Editing Glossary (section)

===== Field rotation =====
----Field rotation is an imaging problem most commonly found in alt-azimuth mounts and essentially makes them impossible to use for long exposure astrophotography. If you open up a planetarium program such as Stellarium and turn the speed up you'll notice that as the targets move across the sky they appear to 'rotate' in relation to your position on earth - for example a constellation rising in the east will be upside-down by the time it sets in the west. Equatorial mounts counter this due to their tracking method following the earth's rotation, alt-azimuth mounts can't as they aren't polar aligned and are tracking on two axes. This causes the stars in your image to rotate around the center of the frame.