Stargazers are worried about the weather forecast, but if the clouds part in time, Marylanders will get a good look at tonight's total eclipse of the moon - the last one visible here or anywhere until December 2010.
"Baltimore has experienced bad weather for the last few lunar eclipses," said Herman Heyn, Baltimore's original "Streetcorner Astronomer." Both of last year's eclipses were clouded-out here, but if the heavens are visible, Heyn plans to set up at 9 o'clock tonight in the 3100 block of St. Paul St. in Charles Village.
Forecasters were predicting rain or snow before 9 p.m., then partly cloudy skies - perhaps enough to let the moon shine through. Eclipse watchers will have to cross their fingers.
"Astronomers have to be cool about this 'weather-permitting' thing," Heyn said. "Sometimes it seems, as often as not, we're disappointed by the weather, especially around here. Once in a while, we get a break that wasn't predicted."
Behind the clouds or not, at 8:43 p.m., the full moon will begin to slide into the Earth's umbra - the darkest part of the shadow that the planet casts into space.
Gradually, from east to west, the moon's normally brilliant white disk will darken to an eerie reddish or coppery color as sunlight, filtered through all of Earth's sunsets and sunrises, is bent and scattered across the lunar surface.
From 10 p.m. until 10:52 p.m., the moon will be engulfed in the Earth's shadow. It will seem transformed - from the flat-looking white disk we're used to into something unsettlingly ruddy and spherical.
The eclipse will be visible simultaneously throughout the Americas and in Africa, Europe and Central Asia.
After the period of totality ends, the lunar disk will begin to emerge again from the Earth's shadow, becoming fully illuminated again by 12:09 a.m.
If the weather cooperates, this would be the first total eclipse of the moon visible in Maryland - from start to finish - since Oct. 28, 2004. (Last year's were cut short by moonrise or moonset; there were none in 2005 or 2006.) The next one visible here in its entirety wouldn't be until Dec. 21, 2010.
Unlike solar eclipses - which require solar filters or other devices to protect the eyes from the sun's direct rays - lunar eclipses involve only reflected sunlight. They are safe to watch with the naked eye. Binoculars and telescopes are even better.
You can catch the entire spectacle anywhere the moon is visible, but a number of local amateur astronomy groups and observatories are planning public events. They will offer opportunities to see the eclipse, plus a bonus look at Saturn and its rings, through a telescope.
"Saturn will be hovering just a few degrees from the moon, making it unusually easy to spot," Heyn said. "Viewed from Earth, the tilt of the rings varies. ... While their tilt is currently only one-third their maximum, they remain an exciting sight."
Saturn will be the "star" just below the moon, to the left. The true star above the moon is Regulus in the constellation Leo.
The science department at Howard Community College is teaming up with the Howard Astronomical League for a viewing between 8:30 p.m. and 11 p.m. Meet on the roof of the HCC parking garage, 10901 Little Patuxent Parkway in Columbia. For weather updates, visit howardastro.org/eclipse/htm or call 410-772-4891.
A viewing in downtown Baltimore starts at 8 p.m. at the Crosby Ramsey Memorial Observatory at the Maryland Science Center. Visitors can look through any of several telescopes and ask questions of staffers.
"It will be a nice opportunity to catch Saturn in the telescope," said Jim O'Leary, director of the science center's Davis Planetarium. "The rings always bring oohs and aahs from visitors."
"We'll make every effort to be here if there's any chance of a break in the clouds," he said. Call 410-545-2999 after 7 p.m. for weather updates.
The public also is invited to the Maryland Space Grant Observatory on the fourth floor of the Bloomberg Center for Physics and Astronomy at the Johns Hopkins University.
The observatory will be open at 8:30 p.m., if weather permits. Call 410-516-6525 after 5 p.m. for weather updates. For directions, visit www.pha.jhu.edu/~camer cha/openhouse.htm.