University set to host Mercury observation

By Arslaan Arshed
Posted: 11/7/06

When a small black spot moves slowly across the sun Nov. 9, astronomers and casual stargazers will turn out in droves to witness an event that occurs only 13 times per century - and many of them will be viewing it from this campus.

The university was chosen as one of three safe observation areas in the Washington metropolitan area for the transit of Mercury - the passage of its orbit in front of the sun - and will host an observation from 2 p.m. to 5 p.m. on the mall in front of McKeldin library.

Students walking in between classes can have a quick glimpse of the planet 50 to 60 million miles away.

"A Mercury transit is when Mercury passes between the Earth and sun, producing a silhouette," said Michael A'Hearn, a university astronomy professor and principal investigator in the Deep Impact mission in NASA's Discovery Program. "Classically, Venus and Mercury transits were crucial for mapping solar systems. Now they are used to study the atmosphere of planets."

The university was chosen as one of the safest in the area because of the availability of the commercial filters and telescopes. There will be two observing telescopes with filters at the event and one telescope with a camera attached for general viewing.

"You need to have a telescope to see Mercury; you need filters for the sun," said Elizabeth Warner, director of the campus observatory and faculty research assistant who organized the event. "Most people don't have them. You then have the option of going online and buying some or going somewhere to see Mercury."

When looking at the sun, safety is always a major concern. Faculty members recommend not looking into the sun for Mercury with the naked eye or regular sunglasses.

"You need a filter that reduces the sunlight," A'Hearn said. "A regular filter reduces optical light but not infrared and violet. They damage the eye greatly, even causing blindness. So you need special commercial filters to protect yourself, which [the university] has."

According to Fred Espenak, a NASA Goddard Space Flight Center astronomer who has a transit site the last time a Mercury transit occurred was May 7, 2003. The next transit will occur on May 9, 2016. At each transit, the planet travels over a different angle of the sun.

"I think it's important to show people astronomy is actually out there," said Nicholas Chapman, an university astronomy graduate student. "People can look in telescopes and see Mercury itself. It is important to look at the real deal, instead of it on TV. It is a sort of public outreach effort, so people can have a pause."

The Mercury transit is studied heavily to measure the distance and spaces between the planet, earth and the sun.

"You cannot exactly [calculate] with a tape measure, the distance of the sun," said Coleman Miller, a university astronomy professor. "With the Mercury transit, we are participating in an event that is used to measure such distance through mathematics."

Observations will also be held at Montgomery College, on the roof of the King Street parking garage in Alexandria, Va., and on a webcast from Kitt Peak National Observatory in Arizona on

"People for centuries have been taking note of the Venus and Mars transits to understand their place in the universe," A'Hearn said. "Some may think triumph because we can understand the transits, and other may feel humbleness because we look so small compared to the universe. I am not going to constrain views, as long as there are students that are interested."

Contact reporter Arslaan Arshed at

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