The big astronomical event for May is a total eclipse of the moon on the evening of the 15th. It will be the first of two lunar eclipses this year.
An eclipse of the moon happens when the shadow of the earth falls on the moon. Yes, the earth has a shadow, and we actually live half of our lives within that shadow. We call it night. For an eclipse to happen the sun, the earth and the moon all have to be in a straight line, with the earth in between the other two.
The moon will rise at approximately sunset already eclipsed. If you enjoy photographing celestial events, this eclipse will present an interesting opportunity to get some spectacular shots of the eclipsed moon in juxtaposition with a foreground of your choosing.
The trick will be knowing exactly where the moon is going to rise over the horizon. I will give you a hint. The moon will be in the constellation Libra. So if you are really into this photography thing, go out a couple of nights in advance and find the constellation Libra and see where it is coming up over the horizon.
Why is an eclipsed moon called a “Blood Moon?” When I was a kid learning everything I could about astronomy, nobody had ever heard of the term. Of course the eclipsed moon gets that name because it often turns a strange reddish color.
Why does it look so red? Imagine standing on the moon during an eclipse. You would see the earth blocking the sun. In fact from your perspective you would be witnessing an eclipse of the sun. All around the edges of the earth there would appear to be a ring of fire which would be the combined sunset and sunrise colors all around the earth. That color gets reflected on the surface of the moon, and we see it as the reddish hue.
The moon will be passing almost into the center of the earth’s shadow, which should give it a deep rich hue. Since it will be twilight here when it rises, some of that color may be washed out. We will have to wait and see what it looks like. The totality phase will last about an hour and a half, almost as long as it can get.
Whence the moon?
We all take our moon for granted until it eclipses the sun or is eclipsed itself. Did you know that we have a very unusual moon, the largest in our solar system in comparison to the size of the planet around which it revolves? So how did we get our moon, and where did it come from?
There are several theories about the origin of our moon, but the one currently held in favor is the giant impact theory also known as the “Big Splat.” According to this idea, an object the size of Mars named Theia slammed into the earth about four and a half billion years ago when the solar system was just getting formed. The collision was so violent that the earth and Theia melted and merged together. A little later a big glob spun off to become our moon. Different theories tweak the details a little, but you get the general idea.
If Theia sounds like a mythological name, your hunch is correct. She was a Titan goddess from an older race of gods and was the mother of Selene, goddess of the moon. I am glad that whoever named her was paying attention to mythology.
Since then, the gravity of the earth has slowed the rotation of the moon down to where it has stopped with one side always facing us. The moon is also slowing the rotation of the earth because of the friction of the tides as they slosh back and forth across the ocean beds. A day on the earth used to be just a couple of hours long. How did we ever get anything done?
Did you know that many scientists think that life as we know it would not be possible here without our big moon? That means that we would not be here either. The moon acts like a gyroscope on the earth, steadying our tilt towards the sun. Without that stabilizing force, the earth would be like a wobbly top wandering around all over the place. That would create climate change from hell, making it very difficult for advanced species of life like us to get started here.
If you want to see the planets, you will have to get up early, before the dawn. Venus and Jupiter are the two bright ones, but Saturn and Mars are there too.
Have fun watching the eclipse. It should be spectacular.