Seek transit glory with view of Mercury and sun

Safe sightings available at science center and on the Web

November 07, 2006|By Frank D. Roylance | Frank D. Roylance,Sun reporter

The planet Mercury is lining up for a rare, five-hour passage across the face of the sun tomorrow afternoon - the last until 2016.

No need to rush outside. You can't see it directly without a safely filtered telescope. But the Maryland Science Center has a couple of them, and it will host a sun-safe viewing for the public from its rooftop observatory and from the Harborplace promenade.

This "transit of Mercury," as it's called, will also be Webcast.

Why the excitement? "It's like an eclipse - sort of a meeting of heavenly bodies in front of us ... and we get to watch it for ourselves at the predicted time and place," said Jim Leary, director of the science center's Davis Planetarium.

Through a telescope with a proper solar filter, Mercury will look like a tiny black BB, creeping across the bottom quarter of the sun's bright disc. It will begin the trek about 2:12 p.m., and complete it at 7:08 p.m. But the last anyone in Maryland will see of it will be when the sun sets - at 4:58 p.m. in Baltimore, about halfway through the transit.

If skies are clear, paying visitors to the science center will have an opportunity to watch through the telescope in the Crosby Ramsey Memorial Observatory, through smaller telescopes set up on the roof, or via monitors in the SpaceLink display.

Passersby will have free access to several portable telescopes on the promenade.

Until the sun sets behind neighboring buildings about 4:15 p.m., O'Leary said, "we'll have a leisurely couple of hours" to watch the transit, weather permitting.

The event will be visible in its entirety for residents of the West Coast, Alaska and Hawaii, New Zealand and the Pacific Islands. The Far East will catch the end of the show at sunrise on the 9th, local time.

It will also be observed by NASA's Solar and Heliospheric Observatory (SOHO), and Transition Region and Coronal Explorer (TRACE) satellites; by telescopes at the Kitt Peak National Observatory in Arizona; the University of Hawaii's observatories on Mauna Kea; and others.

This is the first Mercury transit since May 7, 2003, and only the 10th since World War II. For some, it may recall the transit of Venus on June 8, 2004. The first since 1882, it was barely visible without magnification, but still drew hundreds of Marylanders to the science center for a look.

Mercury and Venus are the only planets whose transit of the sun can be seen from Earth because they're the only ones that orbit between the sun and us. Mercury is just 36 million miles from the sun (compared with Earth's 93 million miles), and circles it once every 88 days.

To get a closer look, NASA's Messenger spacecraft is now on course for Mercury. It's scheduled for its first flyby June 5 - only the second spacecraft in history to make the trip. In March 2011 it will drop into orbit around the planet, ready to send back photographs and scientific data.

The Messenger mission is being run for NASA by the Johns Hopkins University's Applied Physics Laboratory near Laurel.

Scientists have spread out from Arizona to Hawaii to carry out a variety of transit experiments.

Williams College astronomer Bryce Babcock and Kevin Reardon of Italy's Arcetri Observatory will try to use Mercury's trek across the sun's face to measure and map the sodium in its tenuous atmosphere - also a key objective for Messenger.

"This is going to inform what Messenger is going to do," said Williams eclipse expert Jay Pasachoff, who arrived on Maui yesterday for the transit. "It's all the more important that it comes soon, before we get closer observations from Messenger."

Similarly, scientists are using observations of tiny Mercury as it crosses the sun to improve their techniques for detecting new planets as they orbit in front of distant stars and slightly dim their light.

"A couple of years ago [during the transit of Venus] we detected the drop in the total brightness of the sun by a tenth of a percent," Pasachoff said. "Because Mercury is smaller [than Venus] and because it's more than twice as far away ... we'll be particularly interested to see if we can pick up this event."

Mercury moves between the Earth and the sun about once every 116 days, but normally passes just above or below the sun's disc as seen from our perspective.

Mercury transits occur either in May or November. The November transits occur at intervals of 7, 13 or 33 years.

Transits of Venus come in pairs. The second Venus transit of the current cycle is due June 6, 2012. But the following cycle won't begin until Dec. 11, 2117.

A Frenchman named Pierre Gassendi - acting on a prediction by Johannes Kepler - was the first to watch a Mercury transit, in 1631. He safely projected the sun's light through a telescope onto a sheet of paper.

Even if tomorrow's events at the Maryland Science Center are canceled by cloudy weather, the transit will be Webcast by:

The Exploratorium, the museum of science in San Francisco, at

NASA, at http:--sunearth The NASA Webcast will include commentary by Messenger's deputy project scientist, Deborah Domingue.

The University of Hawaii, at Transit06.html.

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