Jump to content


Photo

Polar alignment

  • Please log in to reply
10 replies to this topic

#1 wargrafix

wargrafix

    Messenger

  • -----
  • Posts: 439
  • Joined: 10 Apr 2013
  • Loc: Trinidad

Posted 07 October 2013 - 06:06 AM

Hi everyone, if you can't see polaris, but need to polar align, dropping the compass and compensating for declination, say, negative 14 degrees will do the job?

#2 AlBoning

AlBoning

    Viking 1

  • -----
  • Posts: 592
  • Joined: 06 Mar 2011

Posted 07 October 2013 - 06:23 AM

Setting up before sunset for a star party the use of a level and a compass has gotten me close enough on occasion that a GoTo, starting from home position without a x-star alignment (of course, the Sun is up) has put the Moon or Jupiter into the the field of a low power eyepiece.

As the saying goes ... Good enough for visual work.

#3 wargrafix

wargrafix

    Messenger

  • -----
  • Posts: 439
  • Joined: 10 Apr 2013
  • Loc: Trinidad

Posted 07 October 2013 - 07:08 AM

Thank you very much. the mount is level, but I was wondering, do you compensate for declination?

#4 rmollise

rmollise

    Hubble

  • *****
  • Posts: 15567
  • Joined: 06 Jul 2007

Posted 07 October 2013 - 09:58 AM

Leveling won't help. Using a compass and taking magnetic variation into account will indeed do the job for visual observing. If you plan to take pictures, or your mount is picky about polar alignment vis-à-vis go-to, you will need to use another method, like drift alignment.

#5 end

end

    Ranger 4

  • -----
  • Posts: 357
  • Joined: 31 Aug 2011
  • Loc: Houston, Texas, USA

Posted 07 October 2013 - 11:07 AM

The following was adapted and updated from a post that I read here several months ago by WadeH237. It allows for pretty good day time polar alignment and (obviously) does not require the ability to see Polaris. I now use this whenever I go to a remote site and am setup before sunset. It assumes a Celestron mount, but could easily be adapted for other mount varieties.


1. Power on the mount as normal: either align the index marks (CGEM or CG-5), or let the homing switches do their thing (CGE-PRO). Enter time and site information as required.

2. Select “Quick Alignment”.

3. Turn off tracking.

4. Register the OTA’s RA to the Mount’s RA: In the Utilities menu, find “Goto Axis Position”. Enter azimuth 180° 00’ 00”, altitude 90° + local latitude to put the mount with the scope on the west side with the OTA pointed north. Release the RA clutch and use a bubble level to make the counterweight shaft perfectly horizontal. Re-tighten the RA clutch.

5. Register the OTA’s declination to the Mount’s declination: Again, find “Goto Axis Position”. Enter 90° 00’ 00” for azimuth and 180° 00’ 00” for altitude and press enter. The mount should slew such that the OTA is pointing to the western horizon and is level. While in this position, loosen the declination clutch and use a bubble level to make the OTA perfectly horizontal. Re-tighten the declination clutch.

Steps 4 & 5 basically accounted for the fact that your tripod or pier is probably not perfectly level.

6. Correct Mount & OTA’s polar alignment in Altitude: Go back to “Goto Axis Position” again. This time, go to 180° 00’ 00” for the azimuth and enter 90° + local latitude for latitude. Hit enter. This time, the mount will slew so that the OTA is on the west side of the mount and level pointed north. Use a bubble level again to ensure that the OTA is perfectly horizontal. This time, though, do not release any clutches and do not hit any buttons. Use the mount's altitude adjustment knob only to level the OTA.

7. Turn on tracking.

8. Correct Mount & OTA’s polar alignment in Azimuth: Use goto to pick any object that you can see during the day, like the Moon, the Sun or Venus. When the mount is done slewing, use the mount's azimuth adjustment knobs to center the object. Do not release any clutches and do not hit any buttons on the hand controller.

The mount is now polar aligned in both altitude and azimuth. In my experience this process will result in a polar alignment error of less than 1 degree in both axes. When it gets dark enough, you can now power cycle the mount, do your normal 2+4 alignment routine and start using the mount. If necessary / desired a subsequent ASPA (Celestron’s All Star Polar Alignment) or drift alignment can be performed.

#6 wargrafix

wargrafix

    Messenger

  • -----
  • Posts: 439
  • Joined: 10 Apr 2013
  • Loc: Trinidad

Posted 07 October 2013 - 02:06 PM

Thank you everyone. I really want to see if I can do this right. I think the alt-Az knobs is the crucial point I missed. I have a funny problem where the only star the goto keypad are west of my lawn, and the house blocks the western sky. darn it!

#7 wargrafix

wargrafix

    Messenger

  • -----
  • Posts: 439
  • Joined: 10 Apr 2013
  • Loc: Trinidad

Posted 10 October 2013 - 09:00 AM

Ok, I gave it a try, leveled tripod and head, sighted Polaris and then power went.It was nice to have dark skies but of course i could do alignment. When the power came back i tried to do the alignment but all the stars that available are to the west and my hose blocks them. is there a way to force the system to choose stars to the east? I am losing patience with this. :-(

#8 dmdouglass

dmdouglass

    Viking 1

  • -----
  • Posts: 750
  • Joined: 23 Dec 2007
  • Loc: Tempe, AZ

Posted 10 October 2013 - 09:41 AM

Wargrafix...

Your description says that you are probably using a Celestron product. The "fix" is easy...

When the "star" is displayed, it should also be showing a "W" on the screen. Press the "Menu" button, and the "W" will change to a "E", and away you go...

The routine, by default, uses two "W" stars, and then offers calibration stars in the "E". When you press the "Menu" button, it reverses.

#9 wargrafix

wargrafix

    Messenger

  • -----
  • Posts: 439
  • Joined: 10 Apr 2013
  • Loc: Trinidad

Posted 10 October 2013 - 10:19 AM

ohhhhhhh. goodness I feel like a noob. Thank you kindly. The goto is giving me hell, I really really hope i can get it to work. Question though, for a slight incline, how is the safes way to to level the mount?
I have some moon photos to upload and I feel I should be contributing to the forum since everyone helps so much.

#10 dmcnally

dmcnally

    Mariner 2

  • *****
  • Posts: 230
  • Joined: 16 Mar 2012
  • Loc: Lompoc, CA

Posted 11 October 2013 - 06:52 PM

Wargrafix...

Your description says that you are probably using a Celestron product. The "fix" is easy...

When the "star" is displayed, it should also be showing a "W" on the screen. Press the "Menu" button, and the "W" will change to a "E", and away you go...

The routine, by default, uses two "W" stars, and then offers calibration stars in the "E". When you press the "Menu" button, it reverses.


I thought I'd RTFM for my CGEM pretty thoroughly and I missed that one. I checked the manual and I did find it. It's on the right side of page 19 in a side note of the 2008 version of the CGEM 800/926/1100 manual.

Thanks again,
Dave

#11 wargrafix

wargrafix

    Messenger

  • -----
  • Posts: 439
  • Joined: 10 Apr 2013
  • Loc: Trinidad

Posted 14 October 2013 - 08:07 AM

ahhh. Its not present in the GT manual. Not sure where it is...






Cloudy Nights LLC
Cloudy Nights Sponsor: Astronomics