Finding Celestial Objects

Once your telescope is polar aligned, you must set the hour circle in order to use the measurements listed on the mount to find celestial objects. Once the hour circle is properly set, you will be able to use the coordinates listed on star charts to find objects for viewing in the night sky. Setting the hour circle will require that you recognize and be able to find a star other than the ones used for alignment of the telescope.

SETTING THE HOUR CIRCLE

To set the hour circle, use a star which you are able to easily identify and have the coordinates for. In the Northern Hemisphere, Dubhe is a recogniz- able star which can be used for this. Dubhe is the pointer star in the Big Dip- per closest to Polaris and lies at 58°42’ Dec., 11h23m R.A.. In the Southern Hemisphere, Acrux is an easy to find star for setting the hour circle. Acrux is the closest star to the southern celestial pole in the Southern Cross and lies at -63°15’ Dec., 12h33m R.A..

1.Loosen the declination clamp and rotate the telescope to the nearest de- gree of declination to the star you will be viewing (58° for Dubhe, -63° for Acrux). Retighten the clamp to lock the declination in place.

2.Loosen the right ascension clamp and rotate the telescope on the R.A. axis until the star you are using to set the hour circle is near the center of the finderscope. Retighten the clamp to lock in the R.A. axis.

3.Center the star in the eyepiece using the R.A. and Dec. adjustment cables. Once it is centered, turn the hour circle until the arrow points at the ap- propriate measurement for the star you are looking at (11h23m for Dubhe, 12h33m for Acrux). This sets the hour circle to the appropriate setting for your viewing location and time.

USING SETTING CIRCLES

With the telescope polar aligned and the hour circle set, you can find celes- tial objects using star charts available in books or on the web. A star chart will normally consist of a map and an ephemeris. The ephemeris will tell you the celestial coordinates of an object. By using the hour circle and the declination circle, you can point your telescope at the objects you see on the star chart quickly and easily. You will probably need to fine tune your aiming with the adjustment cables when you view a new star, but the use of celestial coordinates will make finding the objects you would like to look at considerably easier.