The 'Observatory'

The first time somebody new enters the garden I can almost guarantee one of two comments.

"That's a funny looking greenhouse"

Or ....

"Why have you got a bottle-bank in your garden?"
(The shape rather resembles UK glass recycling containers)

What's it made of?

Both the dome and the supporting walls are bolted together from about a dozen fibre-glass panels. The upper part of the wall and the dome rotates on 6 resin roller assemblies, which in turn run on an aluminium track attached to the lower wall.

The initial construction included only one or two wooden struts to support and reinforce the strength of the panels once bolted together. As the dome has aged the panels have gradually deformed in a number of locations, and so further wooden supporting struts have had to be added.

How big is it?

The dome is 10 feet (3 metres) in diameter and just over 8 feet (2.5 metres) high. The opening is a full 30 inches wide (0.77 metres). This might seem excessively wide for an 18 inch (0.46 metre) telescope. In practice it allows me to see more of the sky for pointing purposes, and means that I'm not forever moving the dome as the telescope moves in time to the Earth's rotation.

The professional observatories are white or silver, why is yours coloured?

The professional observatory builders have rather more influence over the local planning authorities than I do.  In order to prevent unnecessary visual intrusion in the (at the time very urban) area area where it was originally installed, a condition of the planning permission was that it should be a specified tone of green. 'Concrete grey' would have been more appropriateto that area, but rather than argue with the planners (never a good plan), green it became.  Since then the dome has had several colour schemes (it currently being blue and black) with it being turned into a giant ‘ladybird’, now in the planning stage for this summer.

Being coloured does make the dome does heat up quite significantly during the day, but I've found that it cools off pretty quickly once opened so it doesn't seem to be much of a problem.

Why a dome and not the shed type buildings that many amateurs use?

There are technical reasons for going for the dome, and an overarching emotional reason.

Technical reasons.

• The open tube design of the NGT is susceptible to stray light. The dome blocks much of the stray light.
• The open tube design of the NGT makes the secondary and primary mirrors susceptible to dewing on damp nights. The dome virtually eliminates problems with the primary but seems to make no difference at all to the secondary.
• The dome offers some protection to both the telescope and the observer on windy and frosty nights.

The most important reason though is emotional - a dome looks like a real observatory.