Astronomy Basics

6
move to the star near the eastern horizon. The star should be
20 degrees above the horizon and within five degrees of the
celestial equator.
• Ifthestardriftssouth,thepolaraxisistoolow.
• Ifthestardriftsnorth,thepolaraxisistoohigh.
Again, make the appropriate adjustments to the polar axis to
eliminate any drift. Unfortunately, the latter adjustments interact
with the prior adjustments ever so slightly. So, repeat the
process again to improve the accuracy checking both axes for
minimal drift. Once the drift has been eliminated, the telescope
is very accurately aligned. You can now do prime focus deep-
sky astrophotography for long periods.
NOTE: If the eastern horizon is blocked, you may choose
a star near the western horizon, but you must reverse
the polar high/low error directions. Also, if using this
method in the southern hemisphere, the direction of
drift is reversed for both R.A. and DEC.
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 co-ordinates line up with
the R.A. indicator (the zero mark on the vernier scale). The
R.A. setting circle should rotate freely. If the circle does not
move freely, loosen the thumbscrew to the right of the scale.
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 star chart to
make sure the object you chose is above the horizon. As
you become more familiar with the night sky, this will no
longer be necessary.
2. Look up the coordinates in a star atlas or reference book.
3. Hold the telescope and release the DEC clamp.
4. Move the telescope in declination until the indicator is
pointing at the correct declination coordinate.
5. Lock the declination clamp to prevent the telescope
from moving.
6. Hold the telescope and release the R.A. clamp.
7. Move the telescope in R.A. until the indicator points to the
correct coordinate.
8. Lock the R.A. clamp to prevent the telescope from slipping
in R.A. The telescope will track in R.A. as long as the motor
drive is operating.
9. Look through the finderscope to see if you have located the
object and center the object in the finder.
10. Look in the main optics and the object should be there.
For some of the fainter objects, you may not be able to see
them in the finder. When this happens, it is a good idea
to have a star chart of the area so that you can “star hop”
through the field to your target.
This process can be repeated for each object throughout any
given night.
aligning The r.a. seTTing CirCle
To increase the accuracy of the R.A. setting circle, the mount
comes with a vernier scale. This device allows you to get more
precise readings down to one minute of right ascension.
Before we go into the specifics on how to use the vernier, let’s
take a look at the scale and learn how to read it. First, the zero
(0) mark on the vernier is the R.A. indicator and will hereafter be
referred to as such. It is on the extreme right end of the vernier
scale with the other numbers increasing as you move toward
the left.
If the R.A. indicator is right on one of the marks of the R.A.
setting circle, then that is the coordinate the telescope is
pointing at. The problem arises when the R.A. indicator (zero
mark) is in between two of the marks on the R.A. setting circle.
If this is the case, you will notice that along the vernier scale,
one of the marks will line up with one of the marks on the
setting circle. This mark indicates the number of minutes that
should be added to the R.A. reading of the indicator. Since the
indicator is between two R.A. marks, add the minutes to the
lower value that the R.A. indicator falls between.
using The r.a. Vernier sCale