On Friday, June 8, 2001, at 05:27 AM, William R Wood wrote:

> Bill
> Thanks thats exactly what I wanted to know. But your response raised
> another question. Is there a way to turn the drive off without turning
> the
> scope off

Switch to Guide speed and hold down the "E" key. Of course, you'll want
to make the measurement several times and take an average. Fortunately,
in Guide speed holding the "W" key runs the scope at exactly 2x sidereal
rate so you can time the star drifting one way holding E and then time
it the other way with W.



On Friday, June 8, 2001, at 07:56 AM, Paul Markov wrote:

> Just a word of caution about making this kind of timing measurement. A
> few
> nights ago I wanted to do the exact same thing, so I set up the scope in
> alt-az mode without the wedge. Before I turned on the scope for the
> night,
> I found a star within 10 degrees of the celestial equator (ie with a
> declination of +10 deg to -10 deg),

If you're that far from the equator you should divide the result by the
sine of the declination. But it's easier to just fine a star close to
the equator.

> put it on the edge of the field of view
> and started timing the crossing, when the problem appeared! The star
> did
> not cross the field of view thru the center (ie diameter of the field of
> view), rather it crossed diagonally off center, making the test useless.
>
> I attributed this to being set up in alt-az mode.

It doesn't matter whether you're using a wedge or not. With the drive
off the scope stays fixed with respect to the Earth in either case. No
matter what orientation the scope is in a star will drift across the
field along some line. You only need to arrange it so that that line
intersects the center of the field. The easy way to do this is to
center the star in the field and then move it to the edge by going to
Guide speed and pressing E or W.

--
Bill Arnett
http://nineplanets.org/ 37 27 38 N 122 16 11 W
>
>

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