In the dark and very cold hours before dawn Tuesday, the brilliant full moon will slide into the long shadow the Earth casts into space, progressively dimming to what might become an eerie copper color.
It's a total lunar eclipse, the first visible anywhere since February 2008 and, if the weather cooperates, the last Marylanders will see until April 2014.
"There's something a bit magical about it," said Jim O'Leary, director of the Maryland Science Center's Davis Planetarium. "It's sort of the dance of the heavenly bodies. And to watch something we have absolutely no control over, we're fascinated by it, as people have been for centuries."
The eclipse will begin for Marylanders at 1:32 a.m., as the moon's sunlit disk begins to slide into the Earth's shadow. From the moon's lower left, the dark shadow will appear slowly to engulf the moon, finally swallowing it all at 2:41 a.m., as the eclipse becomes total.
Mid-eclipse will be around 3:17 a.m., and the moon will begin to re-emerge from the shadow, beginning to brighten again at its upper left side, at 3:53 a.m. And at 5 a.m., it will be back in full sunlight, and the eclipse will be over.
Unlike a solar eclipse, lunar eclipses are perfectly safe to watch without eye protection. Binoculars or small telescopes might even enhance the experience of watching the Earth's shadow creep across the moon's craters and highlands.
The science center is planning to offer visitors — those willing to brave the cold and risk a sleepless night — a view from the center's Crosby Ramsey Memorial Observatory.
Besides the classic telescope under the dome — a 1927 Clark 8-inch refractor — visitors will have a selection of smaller telescopes out on the roof deck to peek through. Science center guides will be on hand to explain what's going on and answer questions.
"Maybe it will be a little bit warmer than it's been for the last few days," O'Leary said. The doors will open Tuesday morning at 1:30 a.m., and the observation will continue until 5 a.m. Call 410 545-2999 to check for cancellation because of the weather.
So far, the forecast looks pretty good. The National Weather Service predicts partly cloudy skies Monday night, with a partly sunny day on tap Tuesday. But it will be a cold vigil. Overnight lows will be in the mid-20s, about average for this time of year.
One of the most striking and unpredictable things about lunar eclipses is the color of the eclipsed moon.
"Whether it's black or gray or shades of orange depends on what the sunlight is doing," O'Leary said.
Once the moon is in full shadow, it can be almost totally black. The moon emits no light of its own, so while it's in shadow it might receive almost no sunlight at all to reflect back to the observer's eyes. "One year, the moon was impossible to find when it was in total eclipse," O'Leary recalled.
More often, however, the sunlight streaming through the Earth's atmosphere is filtered through volcanic dust and air pollution, giving it the brown, orange or coppery color of all the planet's sunrises and sunsets – a "ring of fire" around the night side of our planet as seen from the moon.
Then that light is refracted, or bent onto the lunar surface, bouncing back to our eyes with a similar hue.
"You never know what to predict," O'Leary said. The color is "a compilation of the whole Earth's atmosphere, or at least what's around the rim."
Another curious feature of a total lunar eclipse is the slightly curved edge of the Earth's shadow where it crosses the moon's face. It is the clue that enabled even some of the ancients to surmise that the Earth itself was round.
O'Leary said it's hard to predict how many people might venture out on a school or work night to stand in the cold and watch the eclipse.
During a partial solar eclipse at mid-day on a cold Christmas Day in 2000, he said, "we had 425 people show up. It was a great event." Other celestial events have drawn "several dozen to several hundred."
But this one is special, he said. "We won't see another [total lunar eclipse] for three-and-a-half years; and it could be cloudy three-and-a-half years from now."
Of course, unless you're seeking a communal experience, there's no need to venture into downtown Baltimore in the middle of the night. The eclipse will be easily visible anywhere in North America where skies are clear.
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