Monday, October 6, 2014

What Is A Selenelion?

There will be a particularly spectacular lunar eclipse on Wednesday morning. East coast people will catch a glimpse.

What's so special?

A total lunar eclipse happens when the earth sits right between the sun and the moon, preventing sunlight from hitting the moon and then bouncing back. The moon appears red during eclipses because red light is refracted by the Earth's atmosphere and thus some of it still hits. (This was considered a bad omen in many cultures until the phenomenon was understood.

The selenelion occurs when the total eclipse and the rising sun are both visible. This can only happen because of...you guessed it...atmospheric refraction. Refraction shows us the sun slightly before it rises and the moon slightly after it sets. So if you get up before dawn, if the weather cooperates, you may have a 2 to 9 minute "window" in which both are visible. And you might need field glasses to see the moon (obviously don't point them at the sun).

I don't think I'm going to haul myself out of bed that early - there are too many buildings around here anyway. But good luck if you try it.

(A selenelion to me sounds like a lunar werecat).