« Almost Live From the Front Lines | Main | So You Like Planets? »
More Red Moons than a Baboon
The Solar System >
At long last we get to experience a cosmic event from the comfort of our home, live from the Moon. This Thursday night the Moon will vanish, only to return again hours later in a sky show called a lunar eclipse.
Just as a way of reminder, the lunar eclipse differs from its more famous and glitzy brother, the solar eclipse. In a solar eclipse, the Moon moves between the Sun and us; we are in Moonshadow then.
This Thursday, however, things are turned around. We are between the sun and moon; we are the ones casting a big shadow on our Little Orbiting Buddy.
Now you may be thinking: Why doesn't this phenomenon happen all the time? The Moon goes around us all year, and every month at Full Moon it's on the opposite side as the sun. Shouldn't the Moon go through our huge shadow much more often?
It's a little more complicated than that. First, the Moon isn't always on the exact same plane as the sun. Sometimes it moves over our shadow just missing it, sometimes it ducks below. So although every month it goes over to where our shadow is, most of the time it misses going through it.
Second, our shadow is a big one, to be sure, but the Moon is one great distance away --- over 230,000 miles out there. Put in perspective, if the Earth were the size of a big grapefruit and the Moon were a golfball, the Moon would be over 200 golfballs away, over 15 feet. The odds of getting that golfball into the shaft of the grapefruit's shadow aren't exactly overwhelming.
But it does happen. And when it does it is a beautiful thing. Here are some things to watch for.
By the time the Moon rises Thursday, it is already in the shadow, so unfortunately we will miss the covering up sequence. But! We can see it uncover throughout the evening.
During the 8 o'clock hour go out and look to the east. If it is a clear sky, you'll notice that as the sun is setting behind you, a great purplish "horizon" will be rising into the sky in front of you. This great arc of rising darkness is the shadow of the Earth streaming out into space. From that darkness you'll see the Moon emerge, by now already fully in the shadow.
If the conditions are right, as the Moon rises it will appear a ruddy copper color. Why, if it's in shadow? Although we cut off the Sun's light to the Moon, our atmosphere is getting into this act.
Our atmosphere can actually bend light like a giant lens. While the blue side of the light spectrum gets scattered pretty easily --- the reason for blue sky --- the red light can make it through.
A person on the Moon during a lunar eclipse sees Earth as a black ball rimmed with a thin red circle of light, an "all-over sunset" if you will. Out atmosphere focuses this red light towards the Moon and reddens it.
In the late 9 o'clock hour you'll see an historic phenomenon. As the Moon passes slowly in its orbit from darkness to light, you'll see the edge of the Earth's shadow is curved. It is always curved, and always has been. Why is this historic? The Greeks, thousands of years ago, noticed this and came to the conclusion that the Earth was the shape that always makes a curved shadow --- a sphere. Yes, ancient people knew the world was round! Clever people, those Greeks.
Until next time, clear skies and happy lunar eclipse!
Mark Ritter teaches astronomy at Temecula Valley High School and can be reached at mritter@firstlightastro.com.
Photo Credit & Copyright: Fred Espenak (courtesy of www.MrEclipse.com)
Posted by Administrator at 2003.05.10 01:35 PM | Comments (0)
