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Setting Up Your Telescope

Let us imagine that you have finally obtained your telescope. After spending a few hours assembling it (this can be quite a challenge itself, if the instruction for yours are similar to mine – a literal translation from the Japanese), you see that by some small miracle it is a beautiful, clear night. You lug the telescope out of doors, point it towards your favorite constellation, remove the lens cap and see nothing. What about all those beautiful pictures of the Orion nebulae, Jupiter and the star clusters? First of all, most of those photographs were taken through the world’s largest telescopes. Furthermore, special high-speed film was exposed for several minutes to obtain the best results. You wouldn’t see such magnificent images even if your were looking through the eyepiece of a huge telescope. Now that your expectations are at a slightly more realistic level, shouldn't you be able to see something?

A telescope has an extremely small field of vision, which means it shows only a small area of the sky. The greater the magnification, the smaller the area. The field of vision is very small and the sky is very large. The difficult part of using a telescope is pointing it in the right direction. For instance, my telescope’s field of vision at 50 times magnification barely contains two stars from Orion's belt. Most telescopes have some sort of finder scope. A finder scope magnifies only about five times and points in the same direction as the main scope. When an object appears through the cross hairs of the finder scope, it will also appear in the main scope. Despite the larger field of vision of the finder scope, finding something in a telescope is not always an easy task.

Let us return to the point in time when you just finished assembling your telescope. This is the moment to learn how to use it. Point it out your living-room window and focus on distant objects. Try all the different knobs. Play with the telescope and mount until you feel comfortable using them. Learn about your neighbors. Eventually you will be skygazing in the dark, so it is important to have a "feel" of the instrument and its controls.

To efficiently use an equatorial mounted telescope, it must first be aligned towards the North Celestial Pole. The first steps of alignment are done during daylight. The following instructions are general ones, and your telescope might have its own idiosyncrasies and special knobs. An equatorial mount will have a counterweight hanging from a short metal rod opposite from the telescope tube. Adjust the counterweight and lock it in a position so that the tube moves easily. Even an extremely heavy telescope will move smoothly if the counterweight is adjusted correctly. Now point your telescope towards some distant object, the father the better. Use an object that is relatively small, but can still be easily seen with the assistance of the telescope. This may all be done through an open window. Look through the telescope while using an eyepiece of low magnification. After the image is focused, adjust the telescope so that your distant object is placed in the center of the eyepiece’s field of vision. The object should also now be placed in the center of your finder scope. Most finder scopes have cross hairs to help easily locate their center. Use the thumbscrews of your finder scope to adjust it, if the distant object's image is not located at the intersection of the cross hairs.

The last adjustment will enable you to be sure that if you can locate a star through your finder scope, it will also appear in the much smaller field of vision of the telescope's eyepiece. You will quickly learn that the finder scope's field of vision is none too large either. How do you get it pointed in the right direction? I suppose one solution would be a series of eyepieces each with a narrower field of vision. Then you would just point the telescope in the general direction, center the desired object in the cross hairs of your wide-angle eyepiece and go on to a series of gradually narrowing eyepieces.

A more practical alternative solution is forming a sort of "gun sight" on your telescope. The idea is to place two small, easily-seen upright markers on each end of the telescope tube in such a way that they both line up with the object whose image is in the center of the viewfinder. I improvised my markers from some business cards, which had the proper stiffness and were easy to work with. I first focused the telescope on some distant object. Then, I placed a marker shaped like a small upside down “V” near the tube’s rear. The front-end marker was a square with a similarly shaped but larger “V” drawn on it. I peered through the back marker with one eye towards the distant object and placed the front marker so that both markers and the distant object were all aligned. Improvise any sort of markers that you find comfortable. Only remember that you will be using them in almost complete darkness.

If your telescope is placed on an altazimuth mounting, you're ready to go. On the other hand, if you own an equatorial mount you're probably wondering why, if equatorial mounts are supposed to make it simpler and easier to follow a star’s journey through the sky, the thing looks so complicated. To understand the equatorial mount, we have to back to the celestial sphere. Remember that all stars (and planets during a single night) have a fixed position on the celestial sphere. Every 23 hours and 56 minutes, they each trace a complete circle around Polaris or the North Celestial Pole. The circles are concentric to each other. An equatorial mount enables you to easily follow an object in the sky as it revolves around Polaris. An equatorial mount appears to be complicated because it enables you to move the telescope along three independent axes: polar, declination and right ascension.

The polar axis points the telescope to Polaris and ensures that the concentric circles traced by the telescope match those of the stars. The polar axis of the telescope must be set parallel to the Earth’s axis. The setting of the polar axis can be done once for any particular location. The concentric circles of the celestial sphere are centered around the same point of the sky for any one place on the Earth and need only be changed when shifting locations. If your telescope is in a permanent observatory, its axis is adjusted only once, but if you move it from place to place it must be adjusted before each viewing session. As you go from star to star, there is no need to move the polar axis.

The declination axis points the telescope to the correct concentric circle. The declination of the telescope must be adjusted separately for each object in the sky, unless the object happens to be located exactly on the same circle centered on Polaris.

The right ascension axis points the telescope to the correct point on the concentric circle. Each movement along the right ascension axis directs the telescope to a ray shooting out from the North Celestial Pole. The telescope is directed to the intersection of the ray determined by the right ascension axis and the concentric circle set by the declination axis. Thanks to the movement of the Earth around its axis, a star does not stay at the same point on its concentric circle. The telescope must continually move along the right ascension axis to keep the object in view. A single knob controls the movement. Once the polar and the declination axes are correctly set for a distant object in the sky, only this single knob controlling the right ascension need be twisted as the object moves through the eyepiece’s field of vision.

You are now ready to complete the initial setup of your telescope – the initial adjusting of the polar axis to the North Celestial Pole. First, look up the latitude of your location in an atlas. The number of degrees of north latitude will also indicate the angle between the horizon and Polaris. You must set the polar axis to this angle so that it will point directly toward the North Celestial Pole. The controls for the polar axis are near the mount's base. Hopefully there will be a scale there reading form 0 to 90. If not, you will have to do your initial setting of the polar axis directly as Polaris. After adjusting the polar axis as accurately as possible, clamp it into place. This adjustment should only have to be changed after changing latitude. After going through all that, you will be glad to know that the telescope is now ready to be taken outside.


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