H. B. Prosper and J. Skofronick, 2-Oct-2001, AST1002 L
I.
FINDING
POLARIS
A.
Examine
the telescope looking at all of the controls; see Fig.
1. You have: the main
telescope with the 25 mm eyepiece, the finder scope, the azimuth and the
altitude locks, the Declination (Dec), the Right Ascension (R.A.) and the
motor drive with control lever. The
telescope is already mounted on the tripod.
You should ask someone to help you adjust it to a comfortable
height. There is a
bubble at the center of some of the tripods which should be centered before
continuing with the rest of the procedure. This ensures that the tripod is
level.
B.
First
make sure the 5 inch telescope is in focus by focusing it on the Moon, if
visible, or on a distant building. Unlock
the Dec and set the Dec pointer to 90 degrees on the Dec setting circle. Lock
the Dec. Following
this, the axis of the telescope should be parallel to the polar axis of the
mount.
Note: The Dec setting circle has two scales: zero to +90 degrees for the
north celestial sphere and zero to -90 degrees for the south celestial sphere.
Although neither sign appears on the Dec setting circle, it is easy to remember
which scale is for positive Dec angles: it is the scale that points in the
direction of Polaris.
Set the altitude scale to 30.5 degrees, the latitude of
Tallahassee. Set the R.A. so that the
eyepiece is in a comfortable position for you. Using only the azimuth and altitude controls, aim the telescope towards
Polaris, first by sighting along the barrel, then using the finder scope and
finally using the 5 inch telescope. When finished, make certain that Polaris is
near the center of the field of view. (Note the altitude has a coarse and fine
adjustment, while the azimuth has only one (coarse) adjustment.) Now the polar axis of the mount should be
parallel to the axis of the Earth.
C.
If
your telescope is properly adjusted Polaris ought to be near the center of the
telescope with a weak star above, a bright star to the left and a weak star at
the bottom. (Note: Since Polaris is actually about 3/4 degree from the North
Celestial Pole this procedure aligns the telescope to approximately one degree
accuracy.)
II.
FINDING
THE GUIDE STAR – SAY ALTAIR
A.
From
now on don’t move the tripod! Make sure the motor is disengaged and power the motor using the battery
pack. Unlock the Dec and set it
to the Dec for Altair (+08 degrees, 52 minutes and 37 seconds, see p. 104, Lab
Manual). Lock the Dec. In principle, if your
Polaris alignment was done accurately, the Dec will now be correct for the guide star
(in this case Altair) and you need only move the telescope in R.A. to find the
guide star. Unlock the R.A.
and move the telescope in R.A. until Altair comes into the field of view of the
telescope. If the guide star does not come into the field of view then either the
Dec, the polar alignment or both are incorrect. If so, go back and repeat the procedure in Section I.
Moderately tighten the R.A. lock so that the R.A. fine
adjustment can still be used to adjust the
telescope to position Altair exactly at the center of the field of view. Now
engage the motor drive so that the telescope tracks Altair. You should check that the motor
gear is engaged (the large gear wheel should mesh with the small one.) Now tighten the R.A. lock. If you have followed this procedure, Altair should remain
centered in the field of view.
B.
Loosen
the R.A. setting circle screw (see Fig.
1), being careful not to loosen the screw
so much that it falls out. The
R.A. setting circle now turns freely and should be set to the R.A. of Altair
(19 hours, 50 minutes and 47 seconds, see page 104, Lab Manual). The R.A. setting circle is now aligned with
the R.A. lines in the sky. Tighten again the R.A. setting circle screw. The R.A. setting circle
will now follow the celestial sphere and remain
aligned with the R.A. lines in the sky.
III.
MOVING
TO LOCATIONS OF OTHER CATALOGED CELESTIAL OBJECTS
Look
up the coordinates of the celestial
object of interest. Loosen the lock for the Dec and set
its value, on the Dec setting circle, to that of the object of interest; then tighten the
lock again. To set the R.A., disengage the motor, loosen the
R.A. setting circle screw first, then unlock
the R.A. and move the telescope until the R.A. pointer points to the new
R.A. value.
Don’t move the R.A. setting circle,
otherwise you will ruin its alignment with the R.A. lines in the sky!
Lock the R.A. again and tighten also the R.A. setting circle screw so
that the setting circle will continue to track the celestial sphere when the
motor is re-engaged. If your alignment and settings are correct
the new object will be in the field of view.
You may need to make some fine adjustments using the Dec and R.A. fine adjustment knobs to center the object.
Finally, re-engage the drive motor.