Évaluations - 3, GPA: 4.7 ( )

Fabricant : Celestron Taille : 274.67 kb Nom Fichier : Langue d'enseignement:

There are several methods of polar alignment, all of which work on a similar principle, but are performed somewhat differently. For 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 northern hemisphere all stars appear to move around the north celestial pole (see figure 6). When the telescope’s polar axis is pointed at the celestial pole, it is parallel to the Earth’s rotational axis. Many of the methods of polar alignment require that you know how to find the celestial pole by identifying stars in the area. For those in the northern hemisphere, finding the celestial pole is not difficult. Fortunately, we have a naked eye star less than a degree away. This star, Polaris, is the end star in the handle of the Little Dipper. Since the Little Dipper (technically called Ursa Minor) is not one of the brightest constellations in the sky, it may be difficult to locate, especially from urban areas. If this is the case, use the two end stars in the bowl of the Big Dipper. Draw an imaginary line through them toward the Little Dipper. They will point to Polaris. The position of the Big Dipper will change during the year and throughout the course of the night. When the Big Dipper is low in the sky (i.e., near the horizon) it may be difficult to locate. Figure 6 Figure 7 To make finding and tracking the stars easier, a rough polar alignment is required. 1. The right ascension (polar) axis should be pointed towards the North Pole (see figure 7). 2. The equatorial mount should be level. 3. Set the latitude of the telescope to the latitude of your observing location by turning the azimuth adjustment screws (#14) on the mount. The latitude of your observing location corresponds to the altitude that Polaris will appear to be above the horizon. For example, If you are observing from Los Angeles, which has a latitude of 34°, then the celestial pole (and Polaris) will be 34° above the northern horizon. All a latitude scale does then is to point the polar axis of the telescope at the right elevation above the northern (or southern) horizon. 4. Release the DEC clamp 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. 5. Using the altitude and azimuth adjustment screws (#14 & #20), move the mount until Polaris is in the field of view of the finderscope. Rough adjustments in azimuth can be made by moving the tripod. 6. Center Polaris using the altitude and azimuth controls. Remember, do not move the telescope in R.A. and DEC. You want to adjust the direction the polar axis is pointing and you are using the telescope to see where the polar axis is pointing. This gets you close to the pole but not directly on it. In order to improve your accuracy for more serious observations and photography Celestron offer an optional Polar Axis Finderscope (#94221) that fits into the polar axis of the mount. Aligning the R.A. Setting Circle Before you can use the setting circles to find objects in the sky you need to align the R.A. setting circle. The declination setting circle is aligned during the process of polar alignment. In order to align the R.A. setting circle, you will need to know the names of a few of the brightest stars in the sky. If you don’t, they can be learned by using the Celestron Sky Maps (#93722) or consulting a current astronomy magazine. To align the R.A. setting circle: 1. Locate a bright star near the celestial equator. The farther you are from the celestial pole the better your reading on the R.A. setting circle will be. The star you choose to align the setting circle with should be a bright one whose coordinates are known and easy to look up. 2. Center the star in the finderscope. 3. Look through the main telescope and see if the star is in the field. If not, find it and center it. 4. If you purchased an optional motor drive, start it now so that it will track the star. 5. Look up the coordinates of the star. 6. Rotate the circle until the proper coordinates line up with the R.A. indicator (the zero mark on the vernier scale). The R.A. setting circle should rotate freely. NOTE: Because the R.A. setting circle does NOT move as the telescope moves in R.A., the setting circle must be aligned each time you want to use it to find an object. This holds true even if you are using an optional motor drive. However, you do not need to use a star each time. Instead, you can use the coordinates of the object you are currently observing. Once the setting circles are aligned you can use them to find any objects with known coordinates. The accuracy of your setting circles is directly related to the accuracy of your polar alignment. 1. Select an object to observe. Use a seasonal...

Téléchargez votre

Pour télécharger, entrez 2 chiffres :