Wednesday, August 22, 2007

Lunar Eclipse Advice

If you're not too familiar with lunar eclipses, here's some good advice to keep in mind if you're planning to observe next week's event. Number one: staring at a lunar eclipse for too long will cause you to go blind. Just kidding. (But can you believe that that's apparently enough of a misconception that NASA feels it's worth speaking to, on their eclipse website?)

Here's the real advice, with elaboration below each point:

1. You want to see the Moon when it's in the umbra, not the penumbra.

There are two parts to any shadow, and this includes the one cast by the Earth: there's the lighter, outer shadow (called the penumbra) and the darker, inner shadow (called the umbra). The effect of Earth's penumbral shadow being cast on the Moon is extremely subtle. So subtle, in fact, that I guarantee you won't notice it. So if you're checking a time table for the lunar eclipse, you'll want to make sure you find out when the Moon first comes into contact with the umbra, not the penumbra. Otherwise you'll find yourself sitting there for over an hour waiting for anything appreciable to occur. I say this out of personal experience (I once went to some length to pack my telescope and drive far out into the country for a "total" lunar eclipse, only to learn that some "total" lunar eclipses are entirely penumbral, i.e. hardly noticeable. Absurdly, this means that there are some partial lunar eclipses more worthwhile than total ones!)

2. To observe this eclipse, you're gonna need an alarm clock, a pot of coffee, and, if you're east of the Pacific Time Zone, a tolerance for slight unfulfillment.

For locations in North America this Tuesday's lunar eclipse occurs in the early morning hours. In fact, for everywhere except the Pacific Coast, the umbral eclipse is beginning in the pre-dawn hours, as the Moon is approaching moonset. Now I don't mean to discourage anyone from trying to go out to see it (quite the contrary!)... it's just that I want to issue this disclaimer, lest I get anyone's hopes up:

Unless you live far out in the Pacific Ocean, you're going to have to get out of bed real early. Additionally, the further east of the Pacific that you live, the lower in the sky (and closer to the time of sunrise) the eclipse event is going to occur, and the Moon will actually set while the eclipse is still in progress.

3. If you own a pair of binoculars, or a small telescope, use it.

But, that said, if you don't, don't fret. Your naked eyes will do just fine.

4. For your convenience:

Here's the time schedule, culled from NASA's Total Lunar Eclipse of Aug. 28, 2007 webpage for when the Moon approximately begins to enter the umbral shadow, and when it completely leaves it:

Eastern Daylight Time: Begins to enter at 5:52 am; completely leaves by 7:22 am
Central Daylight Time: Begins to enter at 4:52 am, completely leaves by 6:22 am.
Mountain Daylight Time: Begins to enter at 3:52 am; completely leaves by 5:22 am.
Pacific Daylight Time: Begins to enter at 2:52 am; completely leaves by 4:22 am.

As I said, for most observers the moon will set while the eclipse is in progress. But if you're curious, you can find Moon- (and Sun-) rise and set data by entering your location and the date (Aug 28) in the following form available at the U.S. Naval Observatory's Complete Sun and Moon Data for One Day.

5. You're not crazy if you do in fact get out of bed to go watch this.

Who cares what your boss thinks about the bags under your eyes? You directly observed the sphericity of the Earth, man! You saw the light of the sum of all sunrises and sunsets! You're one of those rare lovers of the world and all its splendid phenomena!

6. But you are kind of crazy...

You lunatic! I mean did you notice the time tables above--that's insanely early! And it's a worknight, no less! Lunar eclipses are not so rare that it's not like you won't have another chance in your life to see some more, blah blah blah...

(I leave it to your speculation to decide where I'll be early Tuesday morning.)

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