Grasslands Observatory - Essays - The Semi-automation (Remote Control) of the 3towers Observatory

The Semi-automation (Remote Control) of the 3towers Observatory

By Tim Hunter

CCD Imaging

The 3towers Observatory was originally designed for visual observing. The optical quality of its Meade LX200 12-inch telescope is quite good. The ten-foot Home Dome used for the observatory is convenient for one or two observers and offers great wind protection. Its large 36-inch shutter opening provides a 360 field of view, allowing for up to two hours of observing before the dome has to be rotated. A roll-off roof observatory would give a better view of the night sky, but the homeowner’s covenants in my neighborhood do not permit a roll-off roof observatory. The local seeing at the 3towers Observatory is average or below average, though there are occasional times of good seeing that permit excellent planetary observing. The dome does not cause excessive heat build-up during the day, and the telescope can be cooled to the ambient evening temperature in less than an hour.

The 3towers Observatory functioned quite well for visual observing for several years and was easily converted to CCD imaging in June of 1998 when an Apogee KX260 CCD camera was purchased. The Meade LX200 12-inch telescope guides accurately enough that one-minute exposures with the Apogee KX260 CCD Camera often show no trailing. The camera is a delight to use, because it is reasonably sensitive, and because its 20 micron pixels are well suited to the focal length of the LX200 either at its normal f/10 ratio or at a reduced focal ratio of approximately f/6.5 using a Meade focal reducer. The one-second read out time of the camera allows one to acquire objects and focus in near real-time. Testing has shown the KX260 camera can record recognizable 17.5-18.0 magnitude stars in a one-minute exposure. To record fainter stars or faint nebulosity, it is necessary to use longer exposure times.

In April 2000, a new CCD camera system was ordered for the Grasslands Observatory, and the Apogee AP7 camera that had been in operation at the Grasslands Observatory was relocated to the 3towers Observatory in early September 2000. While the KX260 CCD camera is a pure joy to use, it does not have the quantum efficiency of the AP7. The AP7 has a somewhat longer readout time making centering and focusing more difficult. However, it makes up for this disadvantage by permitting greatly reduced exposure times and fainter limiting magnitudes in comparison with the KX260. The Meade LX200 telescope can sometimes track up to four minutes without objectionable trailing. However, it is difficult to get consistently good tracking with exposures longer than 60 to 90 seconds. Therefore, I usually take a series of one-minute exposures and add them together using a median routine in either Mira or MaxIM DL/CCD.