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If I take a shot longer than 20 seconds, the stars get a tail. I have a Celestron Advanced GT mount with starshoot autoguide scope. I use a cannon can on a 9" Celestron scope. I can't get a picture without having tails on my stars. It only looks good if I keep the pictures under 20 seconds.

EDIT :

I did the polar alignment. The mount has a polar alignment scope threw the center of it. It's also balanced, the mount has a brids eye level. I use the new PhD software with the starshoot autoguide.. There is no slop in the mount, the gears have almost no backlash.

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If you can't get any longer than 20 seconds, chances are it's your polar alignment. The mount you have is a motorised GoTo EQ mount (I believe), but if these aren't aligned properly, then they can still have trouble.

Also, depending on your software, try a 2 or 3 star align to get a better accuracy.

Also check the scope is nicely balanced with the camera on the end, and that your mount can take the weight.

EDIT :

If you try all this and you are still getting trailing, it may be worth going to a professional to get the mount looked at. It may be faulty.

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you need a motorized equatorial mount, which tracks the stars in such a manner as to cancel the rotation of the earth and eliminate the tails on your photos. These are commercially available for many common types of telescope mounts.

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  • $\begingroup$ It would be nice to have more information. Have you done polar alignment? Have you balanced your system as best as possible? Are you using some software such as PhD for autoguiding? $\endgroup$ – astromath Mar 26 '18 at 7:28
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    $\begingroup$ The Celestron Advanced GT mount is a motorized equatorial mount, so that's not the problem. $\endgroup$ – Dr Chuck Mar 26 '18 at 8:22

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