Autoguider

An autoguider is an automatic electronic guidance tool used in astronomy to keep a telescope pointed precisely at an object being observed.

This prevents the object from drifting across the field of view during long-exposures which would create a blurred or elongated image.

In order for the resulting image to maintain usable clarity and sharpness during these exposures, the target must be held at the same position within the telescope's field of view during the whole exposure; any apparent motion would cause point sources of light (such as stars) to appear as streaks, or the object being photographed to appear blurry.

The device has a CCD or CMOS sensor that regularly takes short exposures of an area of sky near the object.

To prevent the telescope from moving in response to changes in the guide star's apparent position caused by seeing, the user can usually adjust a setting called "aggressiveness".