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Eclipses (Finally Make It) by Kid. on 2004-09-14 01:19:35

Wash and I were away for a bit, visiting our respective university towns, but were still in regular contact. Also, Skiddy, was whom I first passed on the thought to last week. So, what's bothering me?
Its the size of the moon. In the eclipse - we've all seen them and photos thereof - where the moon goes in front of the sun and blocks it out, the moon is perfectly sized to do it. It is, as we look, exactly the same size as the sun. Why? How crazy is that? I know there are other eclipses but I presume they're from, like, Venus going in front of the sun, not the moon when its further away. I don't know... someone must know if (and if so why) the moon is so perfectly eclipse-efficiently-sized, and if not, well, hey, then no-one does.

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Re: Eclipses (I spent to much time at the Adler Plantarium) by Dr. Sheepwash on 2004-09-14 04:11:17  |  Reply to this
  Okay sorry I didn't explain it in the pub I was too busy talking to the Ginger one. I'll only say this once so here it goes: Not every eclipse of the Sun is a total eclipse. Sometimes, the Moon is too small to cover the entire Sun's disk. To understand why, we need to talk about the Moon's orbit around Earth. That orbit is not perfectly round but is rather oval or elliptical in shape. As the Moon orbits our planet, it's distance varies from 221,000 to 252,000 miles. This 13% variation in the Moon's distance makes the Moon's apparent size in our sky vary by the same amount. When the Moon is on the near side of its orbit, the Moon appears larger than the Sun. If an eclipse occurs at that time, it will be a total eclipse. However, if an eclipse occurs while the Moon is on the far side of its orbit, the Moon appears smaller than the Sun and can't completely cover it. Looking down from space, we would see that the Moon's umbral shadow is not long enough to reach Earth. Instead, the 'antumbral' or negative shadow reaches Earth. The track of the antumbra is called the path of annularity. If you are within this path, you will see an eclipse where a ring or 'annulus' of bright sunlight surrounds the Moon at the maximum phase. An eclipse of the Sun (or solar eclipse) can only occur at New Moon when the Moon passes between Earth and Sun. If the Moon's shadow happens to fall upon Earth's surface at that time, we see some portion of the Sun's disk covered or 'eclipsed' by the Moon. Since New Moon occurs every 29 1/2 days, you might think that we should have a solar eclipse about once a month. Unfortunately, this doesn't happen because the Moon's orbit around Earth is tilted 5 degrees to Earth's orbit around the Sun. As a result, the Moon's shadow usually misses Earth as it passes above or below our planet at New Moon. At least twice a year, the geometry lines up just right so that some part of the Moon's shadow falls on Earth's surface and an eclipse of the Sun is seen from that region. The Moon's shadow actually has two parts: Penumbra - Faint outer shadow; partial eclipses are seen from within this shadow. Umbra- Dark inner shadow; total eclipses are seen from within this shadow. When only the Moon's penumbral shadow strikes Earth, we see a partial eclipse of the Sun from that region. However, if the Moon's dark umbral shadow sweeps across Earth's surface, then a total eclipse of the Sun is seen. The track of the Moon's shadow across Earth's surface is called the Path of Totality. It is typically 10,000 miles long but only 100 miles or so wide. In order to see the Sun totally eclipsed by the Moon, you must be in the path of totality.
Re: Eclipses (Finally Make It) by JohnnyG/Usef Islam otherwiseknownasCatStevens on 2004-09-23 22:19:41  |  Reply to this
  "I'm being followed by a moon shadow, moon shadow, moon shadow" That's a crescent moon shadow I'll have you know. Let me into the USA. I'm forming a "Peace Train". CAT
Re: Re: Eclipses (Finally Make It) by Kid on 2004-09-25 04:21:21  |  Reply to this
  Odd. I was just reading an article in today's Independent about Cat Stevens not being allowed into the US, jocularly suggesting the lyrics to Moon Shadow as a reason
Re: Re: Eclipses (Finally Make It) by JohnnyG on 2004-09-26 00:11:18  |  Reply to this
  I have some wits about, around, beside and inside me Kid. Surprised? My mother always seems to be.