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Rare Winter Solstice Lunar Eclipse Late Tonight

The eclipse will begin at 1:32 a.m. and become a total eclipse at 2:40 a.m, reaching its peak at 3:16 a.m.

Elizabeth Jeffery, Ph.D., is an astronomer and researcher at the Space Telescope Science Institute in Baltimore City.

This year's only total eclipse of the moon will be seen over the Baltimore area late tonight, so if you're not a night owl, set your alarm.

The eclipse will begin at 1:32 a.m. and become a total eclipse at 2:40 a.m, reaching its peak at 3:16 a.m. The National Weather Service predicts a low of 23 degrees, so be sure to dress warmly.

Of course, if it's cloudy, as the NWS also predicts, we may not be able to see the eclipse. Clouds are the natural enemy of the astronomer, so let's hope for clearer skies.

This is a rare occurrence in which a lunar eclipse is happening on the winter solstice, the first day of winter and the shortest day (or the longest night) of the year. This is also when the moon will be at its highest in the sky during the night, which makes for good viewing of the eclipse.

So, what is a total lunar eclipse?  

During a total lunar eclipse, the full moon passes completely within the shadow of the earth. This is different from a solar eclipse which occurs when the moon blocks out part or all of the sun. A lunar eclipse lasts much longer than a solar eclipse because it takes much longer for the moon to pass through the earth's large shadow than for the moon to cross the sun.  

Think of it this way: The sun and the moon have roughly the same angular size—that is, if you extend your arm to the sky and measure the size of them between your fingers, the sun and the moon are about the same size—and so, when the moon and sun align from our point of view on earth, the moon won't be able to block it for very long. The moon is always moving!

It's safe to view a lunar eclipse without protective eye wear for two main reasons. First, the moon is not as bright as the sun (moonlight will never damage your eyes as much as sunlight); and second, during a lunar eclipse, the moon will appear fainter than normal and even easier on the eyes.

We're familiar with shadows and how an object's shadow has the same shape as the object itself. When the moon first starts entering the shadow of the earth, the shadow that is cast on the moon is curved. This is proof that the earth is round and not flat. We take this fact for granted today, but it's actually historically important and interesting.

Perhaps the most interesting part of watching a lunar eclipse is the color during totality (that is, when the moon is completely within the shadow). The moon will appear darker and have a slight reddish color to it. This happens because light from the sun is refracted (bent) by the atmosphere of the earth. Blue light is scattered away and red light dominates. This is the same reason sunsets and sunrises are red. The exact shade of red will depend on how much dust is in the atmosphere.

The eclipse will happen in stages. It begins with the point of first contact when the moon begins to enter the earth's shadow.  As the moon continues to move across the sky, eventually it will be completely within the earth's shadow. We call this totality. It will then begin to exit the shadow and continue on its way until it appears normally. When you go out to watch it, make sure you know what you're getting into. For example, if you just want to see it in totality, you'll have to wait if you go outside as soon as the eclipse starts.

Lunar eclipses can only happen during a full moon. This is because the alignment of the sun-earth-moon system is required for an eclipse is the same that is required for a full moon. We don't have a lunar eclipse during every full moon because the moon's orbit is slightly tilted relative to earth, so it usually misses the earth's shadow during the full moon.

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