Tuesday, 1 May 2012

How to use telescope setting circles

Due to the current thick clouds overhead i have not been able to do astronomy for a couple of weeks now, this also means that I missed both of the occulations :( . So i have decided to make a post on how to use telescope setting circles. On some telescopes mounts (mainly equatorial) there are 2 dials called setting circles, one of them is called right ascension and the other is declination. These are basically the latitude and longitude of the sky, the declination is the latitude and the right Ascension is the longitude. The setting circles on a telescope are used to easily locate object that aren't easily visible to the naked eye.  Once you have set your telescope up at night you will have to align the right ascension setting circle, but you wont have to align the declination ( if you are using a equatorial telescope make sure that the tilt is set to your latitude, this will have most likely been done when you bought your telescope).

The RA circle is marked in hours and then minutes each hour will have its hour number written next to it. To align the RA setting circle we first need to find an object in the sky for instance Jupiter, you then need to look up its RA for that specific date and time. Once you know that you then turn the RA circle so that the pointer is pointing to Jupiter's (or whatever object your using) current RA, your RA circle is now aligned. Then you find the objects you want to observes RA and declination for instance m42 and slew your telescope until the RA and declination pointers are pointing at the correct degree (declination) and minute (RA). You should then be able to see the object in your eyepiece. To find and object with setting circles it is generally easiest to locate it with a low power eyepiece to give you a wider field of view.

Specific note for skywatcher explorer 130:
If you have this scope you will notice that the pointer for the RA moves with the dial, this shouldn't happen. To fix this once you have aligned your RA circle tighten the screw so that the dial turns with the mount, then you can use the mark in between the R and the A as a pointer.
              This picture shows that the pointer moves with the setting circle for some unknown reason.
The Mark between the R and the A can be used as a a pointer.
I Hope you have found my guide on how to use telescope setting circles, if you have any questions feel free to ask.

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