Re: accuracy with planetary pointing


Roland Christen
 

In a message dated 8/16/00 3:09:07 PM Central Daylight Time,
terry@venus.sunquest.com writes:

<<
But I'm trying to understand the situation here. It sounds like you'd be
jiggering the *civil* time to help with planetary position calculations,
and that makes no sense to me.>>

Yes, of course, but "civil time" is not accurate when it comes to stellar
time. Civil time can be off by as much as 1/2 hour if you are located near
the edges of your time zone. Further more, in the case of Europe, some
countries have chosen to be in the wrong time zone. In their case, at 12 noon
"civil time" the sun is 2 hours off the meridian in the summer, and 1 hour
off in the winter. If you use this civil time, then the calculated zenith
crossing faithfully recreates this 1 hour discrepancy. There is no way
around, except to adjust the time zone and clock time to correspond to what
is actually happening on the sky.

In the case of the US mainland, the most you will be off with the meridian
swap would be about 1/2 hour at the edges of the time zones. This applies
ONLY to the meridian swap, has nothing to do with the pointing accuracy of
the mount. That is fixed by your initial synchronization on a known star. We
always know where any other point in the sky is, because the distances are
known and fixed.

Roland Christen

>>I would have thought you'd just tell the mount its latitude and longitude,
set its clock to Universal Time, align it, >>

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