Re: Question from a prospective buyer: All Star Polar Alignment


hubbell_jerry@...
 

Hi Joe,

I completely understand your point of view. Most beginners want the equipment to be easy and want to get to the observing part without having to mess with the setup of the equipment. Anything that make the setup easier is most welcome. I understand that beginner mounts from other companies may provide some automation to align the mount, but the G11 is not really considered a beginner mount and requires some knowledge before operating it effectively. There is a polar alignment scope available for purchase, but we don't include that because most of our G11 customers are not beginners and do not want to spend the extra money for a polar scope on the G11.

We have not really done the best job of explaining the power of the 2 and 3-star alignment routine in the ExploreStars application and how to get a basic polar alignment without the use of a polar scope for the G11. Again, very few beginners will buy the G11 as their first German Equatorial Mount. The EXOS 2 mount comes with a polar alignment scope so the user can do a halfway decent alignment. The G11 is a different story.

One of the secrets about the 2 and 3-star alignment routine that I have coded in the ExploreStars application is that it was designed for those who do not or cannot do a decent polar alignment, or even level their mounts very good. The alignment routine is designed to convert the mount's coordinate system to the celestial coordinate system so that the mount points correctly. 

What this means is that the mount could be up to 10-15 degrees off of north and the altitude could be a few degrees off and it won't matter. You could literally look at your horizon and say "that looks about north" and plop your mount down and not bother setting the altitude or level. We have demonstrated this at star parties we have attended in 2016 and since.

The trick though is that when you start the alignment, and the mount slews to the first star, you need to be able to identify that star correctly. Now if you are several degrees off, and you don't know how much exactly, you may pick the wrong star to SYNC on. This would through it off completely. This won't work of course. So even if the alignment routine can handle this much error, it still relies on the user to correctly identify and SYNC on the correct star as selected. This is a bit of a stretch for a beginner unless he is very familiar with the sky.

What we suggest is you use a compass and a level to do a daytime polar alignment that will get you to about 0.5 deg of the NCP if you are careful and practiced. 

The procedure is as follows:

1. Obtain the Longitude and Latitude of your location.
2. Using an online resource such as http://www.magnetic-declination.com/ and http://www.magnetic-declination.com/what-is-magnetic-declination.php to determine your Magnetic Declination.
3. Set up your tripod and level it as close as reasonably achievable.
4. Install your mount on the tripod with the counterweight bar over top of one of the tripod legs pointed north.
5. Using the Magnetic Declination determined in step 2, align your mount to True North by sighting
        at a distant object using the compass and aligning your mount with the object.
6 Install your telescope on the mount.
7. Connect up the PMC-Eight to the mount, power it up and get the ExploreStars working.
8. Once everything is working and ExploreStars is running, go to the coordinate input screen and enter the following coordinates into the RA/DEC:
DEC = your local Latitude Value
RA = your local LMST (as read off the display) - 1 minute
(this puts the telescope on the east side of the pier)
9. This will point the telescope near zenith. Place the level on the top of your telescope across the aperture being careful on to touch the optics.
10.  Adjust the north facing tripod leg to level the top of the telescope so that it is pointing at zenith.
11. Park the mount after getting level and you are ready to do a 2 or 3-star alignment as your mount should have a very good polar alignment at this point.

This is a bit different from using a polar scope, but it has an advantage in that you can do it during the day or night, and it does not require the north star to be seen in case it is blocked by trees.

I will work on creating a knowledge base article from this.

Although this is not quite as fancy as providing an electronic means to do a polar alignment, it does the job for visual observing. If you are doing astrophotography then there are several techniques available that are more precise than using this method or a polar scope that you would want to learn, I use the declination drift method which has the advantage of not having to see the north star also. Although a bit time consuming at first, it can be done in 5-10 minutes if you practice and are consistent when setting up your mount.

There are going to be a lot of things that you are going to want to learn to do where the equipment will not do it for you, especially if you are doing astrophotography. Learning the sky is one of them, as many beginners learn when they discover that you have to be able to identify the stars in the sky to do an alignment. Typically mounts do not align themselves as you know. Doing a polar alignment when you cannot see the north star is another skill that is very useful.

I will put a physical polar alignment function on the list of things to add to the ExploreStars application, but as I said, it will be a few months probably before I can even start to look at this.

Jerry Hubbell
Director Electrical Engineering
Explore Scientific, LLC. 


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