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Skies Clear for Transit of Mercury

November 15th, 2006

The clouds and fog cleared away just long enough on November 8th to allow students and other interested folks to witness astronomy history at Hartnell College when the planet Mercury crossed in front of the Sun during a five-hour event.

Astronomers from Hartnell and from the Fremont Peak Observatory set up five solar telescopes of various sizes and capabilities on the roof of Hartnellís new parking structure and invited the public to come observe this rare event that occurs roughly 13 times a century.

The transit of Mercury was visible across most of North America, though only people in the western part of the country could see it in its entirety, which lasted from 11:12 a.m. to 4:09 p.m. During the transit, Mercury appeared as a tiny dark disc--only 1/194 the size of the Sun--moving slowly across the Sun.

Andy Newton, director of Hartnellís J. Frederic Ching Planetarium and the organizer of this viewing, was one of the scientists on hand to answer questions about the phenomenon and to assist in the use of the telescopes. Other participating astronomers were Dr. Patrick Donnelly, president of the Fremont Peak Observatory Association (FPOA); Loren Dynneson, a director of the board at FPOA; and Greg Bosler, a local architect and long-time friend of Hartnell.

Whether this was a viewerís first time to use a telescope or the 101st, the sight of Mercury in this rare alignment was a treat. The next transit of Mercury will not occur until May 9, 2016. Confusing some this time was the appearance of a dark sunspot, much larger than Mercury and irregularly shaped.

Among those viewing the transit on Wednesday were students from Dr. Pimol Mothís astronomy class. Moth, who studied for her B.A. in astrophysics at Berkeley before earning a masterís degree and Ph.D. in astronomy at the University of Florida, is the newest member of Hartnellís astronomy faculty.

By afternoonís end, when most students had gone back to the classroom or library, the astronomers had fun discerning how high in the solar atmosphere the telescopes were observing. They timed the appearance of the fourth contact of Mercury (when it passes out of the Sunís face) in white light telescopes and in the Hydrogen alpha telescope. Based on a difference of 50 seconds, Dr. Donnelly was able to calculate that the H-alpha scope was observing 2,623 miles higher in the solar atmosphere than the white light scopes were.

Hartnell College and the Fremont Peak Observatory have a long-standing collaboration that benefits both organizations. Hartnell astronomy students regularly take field trips to the observatory to take advantage of the dark skies 3,000 feet above the valley floor.

Additionally, Newton and Doug Brown, vice president of the FPOA, developed an intern program for Hartnell students so that the students can assist in the public presentations given at Fremont Peak. Students are first trained on the use of the 30-inch Challenger telescope and in interpretation of the night sky. Then they work with mentors to develop plans for their public presentations or observing sessions. The Challenger telescope is one of the largest astronomical instruments in the world whose primary purpose is public education in astronomy.