space telescopes eventually examined it at wavelengths inaccessible from Earth's surface. For Venus, the breakthrough was radar. Magellan effectively looked through the clouds. The connection between the two events is therefore deeper than their difference in scale. Science is often limited not by the absence of information but by our inability to retrieve it. Sometimes the information has traveled millions of light-years and arrives as faint electromagnetic radiation. Sometimes the information lies beneath a nearby planet's clouds. The task is to devise an instrument capable of extracting it. There is another connection. Neither Messier nor Magellan reached the end of the story. Messier did not know M51 was a galaxy. Magellan did not answer every question about Venus. Science does not usually produce a final map and declare a world understood. Each improvement in observation reveals new questions. What drives M51's star formation? How exactly has its encounter with NGC 5195 altered both galaxies? Why did Venus develop so differently from Earth? How active is Venus today? Did it once possess oceans? Could its geological history help us understand why apparently similar terrestrial planets evolve in radically different directions? Those questions require new observations. October 13 therefore reminds us that exploration does not always mean physically standing somewhere. Sometimes exploration means finding a way to see what nature has hidden.

At a Glance

1773 — Observation time not established — Charles Messier discovers the object later cataloged as M51, the Whirlpool Galaxy, while observing the sky for comets.

1994 — After 10:05 UTC — NASA loses contact with Magellan during the spacecraft's deliberately commanded final descent into the atmosphere of Venus, concluding a mission that radar-mapped about 98 percent of the planet's cloud-hidden surface.

October 12

Three People Share a Spacecraft

1964 — Voskhod 1 Carries the First Multi-Person Crew into Orbit

07:30:01 UTC

On October 12, 1964, a Soviet rocket lifted from Baikonur carrying something no previous spacecraft had attempted. There were three people aboard. At 07:30:01 UTC, Voskhod 1 began the first human spaceflight with more than one person inside the same spacecraft. The crew consisted of commander Vladimir Komarov, spacecraft engineer Konstantin Feoktistov, and physician Boris Yegorov. Their flight lasted only a little more than 24 hours. Yet it represented an important transition. Until that morning, every human who had traveled into space had done so alone. Yuri Gagarin had orbited Earth alone. Alan Shepard and Gus Grissom had made their suborbital flights alone. John Glenn had orbited alone. Valentina Tereshkova had flown alone. Even when two Soviet Vostok spacecraft occupied orbit simultaneously, each contained only one cosmonaut. Future exploration could not continue that way. Journeys to the Moon, space stations, scientific laboratories, and eventually permanent orbital outposts would require people to live and work together in space. Voskhod 1 was the first step. But the spacecraft itself involved substantial compromise. Voskhod was derived from the one-person Vostok spacecraft. Rather than designing an entirely new vehicle, Soviet engineers modified the existing capsule to carry more people. Three seats were installed where one had previously been. The arrangement was extraordinarily cramped. There was so little room that the crew could not wear pressure suits. That meant Voskhod 1 lacked one of the most fundamental protections available to a space crew. If the cabin lost pressure, the cosmonauts had no individual pressure suits to keep them alive. The mission therefore achieved a spectacular first by accepting a level of risk that would later be considered unacceptable for routine human spaceflight. The changes also affected landing. Vostok cosmonauts had not landed inside their capsules. Near the end of descent, the cosmonaut ejected and parachuted separately to Earth. That system was impossible for three people packed into Voskhod. Engineers therefore added a soft-landing rocket system that fired just before touchdown, allowing the crew to remain inside the spacecraft all the way to the ground. For the first time in the Soviet human-spaceflight program, a crew would land inside its spacecraft. The people selected for Voskhod 1 were as important as the spacecraft. Komarov was the professional cosmonaut and pilot. Feoktistov was something different. He was an engineer and spacecraft designer who had worked on Soviet spacecraft development. He had also lived through extraordinary circumstances long before entering the cosmonaut corps. As a teenager during World War II, Feoktistov had served as a scout during the fighting around Voronezh. He was captured by German forces and shot but survived his wound and escaped. He later became an engineer and worked in Sergei Korolev's design organization. Now he was flying aboard technology he had helped develop. Feoktistov became the first professional spacecraft designer—and one of the first civilians—to travel into space. Yegorov represented another new kind of space traveler. He was a physician. His presence reflected growing interest in understanding what spaceflight did to the human body. During the mission, Yegorov conducted medical observations and experiments on his crewmates and himself. The crew also carried out engineering and scientific work and participated in television transmissions. Voskhod 1 completed 16 Earth orbits. Then, on October 13, the spacecraft returned. Its descent system worked. The retrorockets fired shortly before touchdown, and all three men landed safely inside their capsule in Kazakhstan. The mission had lasted approximately one day and 17 minutes. In one sense, Voskhod 1 was an evolutionary dead end. Only one more crewed Voskhod mission would fly. Voskhod 2, in March 1965, carried Pavel Belyayev and Alexei Leonov and produced another historic first when Leonov became the first person to walk in space. The Soviet program then shifted toward Soyuz, a spacecraft designed from the beginning for multi-person crews and more complex operations. But Voskhod 1 had crossed an important threshold. A spacecraft was no longer necessarily a vehicle for one person. It could be a workplace shared by people with different skills. That idea would eventually become fundamental to human spaceflight. Apollo carried three astronauts toward the Moon. Skylab and Salyut carried crews who lived and worked together. Mir hosted international crews. The International Space Station eventually became a continuously inhabited multinational laboratory. And those crews increasingly included not simply pilots but engineers, physicians, scientists, teachers, researchers, and specialists of many kinds. On October 12, 1964, three people squeezed into a capsule originally derived from a spacecraft designed for one. The arrangement was far from ideal. But human spaceflight had become a team activity.

Why It Matters: Voskhod 1 was the first spaceflight to carry more than one person in the same spacecraft and the first to place a physician and a professional spacecraft engineer in orbit. Although its cramped design required serious safety compromises, the mission marked the transition from solitary spaceflight toward the multi-person crews that would become essential for lunar missions, space stations, and long-duration exploration.

 

Also on This Day

1912 — Astronomer Lewis Boss Dies

Time unknown

On October 12, 1912, American astronomer Lewis Boss died after a career devoted to one of astronomy's most fundamental tasks: determining exactly where the stars are—and how they move. Today, a star catalog may seem less dramatic than discovering a planet or photographing a distant galaxy. But accurate stellar positions are part of the foundation upon which much of astronomy is built. Boss was born in Providence, Rhode Island, in 1846 and graduated from Dartmouth College. His career eventually led him to the Dudley Observatory in Albany, New York, where he became director. His great scientific project concerned stellar positions and proper motions. The stars appear almost fixed from one night to another. But they are not. Every star is moving through the galaxy. Because stars are so distant, their motion across the sky can be extraordinarily small. Detecting that movement requires precise measurements made over long periods. This apparent angular movement across the celestial sphere is called proper motion. Boss sought to improve astronomers' knowledge of both stellar positions and motions by combining new observations with earlier measurements. The work required extraordinary patience. A measurement made on one night becomes much more valuable when it can be compared with another made years or decades later. Boss organized observations of northern stars from the United States and southern stars from Argentina, helping create a catalog that covered the sky much more broadly. In 1910, he published the Preliminary General Catalogue of 6,188 Stars for the Epoch 1900. The catalog provided carefully determined positions and motions that astronomers could use as a reference framework. Boss did not live to complete the larger project he envisioned. After his death, the work continued under his son, astronomer Benjamin Boss. In 1937, the resulting General Catalogue of 33,342 Stars was published. The catalogs belonged to a long tradition stretching from ancient naked-eye star lists through increasingly precise telescopic surveys. That tradition continues today on a scale Boss could hardly have imagined. The European Space Agency's Gaia spacecraft has measured the positions, distances, brightnesses, and motions of enormous numbers of stars with extraordinary precision. Gaia can track stellar movements so tiny that they would have been inaccessible to early twentieth-century observers. Yet the underlying scientific idea remains familiar. Measure where stars are. Measure them again. Determine how they move. From those motions, astronomers can reconstruct the structure and history of the Milky Way. Boss also participated in another classic form of positional astronomy. In 1882, he led an expedition to Chile to observe a transit of Venus. At the time, transits of Venus were still important for refining measurements of the scale of the solar system. Boss's career therefore bridged two important astronomical endeavors: measuring the architecture of our planetary system and building increasingly accurate maps of the stars beyond it.

Why It Matters: Lewis Boss helped create increasingly precise catalogs of stellar positions and proper motions, providing fundamental reference data for astronomy. His work belongs to the centuries-long effort to transform the sky from a collection of apparent points into a measurable three-dimensional and dynamic system—a project continued today by space observatories such as Gaia.

 

The Bigger Picture

October 12 brings together two kinds of astronomical teamwork. Lewis Boss could not create a precise map of the stars from a single observation. He needed measurements accumulated over years. He needed observations from different parts of Earth. And the project he began ultimately continued after his death through the work of others. Voskhod 1 demonstrated teamwork in a more literal form. For the first time, several people occupied the same spacecraft. That change may seem obvious from our modern perspective. We are accustomed to seeing crews aboard the International Space Station. But the earliest spacecraft were so small and so limited that human spaceflight was fundamentally a solitary experience. Voskhod 1 began changing that. Its crew also represented a deeper transformation. The first space travelers had been selected principally for their abilities as pilots. That made sense. Early spacecraft were experimental vehicles operating in an extraordinarily dangerous environment. But if space was eventually going to become a place where people conducted science, built structures, repaired equipment, practiced medicine, and explored other worlds, pilots alone would not be enough. Voskhod 1 carried an engineer. It carried a physician. Space was becoming a place for specialists. That development would continue. Geologists would walk on the Moon. Scientists would work aboard Skylab. Physicians would study human adaptation to long-duration spaceflight. Astronomers would operate telescopes above the atmosphere. Engineers would assemble and repair spacecraft in orbit. International crews would live together for months at a time. And the distinction between “astronaut” and “scientist,” or between “cosmonaut” and “engineer,” would become increasingly blurred. There is also an important caution in the Voskhod story. Progress should not be measured simply by the number of records broken. The Soviet Union wanted another dramatic space first. Putting three people into orbit before the United States launched its two-person Gemini spacecraft accomplished that objective. But fitting three people into a modified one-person spacecraft required eliminating their pressure suits and accepting significant risk. The mission succeeded. That does not mean the risk was wise. Space history repeatedly teaches that achievement and safety are not automatically the same thing. The best exploration is not merely exploration that reaches farther or gets there first. It is exploration that learns, improves, and builds capabilities that can endure. Lewis Boss built catalogs that others could improve. Voskhod demonstrated multi-person flight, but Soyuz would turn multi-person spaceflight into a sustainable system. Both stories remind us that enduring progress is built not simply from individual achievements but from knowledge and capability that other people can carry forward.

At a Glance

1912 — Time unknown — American astronomer Lewis Boss dies after a career devoted to increasingly precise catalogs of stellar positions and proper motions.

1964 — 07:30:01 UTC — Voskhod 1 launches Vladimir Komarov, Konstantin Feoktistov, and Boris Yegorov into orbit, beginning the first spaceflight to carry more than one person aboard the same spacecraft.

October 11

Apollo Returns to Flight

1968 — Apollo 7 Carries the Apollo Program Back into Space

15:02:45 UTC

On October 11, 1968, three astronauts sat atop a Saturn IB rocket at Cape Kennedy's Launch Complex 34. Below them was the same launch complex where, less than two years earlier, tragedy had struck the Apollo program. On January 27, 1967, astronauts Virgil “Gus” Grissom, Edward White, and Roger Chaffee had died when fire swept through the Apollo 1 command module during a ground test. The accident exposed serious problems in spacecraft design, materials, testing procedures, manufacturing, and management. NASA halted crewed Apollo flights. The spacecraft was extensively redesigned. Now it had to prove itself. At 15:02:45 UTC on October 11, 1968, Apollo 7 lifted from Launch Complex 34. Commander Walter “Wally” Schirra, command module pilot Donn Eisele, and lunar module pilot Walter Cunningham became the first people to fly aboard an Apollo spacecraft. There was no lunar module on this mission. There would be no journey to the Moon. Apollo 7 would remain in Earth orbit. But the success of the entire lunar program depended upon what happened there. The spacecraft was the redesigned Block II Command and Service Module, incorporating many of the changes made after Apollo 1. The dangerous inward-opening hatch had been replaced with a hatch that could be opened much more quickly. Flammable materials inside the cabin had been reduced or replaced. Wiring and plumbing were improved. Quality-control procedures were strengthened. The spacecraft had undergone thousands of changes. Now astronauts would test it in the environment for which it had been designed. Apollo 7 entered Earth orbit normally. Over the next 10 days, 20 hours, 9 minutes, and 3 seconds, the crew would put the spacecraft through an exhaustive series of tests. They fired the large Service Propulsion System engine repeatedly. This engine was especially important. On future lunar missions it would be responsible for major maneuvers, including entering and leaving lunar orbit. If it failed at the wrong moment, astronauts could be stranded far from Earth. Apollo 7 demonstrated that the engine could restart reliably. The crew also practiced maneuvers associated with rendezvous. After separating from the Saturn IVB upper stage, Schirra turned the Apollo spacecraft around and approached the spent stage as though it were a lunar module. Future Apollo crews would have to perform related maneuvers during missions to the Moon. The spacecraft's electrical, communications, guidance, navigation, environmental-control, and propulsion systems were tested repeatedly. The mission also introduced millions of people to another feature of Apollo. Live television from space. NASA had initially been reluctant to devote valuable crew time to television broadcasts. Schirra himself resisted an early request when it conflicted with the flight plan. But once transmissions began, viewers saw the astronauts floating inside the spacecraft and looking down at Earth. The broadcasts became enormously popular. Apollo 7's crew eventually received a special Emmy Award for the television coverage. The mission was not without difficulties. All three astronauts developed head colds. In weightlessness, congestion can be especially uncomfortable because bodily fluids do not drain in the familiar way they do on Earth. Fatigue, crowded working conditions, an ambitious flight plan, and disagreements with Mission Control contributed to increasing tension between the crew and controllers. The relationship became famously contentious. But those interpersonal difficulties should not obscure the technical result. The spacecraft worked. Apollo 7 completed 163 Earth orbits and traveled more than 4.5 million miles. On October 22, the command module splashed down safely in the Atlantic Ocean. NASA considered the spacecraft's performance sufficiently successful to make an extraordinary decision. The next crewed Apollo mission would not simply repeat Apollo 7 at a greater distance. Apollo 8 would go to the Moon. Only about two months after Apollo 7 returned, Frank Borman, Jim Lovell, and Bill Anders would become the first humans to leave Earth orbit, travel to another world, and orbit the Moon. Apollo 7 had made that decision possible. And less than a year after Schirra, Eisele, and Cunningham lifted from Launch Complex 34, Apollo 11 would land on the lunar surface.

Why It Matters: Apollo 7 was the first crewed flight of the redesigned Apollo spacecraft after the Apollo 1 tragedy. Its successful 11-day test demonstrated that the Command and Service Module could support the demanding missions ahead and gave NASA the confidence to send Apollo 8 around the Moon. Apollo 7 was therefore one of the crucial bridge missions between tragedy on the launch pad and the first human footsteps on another world.

 

Also on This Day

1958 — Pioneer 1 Becomes the First Spacecraft Launched by NASA

08:42:13 UTC

Only ten days after NASA officially began operations, the new agency attempted to send a spacecraft toward the Moon. At 08:42:13 UTC on October 11, 1958, a Thor-Able rocket lifted from Cape Canaveral carrying a small spacecraft originally known as Able 2. It soon became Pioneer 1. The mission had been inherited from programs already underway before NASA's creation, and the launch vehicle remained under U.S. Air Force responsibility. But Pioneer 1 became the first spacecraft launched under NASA's newly established authority. Its objective was ambitious. The spacecraft was intended to travel to the Moon and enter lunar orbit. Pioneer 1 weighed only about 38 kilograms—84 pounds. Its instruments included an ion chamber for measuring radiation, a magnetometer, a micrometeoroid detector, temperature sensors, and a television system intended to obtain images of the Moon. The mission did not proceed as planned. The launch vehicle's upper stage did not provide the required velocity. Pioneer 1 was traveling too slowly to reach the Moon. But the mission did not immediately end. The spacecraft climbed far beyond Earth before gravity pulled it back. It reached an altitude of approximately 114,000 kilometers, or about 71,000 miles—farther from Earth than any previous human-made object had traveled. During its flight, Pioneer 1 transmitted scientific information about the environment beyond Earth. Its measurements contributed to the rapidly developing study of Earth's radiation environment, which had received a major surprise earlier that year when Explorer 1 and Explorer 3 helped reveal the Van Allen radiation belts. After approximately 43 hours of flight, Pioneer 1 reentered Earth's atmosphere over the South Pacific on October 13. It had failed to reach its intended destination. Yet it had still traveled farther than any spacecraft before it and returned useful scientific information. Its historical importance also lies in its timing. NASA had begun operations only on October 1, 1958. Ten days later, it was already attempting to reach another world. The agency's first spacecraft mission was therefore not a cautious Earth-orbiting experiment. It was an attempted lunar mission.

Why It Matters: Pioneer 1 was the first spacecraft launched under NASA's authority and demonstrated the new agency's immediate ambition to move beyond Earth orbit. Although a launch-vehicle malfunction prevented it from reaching the Moon, the spacecraft set a distance record and returned useful measurements from near-Earth space.

1984 — Kathryn Sullivan Becomes the First American Woman to Walk in Space

EVA duration: 3 hours, 29 minutes

Six days after Space Shuttle Challenger launched on STS-41G, astronauts Kathryn Sullivan and David Leestma opened the airlock and moved into the Shuttle's payload bay. For Sullivan, October 11, 1984, became a historic day. She was the first American woman to perform a spacewalk. Sullivan was a geologist and oceanographer who had joined NASA as part of the astronaut class selected in 1978. That class fundamentally changed the composition of the American astronaut corps. It included NASA's first women astronauts and the first Black and Asian American astronauts selected for the corps. Sullivan and Sally Ride were both aboard STS-41G, making the mission the first spaceflight to include two women. But Sullivan was not the first woman anywhere in the world to perform a spacewalk. That distinction belonged to Soviet cosmonaut Svetlana Savitskaya, who had conducted an EVA outside the Salyut 7 space station on July 25, 1984. Sullivan's milestone came less than three months later. Her spacewalk was not performed primarily to set a record. She and Leestma had work to do. One of their major tasks involved the Orbital Refueling System. Engineers wanted to determine whether spacecraft could someday be refueled while already in orbit. Such a capability could extend the operating lives of satellites and make spacecraft servicing more practical. The astronauts therefore demonstrated techniques for handling equipment and transferring fluids in weightlessness. The work involved hydrazine, a highly toxic propellant used by many spacecraft, although the demonstration used procedures designed to test the system safely. The EVA lasted 3 hours and 29 minutes. Sullivan also inspected equipment in Challenger's payload bay, including the large antenna associated with the Shuttle Imaging Radar experiment. The spacewalk added another milestone to a mission already filled with them. STS-41G carried the first seven-person spacecraft crew. It was the first mission with two women aboard. Sally Ride became the first American woman to make a second spaceflight. Marc Garneau became the first Canadian in space. And now Sullivan had become the first American woman to work outside a spacecraft. Her career would continue. She later flew aboard Discovery on STS-31, the mission that deployed the Hubble Space Telescope in 1990. Decades after leaving NASA, Sullivan accomplished another extraordinary first. In 2020, she descended to Challenger Deep in the Mariana Trench, becoming the first woman to reach the deepest known point in Earth's oceans—and the first person to have both walked in space and visited Challenger Deep.

Why It Matters: Kathryn Sullivan's spacewalk marked another important expansion of participation in human spaceflight while also serving a practical engineering purpose. Her EVA with David Leestma tested techniques for orbital refueling, demonstrating that milestones in who explores space can occur alongside advances in what people are capable of doing there.

 

The Bigger Picture

October 11 is a day about building capability. Pioneer 1 attempted something NASA could not yet accomplish. Apollo 7 demonstrated something NASA absolutely had to accomplish. Kathryn Sullivan demonstrated something spacefarers hoped would become increasingly routine. Together, the three events show that progress in spaceflight is rarely a single leap from impossibility to mastery. It develops through stages. In 1958, NASA tried to reach the Moon only ten days after beginning operations. Pioneer 1 failed to get there. But the mission traveled farther from Earth than any previous spacecraft and returned useful data. Failure and achievement occupied the same flight. Ten years later, Apollo 7 faced a different challenge. NASA already knew how to place astronauts into Earth orbit. The question was whether the redesigned Apollo spacecraft could be trusted after the deaths of Grissom, White, and Chaffee. Apollo 7 provided the answer. It worked. That success allowed NASA to take the extraordinary next step of sending Apollo 8 to the Moon. By 1984, human spaceflight had matured further. Astronauts were not simply passengers proving that humans could survive beyond Earth. They were workers. Sullivan and Leestma went outside Challenger to experiment with technology for servicing spacecraft in orbit. This progression is important. Reach space. Learn to operate there safely. Learn to work there. And then expand what becomes possible. October 11 also reminds us that progress is not the same as perfection. Pioneer 1 missed the Moon. Apollo 7 succeeded technically while experiencing significant tension between its crew and Mission Control. Orbital refueling did not immediately become the routine practice envisioned by the STS-41G experiment. Yet each contributed knowledge. Space exploration advances not only through spectacular successes but through tests, partial successes, failures, redesigns, and lessons carried forward. Apollo 7 demonstrates that principle especially clearly. The spacecraft that rose from Launch Complex 34 in October 1968 existed in its redesigned form because another spacecraft had failed catastrophically on that same launch complex. NASA had investigated. Engineers had redesigned. Procedures had changed. Then people flew again. Less than ten months after Apollo 7 launched, humans stood on the Moon. The path from Earth to another world was not a straight line. It was a process of learning what worked, confronting what did not, and trying again.

At a Glance

1958 — 08:42:13 UTC — Pioneer 1 launches toward the Moon, becoming the first spacecraft launched under the authority of the newly operational NASA; a launch-vehicle malfunction prevents it from reaching its intended lunar destination.

1968 — 15:02:45 UTC — Apollo 7 launches Wally Schirra, Donn Eisele, and Walt Cunningham on the first crewed Apollo mission, beginning the critical Earth-orbital test of the redesigned Command and Service Module.

1984 — EVA duration 3 hours, 29 minutes — Kathryn Sullivan leaves Space Shuttle Challenger with David Leestma during STS-41G, becoming the first American woman to walk in space while helping demonstrate orbital-refueling techniques.

October 10

The Rules for a New Frontier

1967 — The Outer Space Treaty Enters into Force

Time not applicable

On October 10, 1967, an international treaty entered into force addressing a place where humanity had arrived only ten years earlier. Outer space. When Sputnik 1 launched on October 4, 1957, there was no comprehensive international legal framework specifically governing what nations could claim, place, build, or do beyond Earth. Now satellites circled the planet. Humans had traveled into orbit. Spacecraft had reached the Moon and Venus. The United States and Soviet Union were racing to land people on the Moon. And the same rockets capable of launching spacecraft were closely related to ballistic missiles capable of carrying nuclear weapons. The question was no longer whether humanity would operate in space. It was: What rules would apply when we did? The answer began to take shape through the United Nations. On January 27, 1967, the United States, Soviet Union, United Kingdom, and other nations began signing the Treaty on Principles Governing the Activities of States in the Exploration and Use of Outer Space, including the Moon and Other Celestial Bodies. It became known much more simply as the Outer Space Treaty. On October 10, after the required ratifications had been deposited, the treaty entered into force. Its principles were remarkable. First, outer space was declared free for exploration and use by all nations. No country could claim the Moon, a planet, an asteroid, or another celestial body as sovereign national territory. Planting a flag would not create a new province. Landing first would not establish ownership. Occupation would not confer sovereignty. The treaty stated that outer space, including the Moon and other celestial bodies, was not subject to national appropriation. That principle became one of the foundations of space law. The treaty also addressed the military use of space. Nations agreed not to place nuclear weapons or other weapons of mass destruction in Earth orbit, station them in outer space, or install them on celestial bodies. The Moon and other celestial bodies were to be used exclusively for peaceful purposes. Military bases, weapons testing, and military maneuvers on celestial bodies were prohibited. The treaty did not completely demilitarize space. Military satellites, reconnaissance systems, communications spacecraft, and other national-security activities could still operate in Earth orbit. But the agreement established significant limits at a moment when the Cold War could easily have extended the nuclear arms race into another domain. The treaty also established responsibility. A nation could not avoid its international obligations simply because a space activity was conducted by a private company rather than directly by its government. States were made internationally responsible for their national activities in outer space, including those conducted by non-governmental entities. Private space activities therefore required governmental authorization and continuing supervision. That provision has become increasingly significant as commercial companies have assumed larger roles in launching satellites, carrying astronauts, exploring the Moon, and planning future activities beyond Earth. Another principle concerned astronauts. The treaty described them as “envoys of mankind” and called upon nations to assist astronauts in distress. Still another concerned damage. Launching states could be held internationally liable for damage caused by their space objects. And one provision has become especially important to planetary exploration. Article IX called upon nations to conduct exploration so as to avoid harmful contamination of the Moon and other celestial bodies, as well as harmful effects on Earth resulting from the introduction of extraterrestrial matter. This is one of the legal foundations underlying what is now called planetary protection. When spacecraft are sterilized or cleaned before traveling to potentially habitable environments, the concern is partly scientific. Scientists do not want terrestrial microorganisms contaminating a world such as Mars or an icy moon and confusing future searches for extraterrestrial life. When missions are deliberately ended to prevent an uncontrolled spacecraft from eventually striking a potentially habitable world, the same principle is involved. We have already encountered striking examples in this chronology. Galileo was deliberately sent into Jupiter in 2003 partly to eliminate any possibility that the spacecraft might eventually contaminate Europa. Cassini was deliberately plunged into Saturn in 2017 to protect Enceladus and Titan. Those decisions belong to a tradition of responsible exploration whose international legal framework reaches back to the Outer Space Treaty. The treaty was negotiated during the Cold War. Yet the United States and Soviet Union—competitors in an intense technological and ideological struggle—agreed that some principles should apply to everyone. That may be one of its most remarkable features. The treaty did not answer every future question. It did not anticipate reusable commercial launch systems, enormous satellite constellations, private lunar landers, asteroid-resource proposals, or permanent settlements on other worlds. Debates continue over how its principles should apply to those developments. But more than half a century after it entered into force, the Outer Space Treaty remains the foundation upon which much of international space law is built.

Why It Matters: The Outer Space Treaty established the fundamental international principles governing human activity beyond Earth. It rejected national sovereignty over celestial bodies, guaranteed freedom of exploration, prohibited nuclear weapons and other weapons of mass destruction from being stationed in space, established national responsibility for governmental and private activities, and required attention to harmful contamination. It transformed outer space from a technologically accessible frontier into a realm governed, however imperfectly, by international law.

 

Also on This Day

1846 — William Lassell Discovers Triton

Observation time not established

On October 10, 1846, English astronomer William Lassell pointed his telescope toward a newly discovered planet. Only 17 days earlier, Johann Gottfried Galle and Heinrich Louis d'Arrest had identified Neptune from the Berlin Observatory, guided by mathematical predictions of its position. Now Lassell saw something near it. A moon. The object would eventually be named Triton. The speed of the discovery was extraordinary. Astronomers had spent years trying to understand irregularities in the orbit of Uranus. Mathematicians Urbain Le Verrier in France and John Couch Adams in Britain independently calculated that the gravitational pull of an unknown planet could explain those discrepancies. On September 23, 1846, Galle and d'Arrest found Neptune close to the position predicted by Le Verrier. News of the discovery spread quickly. Lassell, a successful brewer and accomplished amateur astronomer living near Liverpool, immediately turned his attention toward the new world. He possessed an important advantage. He built his own telescopes. Lassell had constructed a powerful 24-inch reflecting telescope, using a metal mirror he had ground and polished himself. With it, on October 10, he detected a faint companion to Neptune. Triton proved to be no ordinary moon. It is by far Neptune's largest satellite, with a diameter of approximately 2,700 kilometers. More surprisingly, Triton travels around Neptune in the opposite direction from the planet's rotation. This retrograde orbit is a powerful clue to its history. Large moons generally form from disks of material surrounding their planets and therefore orbit in the same general direction that their planets rotate. Triton probably did not form that way. Scientists now think it began as an independent world in the outer solar system—probably a Kuiper Belt object—and was later captured by Neptune's gravity. That capture would have profoundly disturbed Neptune's original satellite system. Triton's orbit eventually became nearly circular, but the process may have destroyed or ejected earlier moons and contributed to the formation of the irregular satellite system seen today. For more than a century after Lassell's discovery, Triton remained little more than a distant point of light. Then, in 1989, Voyager 2 flew past Neptune. Its cameras transformed Triton from a dot into a world. The surface was extraordinarily cold—about −235 degrees Celsius. Much of it was covered with frozen nitrogen and other ices. The terrain included broad plains, fractures, and unusual regions sometimes described as having a “cantaloupe” texture. Most surprising of all, Voyager saw active geyser-like plumes rising several kilometers above the surface. Even at the edge of the planetary system, on one of the coldest surfaces ever visited by a spacecraft, geological activity was occurring. Triton's strange orbit and Pluto-like characteristics have made it especially important to planetary scientists. Studying Triton may provide a way to examine a captured Kuiper Belt world without traveling all the way into the Kuiper Belt itself. Lassell could have known none of this. He saw only a faint point beside a newly discovered planet. But that point turned out to be one of the strangest large moons in the solar system.

Why It Matters: Triton's discovery, only 17 days after Neptune itself was found, quickly established that the newly discovered planet possessed a satellite system. Triton's retrograde orbit later revealed that it probably formed elsewhere and was captured by Neptune, while Voyager 2 showed it to be an unexpectedly active icy world and a likely relative of objects in the Kuiper Belt.

 

The Bigger Picture

October 10 brings together two very different kinds of discovery. In 1846, humanity was discovering what was out there. In 1967, humanity was beginning to decide how we should behave when we got there. The interval between those events tells an extraordinary story. Lassell could study Triton only as a distant point of light. One hundred and eleven years later, Sputnik crossed the boundary between observing space and entering it. Another decade passed. By October 1967, humans had orbited Earth, robotic spacecraft had landed on the Moon and Venus, and preparations were underway for people to travel to the Moon. The universe had not changed. Our relationship with it had. Once exploration became physically possible, astronomy encountered questions that astronomy alone could not answer. Who owns the Moon? Can a nation claim Mars? What responsibilities does a country have for a privately operated spacecraft? What happens if one nation's spacecraft damages another nation's property? Should terrestrial organisms be allowed to contaminate another world? What kinds of weapons should be permitted beyond Earth? These are questions of law, ethics, diplomacy, science, and politics as much as engineering. And they will become more important as exploration expands. Triton itself provides an interesting thought experiment. No spacecraft has landed there. No human has visited Neptune. But if someday explorers reach Triton, the principles established in 1967 would accompany them. No nation could legally declare Triton its sovereign territory under the treaty. Exploration would carry responsibilities as well as opportunities. And because Triton is an active world containing volatile ices and potentially scientifically sensitive environments, questions of contamination would matter greatly. This is the larger lesson of October 10. Discovery creates knowledge. Exploration creates capability. But capability creates responsibility. Humanity's journey into the universe is therefore not only the story of how far we can travel. It is also the continuing question of what we choose to do when we arrive.

At a Glance

1846 — Observation time not established — William Lassell discovers Triton, Neptune's largest moon, only 17 days after the discovery of Neptune itself.

1967 — Time not applicable — The Outer Space Treaty enters into force, establishing fundamental principles governing international activities in outer space, on the Moon, and on other celestial bodies.

October 9

A New Star Changes the Heavens

1604 — A Brilliant New Star Appears in the Milky Way

Evening; precise time not established

On the evening of October 9, 1604, Italian astronomer Ilario Altobelli looked toward a striking gathering of planets in the constellation Ophiuchus. Mars, Jupiter, and Saturn were close together in the sky. Altobelli had been watching the region carefully. Now something was different. There was another brilliant point of light. A new star had appeared. Today we know that Altobelli was witnessing a supernova—the catastrophic destruction of a star roughly 20,000 light-years from Earth. It became known as Kepler's Supernova, or SN 1604. It remains the most recent supernova known to have been observed occurring in our own Milky Way galaxy. Altobelli's role deserves particular attention. The supernova carries Johannes Kepler's name, which can easily create the impression that Kepler discovered it. He did not. Historical evidence indicates that Altobelli observed the new object in northern Italy on October 9. Other observers soon reported it independently. In Prague, Johannes Brunowski noticed it on October 10 and brought it to Kepler's attention. Cloudy weather prevented Kepler from seeing it himself until October 17. Once he did, however, Kepler studied the object extensively. His careful observations and subsequent publication made his name permanently associated with the event. The new star was impossible to ignore. It eventually became brighter than Jupiter and remained visible to the unaided eye for many months. At its brightest, it could even be seen during daylight. For seventeenth-century astronomy, the event presented a profound question. Where was it? The answer mattered because European natural philosophy was still heavily influenced by the cosmology of Aristotle. In the traditional Aristotelian universe, the region below the Moon was a realm of change. Things were born. Things decayed. Things moved and transformed. But beyond the Moon lay the supposedly perfect and unchanging heavens. Stars belonged to that eternal celestial realm. A genuinely new star would therefore be deeply troublesome. One possibility was that the object was not actually among the stars at all. Perhaps it was a phenomenon in Earth's atmosphere. Astronomers could test that possibility using parallax. A nearby object viewed from different locations should appear to shift relative to the distant stars. The new object showed no measurable parallax with the instruments available. That placed it far beyond the Moon. Something in the supposedly unchanging heavens had changed. This was not the first time such evidence had appeared. In 1572, Tycho Brahe had studied another brilliant “new star”—also a supernova—and similarly found no measurable parallax. The great comet of 1577 had further undermined the traditional idea that the celestial spheres were solid, immutable structures. SN 1604 added another powerful piece of evidence. The heavens were not changeless. Kepler followed the object as its brightness evolved and published his observations in 1606 in a work commonly known by its shortened title, De Stella Nova—On the New Star. The telescope had not yet entered astronomy. Galileo's telescopic observations would begin only a few years later. Everything astronomers learned about the new star in 1604 therefore came from careful naked-eye observation, positional measurement, and reasoning. They could not know what the object physically was. The nature of supernovae would remain unknown for centuries. Today astronomers identify SN 1604 as a Type Ia supernova. Such explosions involve white dwarfs—extremely dense stellar remnants—in binary systems. A thermonuclear runaway destroys the white dwarf, releasing an enormous amount of energy. The original explosion is long over. But it left something behind. An expanding shell of gas and energetic particles known as Kepler's Supernova Remnant still occupies the region. Modern observatories examine that remnant at wavelengths Altobelli and Kepler could never have imagined. Visible-light telescopes study its glowing structures. Radio telescopes examine energetic particles and magnetic fields. Infrared observatories investigate heated dust. X-ray telescopes reveal gas heated to millions of degrees by the expanding shock wave. Four centuries after the new star appeared, the explosion is still teaching us about the deaths of stars. There is also a humbling perspective hidden within the date. The supernova did not actually explode in 1604. Because it lies roughly 20,000 light-years away, the light that reached Earth that October had been traveling through the Milky Way for approximately 20,000 years. The explosion had occurred long before recorded human history. October 9, 1604, marks not when the star exploded, but when news of that explosion finally reached human eyes.

Why It Matters: SN 1604 is the most recent supernova known to have been observed occurring in the Milky Way. Its appearance provided further evidence that the heavens were not perfect and unchanging, helping undermine an ancient cosmological assumption just before telescopic astronomy transformed humanity's understanding of the universe. The surviving remnant remains an important astronomical laboratory more than four centuries later.

 

Also on This Day

1992 — The Peekskill Meteorite Hits a Parked Car

Fireball observed approximately 23:48 UTC

On the evening of October 9, 1992, spectators at high-school football games across the eastern United States noticed something extraordinary moving through the sky. A brilliant fireball streaked overhead. Unlike most meteors of its era, however, this one had an unusually large audience equipped with video cameras. The result was one of the best-recorded meteor events in history up to that time. The object entered Earth's atmosphere over the eastern United States and traveled northeastward in a long luminous trajectory. Thousands of people saw it. At least 16 independent videos recorded portions of its passage. Those recordings became scientifically valuable. Because the meteor had been photographed from multiple locations, researchers could reconstruct its atmospheric trajectory and estimate the orbit it had followed around the Sun before encountering Earth. But the most famous part of the story happened on the ground. In Peekskill, New York, 18-year-old Michelle Knapp heard a loud crash outside her home. A rock from space had struck her parked 1980 Chevrolet Malibu. The meteorite punched through the rear of the car, leaving a large dent and a hole, before coming to rest beneath it. The recovered stone weighed approximately 12.4 kilograms—more than 27 pounds. It was identified as an H6 ordinary chondrite, part of one of the most common broad classes of stony meteorites. The car quickly became almost as famous as the meteorite. But scientifically, the videos were more important. Meteorites are pieces of asteroids that survive atmospheric passage and reach the ground. Usually, scientists can analyze the recovered stone but have limited information about precisely how that particular object traveled through the solar system before falling. Peekskill provided both. The videos documented the atmospheric trajectory. The meteorite provided the physical sample. Researchers could therefore connect a laboratory specimen with information about the orbit of its parent meteoroid before it encountered Earth. The event anticipated a connection we encountered only two days ago with 2008 TC3. In 1992, cameras recorded a meteorite-producing object primarily as it traveled through Earth's atmosphere. In 2008, astronomers detected 2008 TC3 before it entered the atmosphere and predicted its impact. Together, such events show how asteroid astronomy, meteor science, orbital mechanics, and laboratory analysis increasingly became parts of the same field.

Why It Matters: The Peekskill meteorite became one of the best-documented meteorite falls of its time because its brilliant atmospheric passage was recorded on numerous independent videos and a substantial fragment was recovered. Those observations allowed scientists to connect a meteorite studied in the laboratory with the trajectory of the object that delivered it to Earth.

2009 — LCROSS Strikes the Moon and Finds Water

Centaur impact: 11:31:19.51 UTC
LCROSS impact: 11:35:34 UTC

On October 9, 2009, NASA deliberately crashed a rocket into the Moon. Four minutes later, it crashed a spacecraft nearby. This was not a failure. It was the experiment. The Lunar Crater Observation and Sensing Satellite—LCROSS—had been launched with the Lunar Reconnaissance Orbiter on June 18, 2009. Its principal question was one of enormous importance for lunar science and future exploration: Is there water ice in the permanently shadowed craters near the Moon's poles? For most of the twentieth century, the Moon was widely imagined as almost completely dry. But spacecraft observations had gradually complicated that picture. Radar and neutron measurements provided evidence suggesting that hydrogen-rich material—and possibly water ice—might exist near the lunar poles. There was a reason to look there. Because the Moon's rotational axis is only slightly tilted, sunlight never reaches the floors of some deep craters near the poles. These permanently shadowed regions can remain extraordinarily cold. For billions of years, they may have acted as cold traps, preserving volatile substances delivered by comets and asteroids or produced through other processes. LCROSS was designed to look inside one. The target was Cabeus crater, near the lunar south pole. The mission used an ingenious approach. The spent Centaur upper stage that had helped launch LCROSS was retained as an impactor. At 11:31:19.51 UTC, the roughly two-ton Centaur slammed into the permanently shadowed floor of Cabeus. The impact excavated hundreds of tons of lunar material and threw part of it upward. Material that may have remained in darkness for billions of years suddenly rose into sunlight. LCROSS followed approximately four minutes behind. Its cameras and spectrometers watched the impact and examined the resulting plume. Then the spacecraft flew directly through the debris. It transmitted its measurements to Earth until, at 11:35:34 UTC, LCROSS itself struck the Moon. The mission was over. The analysis was just beginning. The visible plume proved less dramatic than many observers had expected. But LCROSS's instruments had obtained the measurements that mattered. On November 13, NASA announced the result: water had been detected. Subsequent analysis strengthened and expanded the conclusion. The excavated material contained water and other volatile substances. Later measurements indicated that some lunar polar deposits contained grains of relatively pure water ice. The Moon was not simply the bone-dry world once imagined. Its permanently shadowed regions preserved a chemically rich record. The discovery had implications extending beyond lunar geology. Water is useful. Future explorers could potentially use lunar ice for drinking water. Water can be separated into hydrogen and oxygen, potentially providing breathable oxygen and ingredients for rocket propellant. Whether particular deposits can practically and responsibly be used remains a question for future exploration. But the presence of accessible lunar water fundamentally changes discussions about sustained activity on the Moon.

Why It Matters: LCROSS provided direct evidence of water in a permanently shadowed crater near the Moon's south pole. The discovery transformed scientific understanding of lunar volatiles and helped establish the polar regions as some of the most important locations for future lunar science and exploration.

 

The Bigger Picture

October 9 is a day about things that were present before we understood they were there. SN 1604 suddenly appeared in the night sky. But the star had actually exploded thousands of years earlier. The light simply had not reached Earth yet. The Peekskill meteoroid traveled through the solar system before intersecting Earth's orbit. Human beings became aware of it only when the atmosphere turned its arrival into a brilliant streak of light. Water had probably existed in the permanently shadowed regions of the Moon for immense spans of time before LCROSS excavated some of it into sunlight. In every case, discovery did not create the phenomenon. Discovery changed our awareness of it. That distinction lies at the heart of astronomy. The universe does not reveal itself according to the timetable of human understanding. Stars explode whether anyone is watching. Asteroids cross planetary orbits whether anyone has discovered them. Ice accumulates in darkness whether anyone has sent a spacecraft to look. Science gives us ways to notice what was already there. There is another progression across the three events. In 1604, astronomers possessed their eyes and geometry. In 1992, video cameras captured a meteor from many different locations, allowing computers and mathematics to reconstruct its path. In 2009, scientists did something more active. They deliberately performed an experiment on another world. LCROSS did not merely observe the Moon. It struck the surface in a carefully selected location so that buried material would be exposed and measured. Astronomy had evolved from observing what the universe presented to us into designing experiments on worlds beyond Earth. And yet the basic motivation remained the same. There was something we did not know. So we found a way to look.

At a Glance

1604 — Evening; precise time not established — Ilario Altobelli makes the earliest known reported observation of the brilliant new star now called SN 1604 or Kepler's Supernova, the most recent supernova known to have been observed occurring in the Milky Way.

1992 — Approximately 23:48 UTC — The Peekskill fireball crosses the eastern United States; a 12.4-kilogram meteorite fragment subsequently strikes a parked automobile in Peekskill, New York.

2009 — 11:31:19.51 UTC — LCROSS's Centaur upper stage impacts Cabeus crater near the Moon's south pole, excavating material from a permanently shadowed region.

2009 — 11:35:34 UTC — The LCROSS shepherding spacecraft, after observing and passing through the Centaur's debris plume, impacts the Moon; its measurements subsequently confirm the presence of lunar water.

October 8

Finding Order Among the Stars

1873 — Ejnar Hertzsprung Is Born

Time unknown

On October 8, 1873, Ejnar Hertzsprung was born in Frederiksberg, Denmark, near Copenhagen. His name would eventually become attached to one of the most important diagrams in all of astronomy. The Hertzsprung-Russell diagram looks deceptively simple. Place stars according to their luminosity on one axis. Place them according to surface temperature—or a closely related measure such as color or spectral type—on the other. Then something remarkable happens. The stars do not scatter randomly across the diagram. They form patterns. Those patterns reveal the life stories of stars. Hertzsprung did not begin his career as a professional astronomer. He trained as a chemical engineer at the Polytechnic Institute in Copenhagen and subsequently worked in St. Petersburg and studied photochemistry in Leipzig. Photography helped draw him toward astronomy. By the early twentieth century, astronomers had accumulated enormous amounts of information about stars. Spectroscopy allowed them to divide stars into spectral classes according to the absorption lines in their light. Photography allowed increasingly precise measurements of stellar brightness and position. But an important question remained: What did these classifications actually tell astronomers about the physical nature of stars? Hertzsprung recognized that stars with similar spectra could nevertheless possess very different intrinsic luminosities. Some were enormously luminous. Others were comparatively faint. In papers published in 1905 and 1907, he distinguished between what came to be called giant and dwarf stars. The distinction was profound. Two stars could have approximately the same surface temperature and therefore similar colors and spectra, yet one could radiate vastly more energy than the other because it was physically much larger. Hertzsprung began examining the relationship between stellar color and absolute brightness. When he plotted stars according to these properties, patterns appeared. Independently, American astronomer Henry Norris Russell approached the same relationship from another direction and developed a similar graphical representation. The resulting relationship became known as the Hertzsprung-Russell diagram, usually abbreviated the H-R diagram. Its importance is difficult to overstate. Most ordinary stars occupy a broad diagonal band called the main sequence. Hot, luminous stars appear toward one end. Cooler, fainter stars appear toward the other. Our Sun lies on this main sequence. But not all stars do. Giants and supergiants occupy regions of much greater luminosity. White dwarfs occupy a region containing hot but faint stars—objects whose high temperatures are combined with extremely small physical sizes. At first, the diagram was principally an empirical relationship. Astronomers could see that stars occupied different regions. As stellar astrophysics developed, however, the reason became clearer. The H-R diagram is, in effect, a map of stellar evolution. A star spends most of its life on the main sequence, generating energy by fusing hydrogen into helium in its core. When the core hydrogen becomes depleted, the star changes. Its internal structure adjusts. It may expand into a red giant. Depending upon its mass, later stages can carry it toward a white dwarf, supernova explosion, neutron star, or black hole. Star clusters made the diagram even more powerful. Because stars within a cluster generally formed at approximately the same time and lie at approximately the same distance from Earth, astronomers could compare their positions on the H-R diagram and determine where stars of different masses had begun leaving the main sequence. That main-sequence turnoff became an important method for estimating the ages of star clusters. Hertzsprung also made important contributions to the study of variable stars and stellar distances. He recognized the importance of Henrietta Swan Leavitt's discovery of the period-luminosity relationship among Cepheid variable stars and helped apply that relationship to the astronomical distance scale. He also became an expert in the photographic study of double stars. In 1919, Hertzsprung joined the Leiden Observatory in the Netherlands. He became its director in 1935 and remained there until his retirement in 1944. By then, the diagram bearing his and Russell's names had become one of astronomy's essential tools. It remains so today. Modern astronomers may use exquisitely precise measurements from spacecraft such as Gaia, sophisticated stellar models, and computers capable of analyzing millions or billions of stars. Yet one of the first things they can do with those measurements is remarkably familiar: plot luminosity against temperature or color. The patterns Hertzsprung helped recognize more than a century ago immediately appear.

Why It Matters: Ejnar Hertzsprung helped reveal that stars are not a random assortment of lights but members of physically meaningful populations. The Hertzsprung-Russell diagram became one of astronomy's fundamental tools, allowing astronomers to connect a star's temperature and luminosity with its size, age, and evolutionary state. It transformed stellar classification into a way of understanding the lives of stars.

 

Also on This Day

1992 — Pioneer Venus Orbiter Sends Its Final Transmission

19:22 UTC

On October 8, 1992, a spacecraft that had been designed to operate around Venus for less than a year sent its final message home. It had survived for almost fourteen years. NASA's Pioneer Venus Orbiter, also known as Pioneer Venus 1, had launched in May 1978 and entered orbit around Venus on December 4 of that year. It became the first American spacecraft to orbit Venus. The mission was originally expected to operate for approximately one Venusian rotation—about 243 Earth days. Instead, Pioneer Venus continued observing the planet year after year. Venus presents a particularly difficult problem for planetary scientists. Its surface is hidden beneath a global layer of thick clouds. Visible-light telescopes cannot simply photograph its mountains, plains, and other surface features from orbit. Pioneer Venus therefore carried radar. By transmitting radio waves through the clouds and measuring the echoes returning from the surface, scientists could begin reconstructing the topography below. The spacecraft eventually mapped most of Venus within the latitudes accessible to its radar. Its observations revealed an enormous landscape of plains, highlands, mountains, and other geological structures. Among the most prominent was Maxwell Montes, the highest mountain range on Venus, rising roughly 11 kilometers above the planet's mean surface level. But Pioneer Venus was much more than a radar mapper. Its instruments studied the planet's atmosphere, clouds, ionosphere, magnetic environment, and interaction with the solar wind. The spacecraft helped establish that Venus lacks a strong intrinsic global magnetic field comparable to Earth's. That difference matters. Earth's magnetic field carves out a vast magnetosphere around our planet. Venus instead interacts much more directly with the stream of charged particles flowing outward from the Sun. Pioneer Venus repeatedly crossed the resulting boundaries and allowed scientists to study that interaction over many years. Its ultraviolet observations revealed changing patterns in Venus's cloud tops. Other measurements investigated the composition and structure of the upper atmosphere. The spacecraft also detected evidence associated with lightning in the Venusian atmosphere. Its longevity created another scientific advantage. Fourteen years of observations allowed researchers to study Venus through changing conditions in the solar cycle. A mission intended to provide a snapshot became a long-term observatory. By the early 1990s, another NASA spacecraft had arrived. Magellan entered Venus orbit in 1990 carrying a much more sophisticated radar system and began mapping the planet at dramatically higher resolution. Pioneer Venus was no longer alone. But the older spacecraft continued working. Mission controllers used its dwindling propellant carefully, adjusting its orbit and allowing it to descend progressively closer to the upper atmosphere. Those final low-altitude passes provided measurements from regions the spacecraft had not previously sampled. Eventually, there was no propellant left to maintain the orbit. At 19:22 UTC on October 8, 1992, NASA received Pioneer Venus Orbiter's final transmission. Soon afterward, the spacecraft entered the dense Venusian atmosphere and was destroyed. A mission designed for roughly eight months had lasted almost fourteen years.

Why It Matters: Pioneer Venus Orbiter transformed knowledge of Earth's nearest planetary neighbor through long-term measurements of its atmosphere, clouds, plasma environment, and hidden surface. Its extraordinary longevity allowed scientists to observe Venus across much of a solar cycle, turning a short planned mission into one of the enduring successes of early planetary exploration.

 

The Bigger Picture

October 8 brings together two very different ways of understanding distant objects. Hertzsprung could not travel to a star. Pioneer Venus could travel to Venus. That difference illustrates one of the central divisions within astronomy and space science. For the stars, distance forces us to become extraordinarily skilled at interpreting light. From a point of light, astronomers can determine temperature. From spectral lines, they can infer chemical composition. From brightness and distance, they can calculate luminosity. From patterns among millions of stars, they can reconstruct stellar evolution. Hertzsprung helped demonstrate the power of putting those measurements together. A star's position on the H-R diagram tells a story. For planets within our own solar system, however, humanity eventually gained another possibility. We could send instruments there. Venus had been observed from Earth for thousands of years. Telescopes showed its phases. Spectroscopy provided clues about its atmosphere. Radar observations from Earth penetrated its clouds. But spacecraft such as Pioneer Venus could make sustained measurements from the planet itself—orbiting above its atmosphere, repeatedly sampling its environment, and transmitting the results home. These two methods are not competitors. They are parts of the same scientific process. Astronomy teaches us how much can be learned from a distance. Space exploration allows us, where possible, to go closer and test what we think we know. There is another connection between the two events. Both depended upon finding patterns over time. Hertzsprung found order among apparently different stars. Pioneer Venus survived long enough to watch Venus interact with a changing Sun over much of a solar cycle. A single observation can reveal something important. A collection of observations can reveal a system. And systems are what science ultimately seeks to understand. The H-R diagram turned thousands of stars into a coherent story of stellar lives. Fourteen years at Venus turned countless measurements into a changing portrait of a planet. October 8 therefore reminds us that one of the great powers of astronomy is not merely seeing farther. It is learning how to recognize order in what we see.

At a Glance

1873 — Time unknown — Ejnar Hertzsprung is born near Copenhagen, Denmark; his work relating stellar color, temperature, and luminosity will help produce the Hertzsprung-Russell diagram, one of the fundamental tools of stellar astronomy.

1992 — 19:22 UTC — NASA receives the final transmission from Pioneer Venus Orbiter after nearly fourteen years of observations around Venus, ending a mission originally designed to last only about eight months.

October 7

Humanity Sees the Other Side of the Moon

1959 — Luna 3 Photographs the Far Side of the Moon

First photograph: 03:30 UTC

On October 7, 1959, humanity saw a landscape that had remained hidden throughout all previous human history. It was the other side of the Moon. At 03:30 UTC, the Soviet spacecraft Luna 3 began photographing the lunar far side. The accomplishment was remarkable not simply because of the distance involved, but because of a fundamental characteristic of the Moon's motion. The Moon rotates on its axis. But it takes approximately the same amount of time to rotate once as it takes to orbit Earth once. This condition, called synchronous rotation, causes nearly the same lunar hemisphere always to face Earth. Small oscillations known as libration allow observers to see somewhat more than half of the lunar surface over time. But a large portion of the Moon remained permanently hidden from direct observation on Earth. Generations of astronomers could map craters, mountains, and dark volcanic plains on the familiar lunar face. No telescope, regardless of its power, could look around the Moon and show what lay beyond its edge. To see the far side, humanity would have to send a camera there. Luna 3 did exactly that. The spacecraft had launched on October 4 and swept past the Moon's southern polar region on October 6. Its trajectory then carried it behind the Moon and outward, placing its cameras in position to look back at the illuminated far hemisphere. At 03:30 UTC on October 7, from a distance of roughly 63,500 kilometers from the lunar surface, the photographic sequence began. Over approximately 40 minutes, Luna 3 exposed 29 photographs. Together they covered about 70 percent of the Moon's far side. Taking the pictures was only the first challenge. There were no digital cameras. Luna 3 used photographic film. The spacecraft therefore contained an automated miniature photographic laboratory. After exposure, the film was chemically developed, fixed, dried, and then scanned electronically. The resulting image information could be transmitted toward Earth by radio. It was, in effect, a photographic laboratory and long-distance image transmitter traveling through deep space. Seventeen usable photographs were eventually received on Earth. By modern standards, they were poor. They were grainy. Contrast was limited. Fine surface details were difficult to distinguish. But their scientific importance did not depend upon photographic beauty. For the first time, human beings could see enough of the hidden hemisphere to recognize its large-scale geography. And the far side contained a surprise. It looked different. The familiar Earth-facing hemisphere contains enormous dark regions known as maria—ancient impact basins later flooded by basaltic lava. These broad plains create many of the patterns people have imagined as a “Man in the Moon.” The far side showed far fewer large maria. Instead, much of it appeared bright, rugged, mountainous, and densely cratered. Among the features visible in Luna 3's photographs was a dark region later named Mare Moscoviense—the Sea of Moscow. Other features received names as astronomers began constructing the first maps of the newly revealed hemisphere. Later lunar spacecraft would greatly improve upon Luna 3. Zond probes photographed additional territory. American Lunar Orbiter spacecraft mapped potential Apollo landing regions and other portions of the Moon. Apollo astronauts saw the far side directly as they traveled around the Moon. Modern spacecraft such as the Lunar Reconnaissance Orbiter have mapped the entire lunar surface at resolutions Luna 3's engineers could scarcely have imagined. Those later observations revealed one of the solar system's largest impact structures—the enormous South Pole-Aitken basin—spanning much of the lunar far side. Scientists also came to understand why the two hemispheres differ so strongly. The Moon's crust is generally thicker on the far side. On the near side, enormous ancient impacts penetrated more deeply and were followed by extensive volcanic flooding, producing the dark maria visible from Earth. The far side experienced a different geological history. But before scientists could explain that difference, they first had to discover it. Luna 3 provided the first glimpse. The achievement becomes even more remarkable when placed in chronological perspective. Only two years and three days earlier, Sputnik 1 had become the world's first artificial satellite. Now a spacecraft had traveled to the Moon, passed behind it, automatically photographed an unseen world, developed the pictures onboard, and begun the process of returning those images across hundreds of thousands of kilometers of space. The Space Age was barely two years old. Already, humanity had seen beyond the horizon of another world. Why It Matters: Luna 3's photographs gave humanity its first view of the Moon's far side and revealed that the two lunar hemispheres are strikingly different. The mission transformed an entire hemisphere from an unknowable region into a place that could be photographed, mapped, named, and scientifically investigated. It also demonstrated sophisticated deep-space navigation, automatic photography, onboard film processing, and long-distance image transmission at the very beginning of the Space Age.

 

Also on This Day

2008 — Asteroid 2008 TC3 Strikes Earth Exactly Where Astronomers Predicted

Atmospheric entry approximately 02:46 UTC

Before dawn on October 7, 2008, a small asteroid entered Earth's atmosphere over northern Sudan. Such events are not unusual. Small objects from space enter the atmosphere regularly, most burning up harmlessly before reaching the ground. This event was different. Astronomers knew it was coming. For the first time, an asteroid had been discovered in space before an Earth impact and its arrival time and location successfully predicted. The story began only about 20 hours earlier. At 06:39 UTC on October 6, astronomer Richard Kowalski, working with the Catalina Sky Survey's 1.5-meter telescope on Mount Lemmon in Arizona, detected a rapidly moving object. The observations were sent to the Minor Planet Center. Orbital calculations quickly produced an extraordinary conclusion. The object was on a collision course with Earth. It received the designation 2008 TC3. The asteroid was tiny by planetary-defense standards—only a few meters across. It posed no serious threat to people on the ground. But scientifically, it presented an unprecedented opportunity. Observatories around the world began tracking it. During the hours before impact, professional and amateur astronomers supplied hundreds of positional measurements, allowing scientists to refine the asteroid's trajectory. NASA's Jet Propulsion Laboratory calculated that it would enter Earth's atmosphere above northern Sudan at approximately 02:46 UTC on October 7. And it did. The asteroid struck the atmosphere at roughly 12.8 kilometers per second. At high altitude above the Nubian Desert, it exploded in a brilliant fireball. For a time, scientists thought the object might have been completely destroyed. Then came another remarkable development. Meteor astronomer Peter Jenniskens joined Muawia Shaddad of the University of Khartoum and Sudanese students and researchers to search the predicted fall area. They found meteorites. Eventually, hundreds of fragments were recovered from the Nubian Desert. The meteorites became known collectively as Almahata Sitta, Arabic for “Station Six,” after a nearby railway stop. Scientists could now do something unprecedented. They had astronomical observations of an asteroid while it was still in space. They also possessed physical pieces of that same asteroid in laboratories on Earth. The connection between asteroid astronomy and meteorite science had become direct. Analysis revealed that 2008 TC3 was compositionally unusual, containing a diverse mixture of materials associated with a rare meteorite type known as ureilites. The event also demonstrated the rapidly improving capabilities of near-Earth-object surveys. A small asteroid had been found only hours before impact, yet the international astronomical community had been able to determine where and when it would arrive. Larger hazardous asteroids are generally detectable at much greater distances, potentially providing far more warning. Why It Matters: 2008 TC3 was the first asteroid discovered and tracked in space before its impact with Earth was successfully predicted. The subsequent recovery of meteorites linked telescopic observations of a specific asteroid directly with laboratory samples, while the accurate impact forecast demonstrated an important capability for modern planetary defense.

 

The Bigger Picture

October 7 brings together two events separated by nearly half a century. At first they seem unrelated. Luna 3 looked outward toward the Moon. Astronomers tracking 2008 TC3 looked for something coming toward Earth. But both events depended upon the same fundamental ability: predict where an object in space is going to be. Luna 3 could photograph the far side only because engineers understood its trajectory well enough to send it around the Moon and place it in the correct position at the correct time. 2008 TC3 could be predicted to strike northern Sudan because astronomers measured its position repeatedly and calculated its future path. This is celestial mechanics transformed into practical capability. For centuries, astronomers used mathematics to predict where planets would appear in the sky. During the Space Age, those same principles acquired new purposes. They allowed us to send spacecraft toward other worlds. And increasingly, they allow us to identify objects that might come toward ours. The two events also represent different forms of discovery. Luna 3 discovered by seeing something for the first time. 2008 TC3 demonstrated discovery through prediction. Scientists did not merely watch the asteroid appear as a fireball and then reconstruct what had happened. They saw it coming. That distinction is fundamental to planetary defense. Finding an asteroid after it passes Earth tells us about the population of near-Earth objects. Finding one before an encounter gives us options. For an object only a few meters across, as 2008 TC3 was, the appropriate response is observation. For a substantially larger asteroid discovered sufficiently far in advance, the possibilities could eventually include deflection. That is the same planetary-defense story we encountered on September 26 with DART. DART demonstrated that humanity can deliberately change the motion of an asteroid. 2008 TC3 demonstrated another essential part of the equation: first, we must find it and determine where it is going. October 7 therefore spans two very different frontiers. In 1959, an entire hemisphere of the Moon lay beyond human sight. In 2008, astronomers detected a tiny object in the darkness of space and predicted where it would meet Earth. One expanded the world we could see. The other expanded our ability to anticipate what might reach us. Both began by looking carefully into the sky.

At a Glance

1959 — 03:30 UTC — Luna 3 begins photographing the Moon's far side from roughly 63,500 kilometers above the lunar surface, giving humanity its first views of a hemisphere that had never before been seen.

2008 — Approximately 02:46 UTC — Asteroid 2008 TC3 enters Earth's atmosphere over northern Sudan at the location and time astronomers had predicted, becoming the first asteroid discovered before impact whose collision with Earth was successfully forecast.