Re: [APML] Wide-field on polar mount + astrophotography inSyria

[Gene Horr <genehorr@texas.net>]

Jim Ives wrote:

>     You mention the "king" tracking rate. I have that on my MI-250 mount and
> have never used it. What is it? And is there a real use for it??

Due to 
atmospheric refraction an object only moves at the sidereal rate
directly overhead.  Away from the meridian it moves at a different
rate (slower? faster?  I don't remember).  The King rate compensates
for this.  I don't remember at which hour angle you should stop
using sidereal and start using King.  And IIRC the object's altitude
also plays a part.

Now, to confuse things, personally I do not use the King rate.....  I
haven't noticed any harm in this.

Gene Horr
genehorr@texas.net

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