Re: Anyone shoot the eclipse?

On Sat, 23 Feb 2008 16:39:44 -0700, "Roger N. Clark (change username
to rnclark)" <username@xxxxxxxxx> wrote:
The moon rotates in the sky with the rotation of the earth.
From our point of view on the earth, the moon rotates as it moves
across the sky with respect to our local horizon.
For example, when the moon is rising, the north
pole of the moon would point approximately to the left
in an image, but would point to the right when it is setting
(from the northern hemisphere).

If you put your camera on a motor driven equatorial mount and point it
at the moon, you don't have to worry about the moon rotation causing
blur because it rotates at the same rate as it orbits. If the north
pole of the moon is on the left of your image frame as the moon rises,
it will still be on the left of your image frame as the moon sets.

However, if you want to get technical, the moon does have variations
in it's presentation to an observer on earth so that it's not
*exactly* in the same orientation all the time. The part of the moon
we see varies over the course of a month and even over the course of
an evening. It's called lunar libration. But that's a long term
effect and certainly doesn't effect short time exposures, on the order
of seconds or even minutes. It's nothing like the motion blur you get
if the camera is stationary and your exposure is a couple of seconds.
See http://en.wikipedia.org/wiki/Libration

Steve
.

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