Jump to content


Photo

Which stars are best for polar alignment?

  • Please log in to reply
6 replies to this topic

#1 dragon86

dragon86

    Explorer 1

  • -----
  • Posts: 75
  • Joined: 25 Oct 2010
  • Loc: Erie, Pa.

Posted 16 July 2013 - 07:39 AM

When aligning using a wedge are there specific areas of the sky to use? I have just started using a program called alt/az align to setup my scope and have been having good go-to's. Moved my mount and needed to re-polar align. Should I use East/West stars for EQ align then a southern star for polar align? Does it matter? Should the polar alignment star I use be above or below the celestial equator?

#2 cn register 5

cn register 5

    Viking 1

  • -----
  • Posts: 760
  • Joined: 26 Dec 2012

Posted 16 July 2013 - 10:51 AM

Avoid Polaris and the area round it.
The Zenith is OK but difficult to use with a finder.
I would use one star to the SW and one to the SE and not too high. Arcturus and Altair at present for me.

#3 btieman

btieman

    Viking 1

  • -----
  • Posts: 891
  • Joined: 24 Jul 2008

Posted 21 July 2013 - 08:51 AM

When aligning using a wedge are there specific areas of the sky to use? I have just started using a program called alt/az align to setup my scope and have been having good go-to's. Moved my mount and needed to re-polar align. Should I use East/West stars for EQ align then a southern star for polar align? Does it matter? Should the polar alignment star I use be above or below the celestial equator?


Don, I use any stars that are convenient for the initial alignment. It's generally considered best to use stars that are fairly far apart though crossing quadrants of the sky is not necessary. The scope has a model of the sky, aligning to stars is just telling the scope how the model is oriented.

For all-star polar alignment, I pick stars as straight south as I can. This makes the mental model of which direction alt/az adjustments move the target star much simpler since it's straight up/down and right/left. I usually pick a star near the celestial equator.

Since you're concerned about polar alignment, I assume you'll be imaging. For best alignment, align all stars with your camera. It's quite easy to align to a few arc seconds with a camera--much better than what's doable with your eyes. I've gotten 60 minute narrowband images with nice round stars using all-star polar align like this...no drift alignment!

#4 rmollise

rmollise

    Hubble

  • *****
  • Posts: 15797
  • Joined: 06 Jul 2007

Posted 21 July 2013 - 11:37 AM

When aligning using a wedge are there specific areas of the sky to use? I have just started using a program called alt/az align to setup my scope and have been having good go-to's. Moved my mount and needed to re-polar align. Should I use East/West stars for EQ align then a southern star for polar align? Does it matter? Should the polar alignment star I use be above or below the celestial equator?


It's not clear to me what you are asking. Are you asking about stars to use while performing a drift polar alignment, or go-to alignment stars?

#5 dragon86

dragon86

    Explorer 1

  • -----
  • Posts: 75
  • Joined: 25 Oct 2010
  • Loc: Erie, Pa.

Posted 21 July 2013 - 02:42 PM

I am using the stars suggested(and have tried my own selections)by the program called ALT/AZ ALIGN for my initial EQ north alignment. It seems that I cannot get below 3 minutes in AZ no matter what I try although I can get 0.2 in ALT. (When I check my numbers after doing a polar align then another EQ align.) I have no western view to do a drift align. If there is a problem with the equipment I have found most times the fault is with the operator!
Since I have tried so often to get this right it must be my procedure that is wrong. I do use the Mallincam for aligning.

#6 A. Viegas

A. Viegas

    Apollo

  • *****
  • Posts: 1094
  • Joined: 05 Mar 2012
  • Loc: New York City/ CT

Posted 21 July 2013 - 08:31 PM

Don,

For what its worth, pick a star as close to 0 dec and just west of the meridian. Depending on the day and time of the week, there are a few of the main stars in Ophiuchus that fit the bill at this time of the year. This friday evening i used Kappa Ophiuchi "SAO 121962" and i was able to get polar alignment very precise on my HD Wedge CPC1100...

Al

#7 Cellofan

Cellofan

    Sputnik

  • -----
  • Posts: 39
  • Joined: 21 Jun 2007
  • Loc: Venice - Italy

Posted 30 July 2013 - 07:58 AM

With the CPC-1100 in equatorial for photographic, I use Castor and Alpheratz almost time of day, how can I? With Astroplanner or BestPair: Let us assume that it is 10.00 pm I check with one of the two programs mentioned in that I now have the best alignment. Let us assume that one of the two programs I signals at 9.00 am the best alignment. I select from Nexstar, the time required for the best alignment (time and date) on the keyboard of Nexstar provided by one of the two programs, I select "Eq North Align", meanwhile the telescope is oriented manually SOUTH 45 ° altitude (DEC +00 00 00), Nexstar responds "Set Alt to Index", I press ok, the request "Find Meridian," I press ok, the telescope slews to the first star, "center ok" and "ok align", the telescope moves on the second star, "ok center", "align ok." At this point, the precision of the goto is what it is. At this point I give the keyboard NexStar the exact time at which I find myself. Nexstar updated to the current time, start AstroTortilla to calibrate the goto precisely around 3 to 6 arcsec.
Easy, easy, alignment favorite stars at your best every time.
P.S. select a target on meridian near the equator BEFORE STARTING AstroTortilla.






Cloudy Nights LLC
Cloudy Nights Sponsor: Astronomics