Celestron Omni CG-4 Telescope Mount Astronomy Basics - Page 5

Sigma Octantis is visible. Sigma Octantis has a magnitude of 5.5 and may be difficult to see and a binocular may be helpful as well as the finderscope. 1. Set the telescope up so that the polar axis is pointing south. 2. Loosen the DEC clutch knob and move the telescope so that the tube is parallel to the polar axis. When this is done, the declination setting circle will read 90°. If the declination setting circle is not aligned, move the telescope so that the tube is parallel to the polar axis. 3. Adjust the mount in altitude and/or azimuth until Sigma Octantis is in the field of view of the finder. 4. If the above is done correctly, you should be able to observe near the pole through the finderscope and a low power eyepiece. Remember, while Polar aligning, do NOT move the telescope in R.A. or DEC. You do not want to move the Sigma Octanis S.C.P. Southern Cross telescope itself, but the polar axis. The telescope is used simply to see where the polar axis is pointing. Like the previous method, this gets you close to the pole but not directly on it. Finding the South Celestial Pole (SCP) This method helps improve your polar alignment and gets you closer to the pole than the above methods. This will improve your accuracy for more serious observations and photography. In each hemisphere, there is a point in the sky around which all the other stars appear to rotate. These points are called the celestial poles and are named for the hemisphere in which they reside. For example, in the southern hemisphere all stars move around the south celestial pole. When the telescope's polar axis is pointed at the celestial pole, it is parallel to the Earth's rotational axis. Many methods of polar alignment require that you know how to find the celestial pole by identifying stars in the area. Observers in the southern hemisphere are not as fortunate as those in the northern hemisphere. The stars around the south celestial pole are not nearly as bright as those around the north celestial pole. The closest star that is relatively bright is Sigma Octantis. This star is just within naked eye limit (magnitude 5.5) and lies about 1° from the south celestial pole but can be difficult to locate. Therefore, with this method, you will use star patterns to find the south celestial pole. Draw an imaginary line toward the Omega Octanis Alpha Centauri Beta Centauri Beta Crucis Alpha Crucis S.C.P. SCP through Alpha Crucis and Beta Crucis (which are in the Southern Cross). Draw another imaginary line toward the SCP at a right angle to a line connecting Alpha Centauri and Beta Centauri. The intersecting of these two imaginary lines will point you close to the south celestial pole. Declination Drift Method of Polar Alignment This method of polar alignment allows you to get the most accurate alignment on the celestial pole and is required if you want to do long exposure deep-sky astrophotography through the telescope. The declination drift method requires that you monitor the drift of selected stars. The drift of each star tells you how far away the polar axis is pointing from the true celestial pole and in what direction. Although declination drift is simple and straight-forward, it requires a great deal of time and patience to complete when first attempted. The declination drift method should be done after any one of the previously mentioned methods has been completed. To perform the declination drift method you need to choose two bright stars. One should be near the eastern horizon and one due south near the meridian. Both stars should be near the celestial equator (i.e., 0° declination). You will monitor the drift of each star one at a time and in declination only. While monitoring a star on the meridian, any misalignment in the east-west direction is revealed. While monitoring a star near the east/west horizon, any misalignment in the north- south direction is revealed. It is helpful to have an illuminated reticle eyepiece to help you recognize any drift. For very close alignment, a Barlow lens is also recommended since it increases the magnification and reveals any drift faster. When looking due south, insert the diagonal so the eyepiece points straight up. Insert the cross hair eyepiece and align the cross hairs so that one is parallel to the declination axis and the other is parallel to the right ascension axis. Move your telescope manually in R.A. and DEC to check parallelism. First, choose your star near where the celestial equator and the meridian meet. The star should be approximately within 1/2 an hour of the meridian and within five degrees of the celestial equator. Center the star in the field of your telescope and monitor the drift in declination. • If the star drifts south, the polar axis is too far east. • If the star drifts north, the polar axis is too far west. Make the appropriate adjustments to the polar axis to eliminate any drift. Once you have eliminated all the drift, 5