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.