Thursday, June 22, 2017

Journey to the Shadow, No. 5

Trivia: The Total Solar Eclipse of January 1, 1889, also known as the New Year’s Day Eclipse of 1889.

The path of totality began in the Bering Sea, crossed the North Pacific Ocean, passed through California to the north of San Francisco, through northern Nevada, Idaho, northwestern Wyoming, Montana, the northwestern part of North Dakota, and into central Canada, passing through southern Manitoba, and finishing on the western edge of Ontario.

The first photograph of a solar eclipse was taken during solar eclipse of July 28, 1851. But even with this technological advancement, most of the recorded observations of a total solar eclipse remained in the form of the written word and drawings. For the January 1, 1889 eclipse, a group of amateur and professional astronomers joined forces with a new photography society in San Francisco. They agreed to combine their resources to observe and record the eclipse. One example of the efforts was a photographic plate on which multiple exposures were made, showing many partial eclipse phases leading to totality.

On February 7, the group reunited in downtown San Francisco and presented their observations. The group enjoyed the experience so much that they agreed to form their own astronomical society, called the Astronomical Society of the Pacific (ASP). Originally a society of forty members, the ASP has grown to a national society dedicated to astronomy education and outreach. The ASP helps people of all ages learn astronomy and helps those people share their knowledge with others.

You can learn more about the ASP at the society’s official website:


Wednesday, June 21, 2017

Journey to the Shadow, No. 4

Today, representatives from NASA, other federal agencies, and science organizations, will provide important viewing safety, travel and science information on the August 21 total solar eclipse. This eclipse will be the first in 99 years that will cross the entire continental United States.

Two briefings will be held at the Newseum in Washington starting at 1 p.m. EDT. The briefings will air live on NASA Television and stream on the agency’s website.

Over the course of 100 minutes, 14 states across the United States will experience more than two minutes of darkness in the middle of the day. Additionally, a partial eclipse will be viewable across all of North America. The eclipse will provide a unique opportunity to study the sun, Earth, moon and their interaction because of the eclipse’s long path over land coast to coast. Scientists will be able to take ground-based and airborne observations over a period of an hour and a half to complement the wealth of data and images provided by space assets.

Today's briefings are:

Logistics Briefing 1 to 2 p.m. EDT

Thomas Zurbuchen, associate administrator of NASA’s Science Mission Directorate at the agency’s headquarters in Washington

Vanessa Griffin, director of the National Oceanic and Atmospheric Administration’s Office of Satellite and Product Operations in Suitland, Maryland

Brian Carlstrom, deputy associate director of Natural Resource Stewardship and Science at the National Park Service in Washington

Martin Knopp, associate administrator of the Office of Operations in the Federal Highway Administration at the U.S. Department of Transportation in Washington

Science Briefing: 2:30 to 3:30 p.m. EDT

Thomas Zurbuchen

Angela Des Jardins, principal investigator of the Eclipse Ballooning Project at Montana State University, Bozeman

Angela Speck, professor of astrophysics and director of astronomy at the University of Missouri, Columbia

Dave Boboltz, program director of solar physics in the Division of Astronomical Sciences at the National Science Foundation in Arlington, Virginia

Linda Shore, executive director of the Astronomical Society of the Pacific in San Francisco

Matt Penn, astronomer at the National Solar Observatory in Tucson, Arizona

The panels will take questions from media participating in person and by phone. The public also can ask questions via social media during the briefings using #eclipse2017.

For NASA TV streaming video, schedule and downlink information, visit:

For more information on the eclipse, and how to safely view it, visit:


Thursday, May 18, 2017

Saturn's Shortening Shadow

Saturn's shadow across the rings, as seen from the Cassini spacecraft. Image Credit: NASA/JPL-Caltech/Space Science Institute

The Cassini spacecraft continues sending back great images and data during the Grand Finale portion of its mission at Saturn. Here we see a sign of the changing seasons at Saturn, in that the planet’s shadow across the rings is shortening.

The above image was taken at a distance of about 760,000 miles (1.2 million kilometers) from Saturn. The image scale is 46 miles (73 kilometers) per pixel.

To learn more, read the full article here.


Wednesday, April 26, 2017

Cassini's Big Finish Begins

Saturn eclipsing the sun, seen from behind by the Cassini orbiter. Earth can be seen as a small dot between the rings on the upper, left-hand side. Image Credit: NASA/JPL/Space Science Institute

(My apologies for the "big finish." But because the other phrase is so prevalent, I just had to find something to say other than "grand finale,” at least once.)

The NASA Cassini mission is winding down, quite literally. On April 26, the Cassini spacecraft became the first to dive between Saturn and its ring system. This begins the spacecraft’s “grand finale” in which it will make 22 amazing orbits and, on September 15, enter Saturn’s atmosphere and burn up. The spacecraft will be useful until the very last moment–it will be sending back data continuously, including measurements of the composition of Saturn’s atmosphere, rotation rate and interior structure.

Until that time, the instrument teams have several new observations to make. These include understanding a Saturn radiation belt, discovered inside the rings in 2004, and taking close-up pictures of the rings and other features.

Read the 2004 Article: New Radiation Belt

The spacecraft will also image Saturn’s cloud tops at close range, weigh its ring system (which will indicate just how old it is), sample the atmosphere of the planet and its rings, and measure Saturn’s internal structure.

Read the NASA PDF Resource on the Mission (published 1997)

Originally called Cassini-Huygens, the mission involves ESA, NASA and the Italian Space Agency. The idea of the mission began in 1982, when the European Science Foundation and the American National Academy of Sciences formed a working group to investigate future cooperative missions. Two European scientists suggested a paired Saturn Orbiter and Titan Probe as a possible joint mission. In 1983, NASA's Solar System Exploration Committee recommended the same Orbiter and Probe pair as a core NASA project. NASA and the European Space Agency (ESA) performed a joint study of the potential mission from 1984 to 1985. ESA continued with its own study in 1986, while American astronaut Sally Ride, in her 1987 report, also examined and approved of the Cassini mission.

In 1988, NASA Associate Administrator for Space Science and Applications Len Fisk wrote to his counterpart at ESA, Roger Bonnet, strongly suggesting that ESA choose the Cassini mission from the three candidates at hand and promising that NASA would commit to the mission when ESA did.

Read the Article: Launch of Cassini Spacecraft

On October 15, 1997, a Titan IVB/Centaur rocket launched from Cape Canaveral Air Force Station in Florida, sending the Cassini orbiter and its Huygens probe on a seven-year, 2.2-billion mile journey to the Saturn system.

Read About the Spacecraft

The mission arrived at Saturn on July 1, 2004. The mission was originally planned for four years. But Cassini-Huygens was so successful that the mission multiple times, eventually to 2017. It has flown past seven of the larger satellites, including giant Titan – which is larger than the planet Mercury. The orbiter passed Titan more than 70 times. Flying within 880 km of the moon, it studied Titan’s orange clouds and nitrogen-rich atmosphere. It also mapped its surface with an imaging radar.

On Christmas Day 2004, Huygens separated from Cassini. Three weeks later, it entered Titan’s thick atmosphere, becoming the first probe to land on the surface of a planetary satellite (other than Earth’s moon). Protected by a heat shield, the probe slowed from 18,000 to 1,400 km per hour in just three minutes. Soon after, a large parachute opened. At a height of about 160 km, the probe began to take pictures and study the atmosphere. For more than two hours, data from Huygens were received and stored on Cassini as it flew overhead.

Read More

To learn more about Cassini, Huygens, Saturn, Titan, the rest of the Saturn system, and the Grande Finale, check out these links.

Read About the Mission

See the Mission Timeline

Read the FAQ for Cassini – The Grand Finale

Read the 2017 Article: Bittersweet feeling as Cassini mission embarks on its ‘grand finale’ ahead of death plunge

Read the 2014 Article: Cassini 10 Years at Saturn Top 10 Discoveries

Read the 2017 April Article: Cassini Completes Final -- and Fateful -- Titan Flyby


Tuesday, April 04, 2017

Journey to the Shadow, No. 3

or-bit (ˈȯr-bət) noun. 1. a. A path described by one body in its revolution about another (as by the earth about the sun or by an electron about an atomic nucleus); also, one complete revolution of a body describing such a path. b. A circular path[Middle English, from Medieval Latin orbita, from Latin, rut, track, probably from orbis]

An orbit is a regular, repeating path that one heavenly body takes around another body. A body which orbits another body is a satellite of the other body. So, the moon is a satellite of Earth, while at the same time, Earth is a satellite of the sun, along with the other planets, comets, asteroids, and many other bodies in the solar system. And remember that the sun orbits the center of our Milky Way galaxy. So, the sun is a satellite of the Milky Way.

A satellite can be classified as natural or artificial. The moon, Earth and other heavenly bodies are natural satellites. All orbiting objects made by humans are artificial satellites. The first artificial satellite was Sputnik 1, launched in 1957. A more recent example is the International Space Station, which was launched in pieces and assembled in orbit.

Most orbiting bodies move along or close to an imaginary flat surface. This imaginary surface is called the ecliptic plane.

What Shape Is an Orbit?

Orbits come in different shapes. All orbits are elliptical, which means they are the shape of an ellipse, similar to an oval. For the planets, the orbits are almost circular. The orbits of comets have a different shape. They are highly eccentric or "squashed." They look more like thin ellipses than circles.

Satellites that orbit Earth, including the moon, do not always stay the same distance from Earth. Sometimes they are closer, and at other times they are farther away. The closest point a satellite comes to Earth is called its perigee. The farthest point is the apogee. For planets and other bodies that orbit the sun, the point in their orbit closest to the sun is perihelion. The farthest point is called aphelion. Earth reaches its aphelion during summer in the Northern Hemisphere. The time it takes a satellite to make one full orbit is called its period. For example, Earth has an orbital period of one year. The inclination of an orbit is the angle the orbital plane when compared with Earth's equator.

This diagram of an Earth orbit demonstrates an elliptical orbit and shows apogee, perigee, aphelion, and perihelon. Image Credit: NOAA

How Do Objects Stay in Orbit?

An object in motion will stay in motion unless something pushes or pulls on it. This statement is called Newton's first law of motion. Without gravity, an Earth-orbiting satellite would go off into space along a straight line. With gravity, it is pulled back toward Earth. A constant tug-of-war takes place between the satellite's tendency to move in a straight line, or momentum, and the tug of gravity pulling the satellite back.

An object's momentum and the force of gravity have to be balanced for an orbit to happen. If the forward momentum of one object is too great, it will speed past and not enter into orbit. If momentum is too small, the object will be pulled down and crash. When these forces are balanced, the object is always falling toward the planet, but because it's moving sideways fast enough, it never hits the planet. Orbital velocity is the speed needed to stay in orbit. At an altitude of 150 miles (242 kilometers) above Earth, orbital velocity is about 17,000 miles per hour. Satellites that have higher orbits have slower orbital velocities.


Sunday, April 02, 2017

Journey to the Shadow, No. 2

e-clipse (i-ˈklips) noun. 1. a. The total or partial obscuring of one celestial body by another. b. The passing into the shadow of a celestial body. Compare OCCULTATION, TRANSIT. [Middle English, from Anglo-French, from Latin eclipsis, from Greek ekleipsis, from ekleipein to omit, fail, suffer eclipse, from ex- + leipein to leave]

An eclipse happens when one heavenly body, such as a moon or planet, moves into the shadow of another heavenly body. There are two types of eclipses as seen from Earth: an eclipse of the moon and an eclipse of the sun.

An eclipse of the moon...

The moon moves in an orbit around Earth, and at the same time, Earth orbits the sun. Sometimes Earth moves between the sun and the moon. When this happens, Earth blocks the sunlight that normally is reflected by the moon. Instead of light hitting the moon’s surface, Earth's shadow falls on it. This is an eclipse of the moon—a lunar eclipse. A lunar eclipse can happen only when the moon is full.

A lunar eclipse can be seen from Earth at night. There are two types of lunar eclipses: total lunar eclipses and partial lunar eclipses.

A total lunar eclipse happens when the moon and the sun are on exact opposite sides of Earth. Although the moon is in Earth's shadow, some sunlight reaches the moon. The sunlight passes through Earth's atmosphere, which causes Earth’s atmosphere to filter out most of the blue light. This makes the moon appear red to people watching from Earth.

A partial lunar eclipse happens when only a part of the moon enters Earth's shadow. In a partial eclipse, Earth's shadow appears very dark on the side of the moon facing Earth. What people see from Earth during a partial lunar eclipse depends on how the sun, Earth and moon are lined up.

A lunar eclipse usually lasts for a few hours. At least two partial lunar eclipses happen every year, but total lunar eclipses are rare. It is safe to look at a lunar eclipse.

A lunar eclipse. Image credit: NASA

An eclipse of the sun...

Sometimes when the moon orbits Earth, it moves between the sun and Earth. When this happens, the moon blocks the light of the sun from reaching Earth. This causes an eclipse of the sun, or solar eclipse. During a solar eclipse, the moon casts a shadow onto Earth.

There are three types of solar eclipses. The first is a total solar eclipse. A total solar eclipse is only visible from a small area on Earth. The people who see the total eclipse are in the center of the moon’s shadow when it hits Earth. The sky becomes very dark, as if it were night. For a total eclipse to take place, the sun, moon and Earth must be in a direct line.

The second type of solar eclipse is a partial solar eclipse. This happens when the sun, moon and Earth are not exactly lined up. The sun appears to have a dark shadow on only a small part of its surface.

The third type is an annular (pronounced “ANN-you-ler”) solar eclipse. An annular eclipse happens when the moon is farthest from Earth. Because the moon is farther away from Earth, it seems smaller. It does not block the entire view of the sun. The moon in front of the sun looks like a dark disk on top of a larger sun-colored disk. This creates what looks like a ring around the moon.

A solar eclipse. Image credit: NASA

During a solar eclipse, the moon casts two shadows on Earth. The first shadow is called the umbra (pronounced “UM-bruh”). This shadow gets smaller as it reaches Earth. It is the dark center of the moon’s shadow. The second shadow is called the penumbra (pronounced “pe-NUM-bruh”). The penumbra gets larger as it reaches Earth. People standing in the penumbra will see a partial eclipse. People standing in the umbra will see a total eclipse.

The umbra and penumbra. Image credit: NASA

Solar eclipses happen approximately once every 18 months. Unlike lunar eclipses, solar eclipses only last for a few minutes.

You should never look directly at the sun. It can permanently damage your eyes. You must use proper safety equipment to look at any type of solar eclipse. More on this later.


Monday, March 27, 2017

Journey to the Shadow, No. 1

On August 21, millions of people will look skyward to witness a spectacle not seen in 38 years—a total eclipse over the continental United States. This time, the shadow will span the continental U.S. from coast to coast, the first to do so since 1918. Even those in the U.S. who will not be in the path of totality, will see a partial solar eclipse.

The August 21 eclipse might be the most viewed sky event in history. The Sun’s shadow will travel from Oregon to South Carolina. In addition, the shadow will pass over thousands of miles of the Pacific and Atlantic oceans. But the shadow will touch no other land.

This will be the first total solar eclipse to cross the continental United States in 38 years. One eclipse did pass over Hawaii in 1981. But the last for the continental U.S. was February 26, 1979. Sadly, few saw it because observers had to be in one of only five states in the northwest, and the wintry weather was bad along the path of totality.

Before the 1979 eclipse, there was the eclipse of March 7, 1970. That eclipse passed up the U.S. east coast. More people directly saw that eclipse than the 1979 eclipse, but because that was 47 years ago, few in the United States are still with us who saw the 1970 total eclipse with their own eyes.

For August 21 total eclipse, I plan to add my name to the list of those who have seen a total eclipse for themselves. I plan to stand in the path of totality and experience night in the daytime. Along the way, I will review the phenomenon which we call solar and lunar eclipses. I will recount the history, delve into the mythology, and try to separate the fact from fiction. This is just my first step. Join me on my journey to the shadow.