Transcript
How To Use The 12 Inch Telescope I. Opening Up The procedure for opening the dome is as follows: 1. Unlock the door. The 12" telescope is in the easternmost dome on the 7th floor of Sterling Hall. 2. Light switches are located to the right just inside the door, one for the dome lights, another for the storage area. An additional dome light switch is located at the telescope level, beneath the dome light. 3. Open the dome slit by removing the restraining u-bolt between the slit doors, then by cranking the handle in the lower right hand corner of the slit until it is completely open. 4. Roll back the plastic sheet above the telescope. It is important to do this after opening the slit in order to protect the scope from any debris that might fall inward. 5. Remove the dust covers from the front of the 12" telescope (turn the small knob and pull outward) and from the front of the larger finder. 6. Turn the telescope power on. The switch can be found on the telescope pier on the opposite side from the sidereal clock. 7. Place a low-power, wide-field eyepiece in the 12" telescope. (E.g., the 50mm eyepiece; the larger the focal length given on the eyepiece, the lower the power and the wider the field.) Eyepieces are located in a small wooden box in the dome. 8. Point the 12" telescope to any light on the horizon (see next section for how to move telescope) and find the focus of the eyepiece. Then check the alignment of the finder telescope with the 12". Center the light in the 12" field; the light should be very near the center of the finder field. If not, turn the adjustment screws on the finder mount until the light is on the crosshairs in the finder. Note that the white button on the finder telescope eyepiece holder illuminates the crosshairs when held down. II. Acquiring a Celestial Object or "Pointing the Telescope" The telescope must be manually pointed toward the desired object, after which fine adjustments can be made with the hand paddle. For brighter objects that can be seen with the naked eye, one can simply point the telescope by sighting along the finder telescope. This will usually put the object in the finder field. The object can then be centered on the finder cross-hairs, and if all is aligned the object will be in the field-of-view of the 12" telescope. For objects not visible to the naked eye, you will need to know the right ascension (") and declination (*) of the target in the present equinox. (Note that present coordinates for many objects of interest are given in the Astronomical Almanac.) In addition, the local sidereal time (LST) must be available. A sidereal clock is located in the telescope mount (the upper clock) and should be accurate to within a minute. If you feel that the clock is not set properly, contact one of the graduate students in the class so that it can be corrected. The only subtlety in moving the telescope is the use of the right ascension and declination clutches or locks. When the clutches are released, the telescope is free to be moved by hand; however the clock drive and the hand paddle are not engaged and the telescope will not track a star. When the clutches are tightened, the telescope does not freely move by hand, but the clock drive is engaged and the telescope can be moved (albeit slowly) with the hand paddle. The basic idea is to slew (i.e., move long distances) by hand and set (i.e., fine movements) with the paddle. Given the " and * of the object, follow these steps to acquire it: 1) Set the declination of the telescope to that of the object. a. Point the telescope to the east or west sky, as appropriate. b. Unlock the * clutch (the longer of the two clutches). The telescope should be balanced so that it does not swing on its own when the clutch is released. If it does, contact a graduate student in the class so that it can be corrected.
c. The * setting circle is labeled from 0 to 90 degrees in both directions in intervals of 2E. A vernier scale is also present, labeled from 0 to 2 degrees in intervals of 0.5E. Move the telescope in the direction of the object until the 0 mark on the vernier scale aligns with the mark on the * circle nearest to but less than the desired declination (e.g., for +23E, move the scope until the 0 vernier mark is aligned with +22E.) d. Now, move the telescope north until the additional * needed as indicated on the vernier scale aligns with a mark on the * circle (e.g., for +23E and the vernier 0 mark now lined up at +22E, move the telescope north until the 1E mark on the vernier scale lines up with a mark on the * circle.) e. Lock the * clutch firmly. 2) Set the hour angle of the telescope to that of the object. a. The telescope is pointed in right ascension by setting the hour angle (H.A.) setting circle. To obtain the hour angle of an object, use the following formula: H.A. = LST - " Positive H.A. indicates an object west of the local meridian, negative H.A. an object east of the local meridian. b. Release the H.A. clutch (the shorter one), then position the telescope using the H.A. circle (0 to 12 hours in each direction in intervals of 4 minutes) and the H.A. vernier scale (0 to 4 minutes in intervals of 1 minute.) The procedure is analogous to that for setting the declination. For example, for LST of 18h 12m and an object right ascension of 16h 30m, the hour angle is 1h 42m west. Move the telescope west until the 0 mark on the vernier scale is aligned with the 1h 40m mark on the H.A. circle. Now move further west until the 2m vernier mark lines up with a mark on the H.A. circle. Note that at present the telescope cannot be balanced for all positions in the sky with one setting of the counterweights. If the telescope moves in right ascension by itself, use the crank at the end of the declination axis to balance it. Usually only a few turns will suffice. c. Lock the a clutch firmly (the telescope will not track unless the clutch is locked). 3. Rotate the dome using the 3-button control box. Once a direction is chosen, the dome will continue to rotate until the stop button is pressed. Sometimes the motor will not rotate the dome after a direction button is pressed - move a little in the opposite direction and try again. 4. Locate the object in the field of the finder scope. Once found, place the object in the center of the finder field by using the hand paddle. The hand paddle has four buttons for direction and a speed control (for declination only). If the object is not in the field, make a systematic scan for it by releasing one clutch and moving a field or two either way, then locking that clutch at the original position and doing the same with the other clutch. 5. Repeat (4) with the 12" telescope. Always acquire initially with a wide-field eyepiece and then move up to higher power if warranted. III. Closing Procedures 1. Turn telescope power off. 2. Move the scope in * until it is in a horizontal position. (Lock the clutches.) 3. Replace telescope and finder dust covers. 4. Pull down and secure the plastic sheet above the telescope. 5. Close slit and lock with u-bolt. 6. Record your night in the logbook. 7. Turn off all lights before leaving and make sure the door is locked.
