ABSTRACT
A "model" in the instance refers to a complex multi-variable equation that correlates the mechanical properties of the mount and telescope with an aligned star database and the optical characteristics of the Earth's atmosphere. There are two types; a pointing model and a tracking model. A significant difference between the two model types is a mount using a pointing model tracks with the right ascension (RA)axis only and to eliminate drift during an unguided exposure it is necessary to accurately polar align the mount. A tracking model uses both RA and DEC motors and will effectively eliminate drift and periodic error during tracking. Plate solving is the most expedient method to compare the apparent and actual position of sync points with which to calculate a pointing or tracking model. Plate solving is carried out in the PC. The major consideration is the refraction caused by the atmosphere. There is no image shift at zenith but progressively more towards the horizon.
