Last updated: 24 February 2001

Polar Alignment Tips

From: jim@emmgraphics.com (Jim Berry)

Am I the only person using the Autostar in polar mode? Frankly, I think it works better that way - I believe tracking is much smoother, possibly because it only has to use one motor, and tracking also involves a lot less calculation (really now, the Autostar can't even calculate the planets' positions properly - I want it to do as little thinking as it has to.) Anyway, I thought I'd pass on the process that I use to do alignment - there's a tip in there that might be helpful for Alt/Az folks, too...

First, the scope must be pointed at 90 degrees North relative to the base. Folks have recommended levelling the base with a bubble level, and then using the level to set the optical tube vertical. I used to do that, but it never really worked very well. Here's what I do now:

Put a low-power eyepiece into the scope and focus it. Now put the scope into the 90 degree North position using the setting circles or a level, or however you want to do it (it only needs to be close.) Make sure the RA axis is free to rotate, and **by moving the telescope base** point the scope into a reasonably star-rich area of the sky. Look through the scope while you rotate the RA axis. If everything were exactly perfect, you would see all of the stars moving in circular arcs around the center of the field. If there were a star in the center, it would be sitting still.

In real life, however, you will probably see stars moving in really wide arcs across the field. Rotate the scope (either use the paddle or unlock the dec axis and do it manually) towards the "inside" of these arcs a little and check again. At some point you will get to where the stars are moving in circles. Move the center of these circles as close as possible to the center of your field-of-view (it's interesting to note that, as likely as not, the center will be positioned either left or right of center, indicating a slight east/west misalignment of your optical tube in the mount, which can be corrected, but I won't go into it here.) Now your scope is _really_ pointed along the RA axis.

For people doing Alt/Az alignments, this last bit makes a useful sanity check. If you level your tube using whatever method you use, and then rotate it 90 degrees to point straight up along the azimuth axis, you should be able to see the center of the "circles."

The rest of the polar alignment process is straight out of the manual. Without unlocking the dec axis or moving the scope in declination, position the base so the scope points to Polaris (sorry Southern hemisphere folks - you're on your own.) Now, while watching Polaris, move the base so the telescope's aim point moves in the direction of Kochab (the bright star at the other end of the Little Dipper from Polaris.) If Kochab isn't visible, move _away_ from the "wide" end of Cassiopeia's "W". Ideally you'd like to move Polaris about 45 minutes of arc (3/4 of a degree.) With my ETX-90 and the 26mm eyepiece, this is done by moving Polaris just out of the filed of view. At this point, the scope is pointed within a few minutes of arc or so from the pole, and the mount is pretty accurately polar aligned.

I'm a "control panel goes on the West side" person. If you're not, some of the rest of this might not be right, but... Now rotate the RA axis counter-clockwise (from above) until it hits the hard stop. Then rotate clockwise until the eyepiece is pointed "up" as well as you can eyeball it. Accuracy in this process will affect how well the Autostar initially points towards alignment stars in RA, but isn't crucial in the long run.

Now lock the RA axis and do the Autostar alignment. I always do a 2-star alignment, since "Easy" invariably picks stars that I can't see and tries to point to Polaris, which is an insanely stupid thing to do, since 50% of the time it'll have to point the eyepiece straight down in order to do it (actually, I might be wrong: does "Easy" still try to point to Polaris?) Anyway, just use "2-star" and choose your own stars - it's good for you to know them anyway. :-)

After you choose each alignment star, the telescope will slew to it. Ignore any error in RA, since it's just a question of the initial RA ("eyepiece up") position not being exactly right, and the Autostar will take care of it. Declination errors, however, indicate a mount alignment problem. If it's within a few degrees everything'll be fine, but if it's really bad then you've probably done something wrong. At this point if the initial slew's declination is bad I usually start all over again. You do get better with practice, though, and it's been a while since I had to align more than once.

Anyway, it works for me. Good luck.


-jim berry
ETX/QuickCam images at: www.emmgraphics.com/pilot

Subject:	 Polar Alignment Tips for No-Fail Set-up
Sent:	Wednesday, January 17, 2001 05:51:14
From:	sherrodc@ipa.net (Clay Sherrod)
This is in response to a recent post here on the site and may be value
to others:

Glad you got the new ETX 125; after a little frustrating "tweaking" and
learning all the fine tuning aspects (you'll find that Mike's site is
your encyclopedia to the ETX world and beyond) you will be VERY please
with the performance and ease of use.

A word about your alignment problems. I prefer to use my ETX 125 in
POLAR mode as you are attempting, since tracking and GO TO seems better
for me; a lot of people, as Mike points out, prefer the Alt-Az.  If you
are using the #883 tripod, by all means use the Alt-AZ configuration! 
The scope is too heavy in Polar offset for the #883!

Anyway, let me address a couple of things you must carefully check in

1)  As Mike mentioned, it is VERY important to get in under
"Setup/Telescope/Mount...." and click POLAR, then "Enter" to operate in
Polar Mode;

2) However, from your description of "pointing at the ground" in home
position, I know what your problem is.  It is VERY difficult to get into
home position in POLAR position unless you remember a VERY important
rule:  Watch out for the "stops."  In Polar position, aim your scope at
90 degrees, or at Polaris; in this position, your scope optical tube
assembly will be IN LINE WITH the extended fork arms, aiming due north
and elevated to your latitude.  MAKE SURE THAT THE "BUTTONS", the little
knobs that screw into the table-top holes (or the table top tripod front
legs, if that is what you are using) are both facing northward, or
aligned above the northern tripod leg.  THIS WILL PUT THE CONTROL PANEL
on the WEST side of your mounting - very, very important!!

Likely, in this position, your EYEPIECE WILL BE POINTING DOWN.  Now, do
the following:

hit one of the internal stops.  DO NOTHING until you do this first.

4)  Now, all you have to do is rotate the scope CLOCKWISE, away from the
stop until the EYEPIECE is aimed straight up; in this position the
UNMARKED "setting" circle (the declination clamp arm) of the fork will
be OVER THE CONTROL PANEL (the control is on the WEST side of the

5)  You are now in Polar Home Postion!

Try it and let me know; it is a good idea to do this every time (turn
counter-cl. until hitting the stop and then rotating clockwise until
eyepiece is "up"), because with all the motion the telescope undertakes
the rotation might not be the same as it was when you finished the last

I think this will help you....it is a very easy and confusing setup to
make until you get used to it!

With best regards
Clay Sherrod,   Conway, Arkansas

Subject:	Polar alignment
Sent:	Thursday, February 22, 2001 05:55:15
From:	niko.deleu@ictportal.com (Niko Deleu)
I would like to explain my way of polar alignment.

1) Use a bubble level to level the tripot.
2) Turn the scope counterclockwise until the hard stop.
3) Turn the scop clockwise +/- 180 degrees util the finder is pointing up.
4) Use a bubble level to make sure that the end of the forks are in
PERFECT "GO TO" ETX OR LX 90 - Part 3 (Fig 3.E) on this website.
5) Tighten the RA lock.
6) Loosen the decl knob and place the tube horizontal using a bubble level.
7) Tigthen the DECL lock.
8) Turn off the scope.
9) Turn back on the scope.
10) Hit the mode button for two seconds so you can see the DECL/RA
coordinates. The scope thinks it is 89.59 decl.  In fact it the tube if
now perfectly horzontal. If you live for instance at 50 degrees north,
hit the up-arrow until your declination settings read 40 degrees. (90 -
your lattitude)
11) You are now sure that declination of the scope is perfectly 90
degrees ! This is much more accurate than using your decliation scale
which is difficult to use accurately in complete darkness.
12) Turn back off the scope.
13) Turn back on the scope.
14) Hit the mode button for two seconds, the scope thinks again that the
declination is 89.59 degrees, and this is CORRECT.
15) Using the tripod or wedge adjustments only, you want to RAISE the
telescope assembly in the eyepiece FOV until Polaris is at the very EDGE
of a one-degree FOV eyepiece; now the object is to move the telescope
assembly until it is offset that exact ONE DEGREE from Polaris toward
Kochab. To do this, merely slowly tweak the slow motion controls of the
tripod or wedge until Polaris reaches the OPPOSITE EDGE of the FOV, in a
direct line toward Kochab. Once on this edge, the telescope is offset
about one degree from Polaris and very close to the true celestial pole.
ETX OR LX 90 - Part 3 ) 16) Now you have a perfect polar home position
to do a polar alignment with your autostar.

Niko Deleu

ICT portal 
Niko Deleu

Return to the top of this page.

Go back to the Autostar Information page.

Go back to the ETX Home Page.

Copyright ©1999-2001 Michael L. Weasner / etx@me.com
Submittals Copyright © 2000-1 by the Submitter
URL = http://www.weasner.com/etx/autostar/as_align3.html