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RA, DEC and Setting circles.

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I've sort of got my head around setting circles, but something is baffling me.

If I have levelled and polar aligned my scope, and set my DEC to 90 degrees, then surely no matter what I do with RA, polaris should be within my fiend of view (sort of), so why is Polaris's RA listed as 2h 31min 48,7sec? Why not zero (or close to it)?

BTW... aren't the setting circles on the EQ3-2 just the flakiest things in the world? :)

Edited by pook
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Every star, deep sky object, and planet, sun and moon has a Right Ascension and declination. Stars and deep sky stuff keep their RA as to all intents and purposes, they are fixed. Although most have a proper motion, they are so far away, that motion is not discernible.

The Moon and planets move in their orbits, and their RA and Declination changes on a daily basis. The more distant ones, very slowly. If you want to find the coordinates of a solar system object, you must consult an Ephemeris, which is a Yearly publication.

Stars and Deep Sky, as I said, keep the same Ra and Declination.

Polaris has the Ra 2h 31m 48.7 secs. If you place your telescope on Polaris, and the drive is running at Sidereal rate, then Polaris will remain in the eyepiece as long as the drive is accurate.

Your scope when set to sidereal rate, is effectively a Sidereal Clock.

If your circles were big enough, and properly indexed, , All you need to do, is locate a star of known RA and Declination, set your circles accordingly, switch on your scope drive, and you can then locate anything in the Sky you wish. As long as it is in the sky to be found. You effectively have a Goto telescope.

Star Atlases change star coordinates every 50 years, known as an Epoch. The changes reflect the differences, due to the proper motions of objects that have changed position.


Edited by barkis
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I worried about this when I got my first EQ mount aswell.

Turns out I never use them, for me it is much easier to familiarise myself with some charts, a telrad finder and do a few 'star hopps'

Whether that is a good or bad thing I don't know. But as long as I can find things with relative ease and quickly i'm happy :)


Good luck!


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