Astrophotography is a combination of art and science. Because the Earth is rotating during the exposure, the telescope must be slewing at the same rate, but in the opposite direction to keep the object being photographed in the center of the frame. This is done by a drive motor attached to the telescope's mount which must be exactly parrallel with the Earth's axis; a technique known as Polar Alignment. Still, fine adjustments must be made constantly by the astrophotographer to compensate for mechanical errors in the drive, changes in frequency of the line voltage to the drive motor, and image shifting caused by the shimmering effects of the atmosphere called Seeing. This technique is called Guiding and requires that the astrophotographer keep constant vigil at the guiding eyepiece of the telescope for the duration of the exposure.
The technical hurdles of precise polar alignment, critical focusing, and guiding are among the most demanding of amateur astronomy's endevours. Try keeping this in mind as you enjoy the astrophotography on these pages.

This is a simulation of what it's like to  guide during an astrophoto exposure. Using an illuminated reticle eyepiece, one must precisely center the guide star,  while correcting  (with a joystick or button controls)  the speed of the right ascension drive motor or correcting  the declination to correct for mechanical errors in the drive or atmospheric conditions.  As the guide star appears to drift away from the center of the reticle box, quick reflexes are needed to return the star back to the center.