Sky's Up July-September 2017 - Page 14

1 10 ? s As a professional astronomer at NASA’s Jet Propulsion Laboratory and a committed amateur astronomer at home and at his California observatory, Steve Edberg has witnessed countless celestial spectacles. Even with this constant bombardment of new astronomical experiences, his decades-long fondness for eclipses has never dulled. “My first recollection of seeing a solar eclipse is of the total eclipse that crossed Alaska, Canada and the extreme northeastern U.S. in July 1963,” Edberg said. “My family was visiting Chicago at the time, and I just couldn’t convince anyone to make the 800-mile drive to the path of totality. Instead, I just saw the deep partial eclipse there.” Since that fateful day, the self-proclaimed avid eclipse chaser has organized viewing expeditions and observed 16 total eclipses from land, sea and air; five annular eclipses; numerous partial eclipses; and a wide variety of other 14 COURTESY OF Steve Edberg JPL’s Steve Edberg shines a light on our favorite star transitory events involving stars, planets and asteroids. “The ‘action’ in the sky, the alignment and the spectacular views attract me to these events and the others related to total eclipses,” he said. “The only similar events with the suspense and adrenaline rush were landings of the space shuttle that I’ve seen at Edwards Air Force Base and Kennedy Space Center. In his professional capacity at JPL, Edberg has worked on a variety of NASA projects including the Galileo mission to Jupiter and the Cassini mission to Saturn. He has served as Coordinator for Amateur Observations for the International Halley Watch and was executive director of the Riverside Telescope Conference, Inc. for 22 years. He also has been honored by the International Astronomical Union with the formal naming of the asteroid 1985QQ as (3672) Stevedberg. In this installment of 10 Questions, Edberg discusses eclipse phenomena and solar science. Sky ’ s Up No and Yes. Only Earth is treated by its natural satellite, the Moon, appearing large enough to just cover the Sun without covering much of the sky around the Sun. Some other planets see the Sun “over-covered” or way “under-covered” by some or all of their natural satellites. Were you to visit any of these places to observe these events, they would look very different from a total eclipse on Earth. If you are interested in the differences and the details, read on. It is first helpful to learn about eclipse and related phenomena here on Earth so you can understand what is described when viewing the events visible on other planets. Eclipse Types and the View from Earth The Moon is the only natural satellite in the Solar System that closely matches the apparent size of the Sun in the sky when viewed from the host planet’s surface (or cloud tops, for gas planets). So, on average, every 1.5 years the Moon will pass in front of the Sun having its apparent size just slightly larger than the Sun. When it blocks the full disk of the Sun, we say we are having a total solar eclipse. Depending on the separation of Earth and Moon and Earth and Sun, a total eclipse can last as long as about 7-1/2 minutes and as short as instantaneous, being total for only a split second. You usually won’t hear both of the following two eclipse descriptions described as partial eclipses, but they really are. A partial eclipse occurs when the Sun is not completely covered by the Moon. This situation is more common over time because the Moon spends more time farther from Earth than closer to Earth on its elliptical orbit each month. Every eclipse has a partial phase, the only difference In this recurring feature, Sky’s Up gives students the opportunity to ask 10 Questions to leading astronomers, space explorers, scientists and cosmologists. o o o The questions for this installment were submitted by students at Truman Middle School in St. Joseph, Mo. Solar power Can solar eclipses be seen on other planets? Sky ’ s Up COURTESY OF Steve Edberg This image shows the Sun’s in ner (“lower”) corona during the total eclipse of March 29, 2006, visible from al Saloum, Egypt. Here the Moon has completely covered the Sun, plunging the area and sky into darkness. During this time, the silvery, gossamer corona makes its appearance. This image shows a partial solar eclipse visible from La Canada High School on October 23, 2014. The whole image was too large for the camera sensor so it was cropped to present part of the crescent and the large sunspot group together. This sunspot group is much larger than Earth and is dark because it is 2000C cooler than the surrounding 6000C white light layer that shines on us daily. The silhouette of the Moon is much blacker than the sunspots; the sunspots are still emitting light but not as brightly as their surroundings. Notice the mountains and valleys visible along the edge of the Moon’s silhouette. COURTESY OF Steve Edberg 15