Telescope Reviews: AS CG5 GT New Software Alignment/Calibration Stars

Patrick:

Please be advised that I read somewhere in Celestron's literature that Celestron does, in fact, recommend for their 2 Star Alignment Procedure: 2 Alignment Stars and 4 subsequent Calibration Stars. If I remember correctly I think that this procedure was specific to the AS CG5 GT Mount. I will check on that issue and get back with you on it since I know that you use that mount as I do.

Here is a summary of what Don advised me when he responded to my rather poorly phrased questions on this issue which I have put in a Q and A format:

Question: From looking at Celestron's literature, it seems that the intial 2 alignment stars are all on one side of the meridian and that they should be as widely spread apart as possible. The question is which stars should one use on the East and which on the West for the initial 2 star alignment? I would assume that one would select the ones that the computer picks, but that may not be the case; and, it well may depend upon what calibration stars are selected as well as where the initial stars are located in the sky, i.e. lower half of the sky dome or upper half of the sky dome.

Answer: "Accuracy is highest, from what little knowledge of cartography I possess, when one star is south of the equator, one star is north (both east), and one star is near the equator (in the west), though as long as the triangle is large, calculations should pick up cone error. Do not use any star near the pole as smaller and smaller movements of the mount result in larger and larger errors."

Question: As for the 4 subsequent calibration stars, the same question applies --which ones and where should they be located on the opposite side of the meridian for the creation of the sky model for purposes of the best alignment?

Answer: "Using alignment stars near the field of primary target results in the greatest accuracy, which is the raison d'être of Precise GoTo."

Question: "This is relevant because in trying to understand how the computer program algorithms work it may be that the alignment stars and calibration stars selected in the intital 2 star alignment (and subsequent 4 calibration stars) need to be selected in the bottom half of the sky's half dome (i.e. in the area from the horizon to say 45 degrees up from the horizon) or would they need to be selected in the upper half of the sky's half dome (i.e. say 45 degrees up to the zenith).

Answer: "Stars near the horizon suffer from refraction and choosing them will cause errors. Never chhose an alignment star closer to the horizon than 30 degrees."

Question: If the computer is creating a model of the sky I think that this may be important to know because a more accurate model would obviously be created depending upon how the program's algorithms work. This is important because if the next step is to do the computer's polar alignment [which is based upon the initial 2 star alignment (and 4 calibration stars)]; then after the polar alignment, a second 2 star alignment is required (with another 4 calibration stars).
> The issue for purposes of the creation of an extremely accurate sky model in the computer becomes which stars are now to be chosen in the second 2 star alignment (and 4 calibration stars)?

Answer: "They can be the same stars. The accuracy will depend on accurate centering of the stars. You don't need to worry about the speed with which you choose the stars, either, as the clock is running while you select. Your confirmation of the location of the second star confirms the "twist" of the celestial globe relative to the first star."

Question: If, in the initial alignment the stars in the lower half of the sky's half dome are selected (i.e. stars from the horizon level to say 45 degrees up); then in the second 2 star alignment procedure, should stars in the upper half of the sky's half dome be selected (i.e. stars from 45 degrees to the zenith)?
> The central question is which stars of the 12 stars which are used in the alignment process (i.e. the 4 alignment stars and 8 calibration stars utilized in 2 separate alignment procedures) should be used; and, in what sequence should they be chosen, in order to create the best model of the sky for the Celestron 4.15 and 4.16 software program to create the most effective model of the sky.

Answer: "I'm not sure it's real critical because I've used the 3 stars chosen by the mount, I've chosen them myself, I've had them close together, and far apart, and the pointing accuracy has been good in every case."

Question: I am sure that somebody knows the answer to this question, but I don't know who. I checked Mike Swanson's website and could not find the answer there. I googled it without success so far. I've posted the question on CN and the last time I looked I there was no response which answered the question. Celestron's software engineers should know or at least the person who wrote the program should know. If all else fails, I plan on writing to Celestron to try to ascertain this information.

Answer: "The program was written by Synta Corporation, so I hope you speak Chinese."

Question: On Mike Swanson's website there is a computer program called "Best Pairs" which was written for the Meade LX 200 fork mount which selects the best pairing of stars for the Meade autostar program. Something similar must exist for Celestron.
> Moreover, since other computer programs interface with Celestron's 4.15 software [such as Starry Night Pro and The Sky] there must be something out there which identifies which 12 stars and in what sequence best align the telescope's mount.

Answer: "The accuracy should be highest with the greatest separation so long as no star is below 30 degrees (meaning alignment stars could be as much as 120 degrees apart)."

I like Don's reasons as they make sense to me. When I have some time this coming week I would like to create an "alignment map" of the night sky to be used in the early evening (dusk and thereafter) to use to model the sky according to the parameters that Don has set forth plotting out the 4 Alignment Stars and the 8 subsequent calibration stars.

Maybe someone who has more free time available and a similar interest may beat me to the punch on this; and, if so, I would be interested as there is no need to re-invent the wheel. On the other hand, others may well have thought this matter through along a similar path and have some input to offer as well. It certainly would be welcomed.

Finally, as previously stated I am really interested in learning how to fully use this new software, including all of its functions such as "Solar Align;" "Polar Align;" "Precise GoTo;" "Synch Function;" the "Hibernate Function;" and, the other functions.
Best regards,
William