(SOUNDBITE OF SONG, "MOONDANCE")
AUDIE CORNISH, HOST:
It's must-see astronomy tonight across most of the U.S. A full lunar eclipse, as the moon moves into the Earth's shadow and turns a lovely shade of red. It's a blood moon, and it's actually the first of four full lunar eclipses that will occur in the next 17 months. Joining me to talk about this is Fred Espenak. He runs NASA's eclipse website and he does that from Portal, Arizona. Welcome to the program.
FRED ESPENAK: Hello.
CORNISH: So a lunar eclipse, I guess, is not that unusual but having a series of them is. When was the last time that happened?
ESPENAK: Well, the last time we had four total lunar eclipses in a row was back in 2003 and 2004. Of course, they weren't all visible from the U.S. The interesting thing about the tetrad, as they're called - where you have four total lunar eclipses in a row - is that all four of them can be seen from various parts of the United States.
CORNISH: So walk us through it. What are we going to see tonight or in the wee hours of Tuesday morning?
ESPENAK: Well, from the East Coast, the partial eclipse begins at 1:58 a.m. The moon's disc will slowly start edging its way into the Earth's amble shadow. And to the naked eye, you'll see a little bite being taken out of the moon. That will gradually grow larger and larger over the course of an hour. And by 3:07, the total eclipse takes place. That's when the moon will exhibit those brilliant red and orange colors and that lasts for about 72 minutes. And then it's followed by another hour of partial phases. And the whole show ends at 5:33, just as it's time to get up and go to work.
CORNISH: Now, you mentioned those brilliant red and orange colors, help us understand what shade of red the moon will be. I mean, what are the possibilities and the cause for the color?
ESPENAK: Well, the colors are actually hard to predict exactly. When the moon is totally inside the Earth's shadow, the Earth is blocking all direct sunlight from the moon. But the moon is still illuminated because sunlight filters through the atmosphere of the Earth and is bent in the direction and illuminates the moon in this red color. What's happening is the sunlight that filters through Earth's atmosphere, most of the blue and green light is scattered away, just as you see at sunset and sunrise, you get those red colors. You might think of it as the fact that the moon is being illuminated by all the sunrises and sunsets around the world simultaneously.
CORNISH: Lastly, Fred Espenak, what kind of view are you going to have from Portal, Arizona, and how will you be celebrating this eclipse?
ESPENAK: Well, I'm not going to be doing any kind of science. I'm just going to be photographing it for the fun it and just enjoying the beautiful show, because we really understand all the mechanics behind lunar eclipses and there's not much research involved left for eclipses. So, most astronomers are off busy studying things like black holes and quasars and things like that, and lunar eclipses are right here in our backyard and they happen quite frequently. And most astronomers aren't particularly interested in them.
CORNISH: Oh, man. So you guys are like blase about it, like we're all getting excited.
ESPENAK: Well, I'm excited about it.
CORNISH: OK, good. That's Fred Espenak. He runs the eclipse website for NASA. He spoke to us about tonight's lunar eclipse. Thanks so much for talking with us.
ESPENAK: Thanks a lot. Transcript provided by NPR, Copyright NPR.