I believe stars do not move exactly at Sidereal rate if they are not near the Meridian.

Correct! The *apparent* movement rate of stars is slower than sidereal because of refraction.

If you were looking at the star at certain distance from the Meridian, then that might explain what I just said.
Which is why we have software to create pointing model of the sky to take into account of everything including
refraction in the sky. I don't think you can successfully take unguided long exposure images without pointing
model even with perfect polar alignment.

This is mostly true. One may get lucky in certain parts of the sky where telescope flexure, mis-polar alignment, and
refraction happen to balance themselves out, but this is usually rare. Modeling software can eliminate virtually all of
the tracking error.

-Ray Gralak
Author of Astro-Physics Command Center (APCC)
Author of PEMPro: http://www.ccdware.com
Author of Astro-Physics V2 ASCOM Driver: http://www.gralak.com/apdriver
Author of PulseGuide: http://www.pulseguide.com
Author of Sigma: http://www.gralak.com/sigma

-----Original Message-----
From: ap-gto@yahoogroups.com [mailto:ap-gto@yahoogroups.com] On Behalf Of topboxman2000
Sent: Saturday, July 27, 2013 7:03 PM
To: ap-gto@yahoogroups.com
Subject: [ap-gto] Re: RA Drift





Correct me if I'm wrong. I believe stars do not move exactly at Sideral rate if they are not near the Meridian. So
if you center the star 2 or 3 hours away from the Meridian and came back in 30 minutes and the star will likely
move (very slightly) from original location in RA axis direction.

If you were looking at the star at certain distance from the Meridian, then that might explain what I just said.
Which is why we have software to create pointing model of the sky to take into account of everything including
refraction in the sky. I don't think you can successfully take unguided long exposure images without pointing
model even with perfect polar alignment.

Peter

--- In ap-gto@yahoogroups.com <mailto:ap-gto%40yahoogroups.com> , "rickysguy" <jmartin590@...> wrote:

Hi all,

Getting my new Mach1 set up, I drift aligned until I got no north south movement after 5 min using my CCD

camera and a cross-hair overlay on the two stars I used. However, I did notice a tad (one star diameter)
movement in a westerly direction. I thought that this might be due to my mount tracking a bit slow. I guess
guiding would correct this, if it is due to slow tracking but, I had hoped to get 5 minutes unguided out of the
mount. Is this expectation unreasonable? I see that there is an input in the AP driver to "customize" tracking
like for comets but, I don't know if I should use this option or, if I did, how much to increase the tracking rate
from sidereal.

Another question has to do with PulseGuide program. I tried to connect it to the mount but, since I am using

the AP driver to connect through Stellarium Scope and Stellarium, Pulse Guide will not connect. Is there a way
to use both programs at the same time or, do I have to connect another serial/usb adapter to the second serial
input on the CP3?

Thanks for any answers.

Jon