I have been thinking again about finally getting my astronomy kit up and running again – so I’m looking into designs for observatories. There are many different types of observatory – domes, roll-off roof, roll-away building, etc, but due to the size of our garden, I think that a dome could be the most desirable option (it has the smallest footprint, has good shielding properties from wind and light, and it looks like a “proper” observatory . Of course, we have to consider what are the downsides: More expensive/harder to make, needs to be rotated every so often (or motorized), and it looks like an observatory rather than a common old garden shed!
Of course, I could buy a commercial product – The pulsar domes seem to be most affordable (ignoring the Exploradome – useless with a German Equatorial mount!), though the 7 foot version is a bit small for my liking – and the 9 foot version is over 3 grand… So, I have come up with some ideas on a DIY dome and they are listed below (in a psuedo-design brief).
Building of a 9 foot diameter observatory dome.
- Fully weatherproof (water/wind proof) – including shutter seal and skirt to avoid water/snow ingress between dome and walls
- Rotates 360 degrees
- 2.5′ door opening (enough for a 14″ telescope?); door to open either by sliding back over roof of dome, or by two doors sliding sideways away from the opening.
- Door opening to extend 1.5′ beyond the zenith
- Ability to securely lock dome in place (no rotation) when not in use, and securely lock doors from outside.
- Mount dome (and associated circular runners) on a solid base (eg breeze blocks laid to circle with mortar)
- Suggestions: Use marine grade plywood to construct frame of dome, and then cover with a skin of weather proof material (eg masonite, painted & caulked and then sealed with multiple layers of urethane paint to weatherproof). Alternatively, a metal skin would be acceptable. (eg: http://www.pictorobservatory.ca/html/pictor.htm; http://www.geocities.com/va3ngc/Astronomy/Projects/ObsDome.html)
- Dome runners – angle iron rolled to circle, run on castors with horizontally mounted guide wheels to keep the ring in place on the runners: http://www.astro-sharp.com/dome_wheels_door.asp
- Dome shutter: – Possible design involving a sliding section which slides back over the dome: http://www.astro-sharp.com/dome_shutter.asp. Bottom portion of the shutter must be removable (rather than flap down as shown) to avoid being fouled by the garden fence when rotated.
- Dome shutter – Alternatively full length split shutters which open to either side of the dome slit.
- Investigate the possibility of incorporating a motor drive into the design of the observatory – this should be able to drive the dome in azimuth in both clockwise and anticockwise directions (motor drive not required at first, but allowing for the addition of the motor drive at a later stage would be very useful).
So the first ideas are pretty much there. The dome itself looks OK, the door/shutters looks tricky, and the motorization is something that I think I will have to look at later… Maybe time to start getting some costs for materials, making some drawings, etc. and possibly worth thinking about getting some prices for parts (eg – getting wooden arcs cut? angle iron track? getting someone to make the whole thing?!?)…