A clock drive is used in astronomy to automatically move a telescope at the same speed as the Earth’s rotation, allowing for steady observation and astrophotography. It rotates the telescope at one rotation per sidereal day, and is now electrically powered. It reduces human error in astrophotography.
A clock drive is used in astronomy, especially for astrophotography. It is a piece of equipment that is attached to a telescope mount. Using a watch with a telescope ensures that the field of view always remains the same or that the telescope moves at the same speed as the Earth so that it follows what is being viewed.
Due to the Earth’s rotation, objects appear to move across the sky over time. Before the invention of clock drives, astronomers would have had to manually move their telescopes to compensate for the motion of the Earth. Watch drives have allowed this to become an automatic movement so astronomers can focus on what they are observing without having to move and refocus their telescopes.
A clock drive is designed to rotate the telescope upon which it is mounted at the rate of one rotation per sidereal day. A sidereal day is the time it takes for the Earth to complete one full rotation from the vernal equinox, or the vernal equinox passing the Sun in March. Each sidereal day is about four minutes shorter than a solar day, or a day measured by the Earth’s rotation around the sun. Sidereal time is used by astronomers to know where to point their telescopes to observe a particular star on any given night.
The original clock drives were often driven through the use of falling weights and a pendulum, similar to what is seen in pendulum clocks. Current clock drives are now electrically powered through the use of a right ascension motor. In most cases, the watch unit is attached to a bracket on the telescope mount. The motor is then connected to the retarder drive shaft, either directly or via a gear system. Attaching the watch unit to the telescope mount means that the mount is moved and not the telescope, meaning that the focus and angle of the telescope is maintained at all times and it is simply rotated around an axis.
A clock drive can be an integral part of equipment for astrophotographers. The slow and steady movement of the clock drive ensures that the telescope is tracking your chosen star smoothly. This in turn allows you to take photographs at different intervals as you watch the star move across the sky. By attaching a clock unit and camera directly to the telescope, the amount of manipulation by the photographer is greatly reduced once the telescope is initially set up. This means there is less chance of human error when taking photographs over a long period of time.
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