Quote:
Originally Posted by Astro_Bot
Having a quick look at the maths above, for RA, you could just add 12 hours and check the resulting hour component (if >=24, subtract 24). It would save a lot of conversion.
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Thanks Astro_Bot. Since the RA values will always be positive, adding the 12
and keeping in the range within 0 to 24 will do the trick.
Lars, you have to however take care with the Dec calculations, particularly
when negative values are involved. It is important to remember that if you
have a Dec such as -57:02:32.1 it is really -57 degrees, -2 minutes, -32.1 seconds.
Particularly be mindful of the case where the degree field is negative 0.
For example, -0:12:34. You need to apply the sign to all fields. Your Scope Dec
values will end up being in the range -180 degrees to +180 degrees.
Your star Dec values however will only ever be in the range -90 degrees to +90 degrees.
In other words, don't touch the star RA and Dec fields, only the scope RA and Dec fields.
By the way, when I mentioned that NP was virtually non-discernible, I was
looking at its value compared to its own standard deviation (reported as sigma).
The standard deviation was close to the size of the term's value, so it really
was down in the noise on the limited number of points fitted.
Physically, Dec to optical axes non-perpendicularity was the dominant term,
which is common on GEM's. As I mentioned, if the OTA is not "square" to
a dovetail plate or the plate not "square" to a mount head, CH will come about.
There are a variety of other potential reasons, including the optical path
not being parallel to the tube (collimation) or a camera coupling that is skewed.
When you perform the spreadsheet conversion, you might like to post
an updated .dat file and we can have another quick look.
But I am hoping it will be all over bar the shouting.
