The Telescope

In this chapter I describe a typical observing session with the 8-inch (20-cm) Thorrowgood refractor at the Institute of Astronomy in Cambridge. The telescope belongs to the Royal Astronomical Society but is on permanent loan to the Cambridge University Astronomical Society and has been on its present site since 1930 (Figure 21.1).

It was built by Cooke in 1864 for the Reverend W.R. Dawes who did not have much opportunity to use it. It passed through the hands of W.H. Maw, a founder member of the British Astronomical Association and an active double star observer, before ending up in the possession of W.J. Thorrowgood, who, in turn, bequeathed it to the RAS.

The telescope is on a German mount and is driven in RA by a small synchronous electric motor. The focal length of the object glass is 114 inches giving the telescope a focal ratio of just over f/14 and a scale at prime focus of 71.2'' per mm. There are slow motion controls in both RA and Dec each of which run on tangent arms and consequently have to be reset every night or two. The telescope can be used either side of the pier but my own practice is to work on the east side of the pier since clamping the telescope this side is much easier and speeds up observing. In addition, the slow motion controls are to the right of the eyepiece and are more comfortable to work with.

Figure 21.1. The

8-inch Thorrowgood dome. (D.W.Evans)

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