Partial Eclipse of Moon Tonight - Questions

Don't know much about astronomy but saw the rise of the partially eclipsed
Moon from the Wiltshire Downs this evening.

The first minute was remarkable in being able to actually see the movement
of the moon through the distant trees.

For the first few minutes there seemed to be a dark line about 10% up from
the lowest part of the Moon - don't know what that was - maybe just a local
cloud?

Initially the Earth's shadow edge was very indistinct - no doubt due to the
atmosphere?

I thought I could see the raggedness around the lower edge of the Moon which
I assumed were mountains. But these seem to disappear as the moon rose
higher and became brighter. So were they mountains or just atmospheric
effects?

As it rose higher it became whiter and brighter and the Earth's shadow edge
sharper. But I thought I could see a bright fringe at the top of the moon?

I can understand that eclipses would only occur at full moon and close to
the equinox when the moon and the sun are in the same plane. But why did the
extent of the eclipse reduce with time and disappear after about an hour?

yours, curious Davy

On Thu, 7 Sep 2006 21:44:58 +0100, "Davy"
wrote:

Don't know much about astronomy but saw the rise of the partially eclipsed
Moon from the Wiltshire Downs this evening.

The first minute was remarkable in being able to actually see the movement
of the moon through the distant trees.

For the first few minutes there seemed to be a dark line about 10% up from
the lowest part of the Moon - don't know what that was - maybe just a local
cloud?

Initially the Earth's shadow edge was very indistinct - no doubt due to the
atmosphere?

I thought I could see the raggedness around the lower edge of the Moon which
I assumed were mountains. But these seem to disappear as the moon rose
higher and became brighter. So were they mountains or just atmospheric
effects?

As it rose higher it became whiter and brighter and the Earth's shadow edge
sharper. But I thought I could see a bright fringe at the top of the moon?

I can understand that eclipses would only occur at full moon and close to
the equinox when the moon and the sun are in the same plane. But why did the
extent of the eclipse reduce with time and disappear after about an hour?

A lunar eclipse occurs when the moon passes into the Earth's shadow.
For this to occur, the moon and sun must be on opposite sides of the
Earth. At this time, the side of the moon we can see is fully
illuminated, hence a full moon. The equinox is not a factor.

In this case, the moon did not completely enter the Earth's shadow but
skirted around the edge. From first contact to max, the amount of the
moon in the shadow increased. After that, more and more of the moon
left the shadow until last contact.

For a reasonable visualization, place a large coin over a small one
with the small one sticking partially out from the bottom. Move one
of the coins laterally and observe how much of the smaller coin is
hidden and how this amount varies with the relative motion.


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