BUILDING AN OBSERVATORY

"Southern Cross Observatory" Mark 2

Stage 1.

During my years of amateur astronomy in England, an observing / photographic session during the winter months was preceded by clearing a path through the snow to the telescope. When I moved to Tasmania in 1968 and brought the telescopes with me, I decided that the first priority was to build a small observatory. This was a 10 foot diameter rotating dome of traditional design, and even though it was a little on the small side for the rather large fork mounted 12" f/6.7 Newtonian, it served its purpose extremely well during its years of operation.

After several job moves both in Tasmania and Interstate, I have finally settled in Cambridge, a rural setting with a few acres, with enough space to build a larger observatory more suited to my present requirements. My interest has always been astrophotography of the sun, moon and planets using 35mm film and small plate cameras. My interests are now on various electronic imaging techniques using video and CCD computer controlled cameras. With this imaging technology comes a great deal of electronic equipment that needs space, lots more than I needed in my film photography days. Time to build another observatory!

Design criteria that had to be met were as follows; low cost one man construction, on-site construction with available tools, resistant to minor bush fires, large enough to accommodate all the new equipment, protection from the ever present winds of the "Roaring Forties", and of course room for visitors.

An article in the September issue of Sky & Telescope describing 'An Unusual Observatory Design' by Scott Jamison caught my attention. Even though it was an all timber construction, I thought that I could translate the idea into a similar structure using steel instead of timber. A few basic drawings and a rough cost estimate, and I had a project. This bi-cylinder design is used for some professional observatories.

Three sizes of flat steel and some angle iron for the framework and Colorbond sheeting for the cladding and a treated pine decking floor. Armed with an angle grinder to cut the steel, an electric arc welder to stick it all together, a good builder's level and a water level, I was on the road to having a new "Southern Cross Observatory". Dimensions: Diameter - 4m, maximum height - 2.8m, slit width - 1m, height at front - 1.2m, access door 2m x 1m.

A level site had already been done with a Bobcat, and the substantial 1m diameter steel and concrete base for the fork mounting sunk 400mm into the bedrock. The adjustable base for the fork mounting was then at ground level. A 4-metre diameter circle was marked out, and holes 300-400mm deep around the circumference were drilled into the mudstone. Forty odd steel reinforcing rods were hammered into the holes with 300mm above ground. The first strip of 50 x 3-mm flat steel 12m in length was wrapped round and welded to these steel pegs to form the base ring upon which the whole observatory would rotate.

Another steel ring of slightly larger diameter was formed in the same manner to make the base of the main observatory. Prior to forming this ring, the positions of the eight wheels had been marked out and holes drilled to take the bolts, which would carry the eight flanged wheels. These wheels are flanged and contain two 50mm ball races. The smaller diameter of the wheel is covered in a 12mm thick layer of hard rubber compound. In practice this makes the wheels silent in operation, and the rubber grips the track to provide smooth traction. The structure requires minimal effort to move and a small 12volt DC motor with gearbox and speed control will be fitted for motorised control. A pre-rolled angle iron section of 25x25mmx5mm forming a circle was also welded to the base pegs to act as the anti-lift retaining section. Eight steel straps drop down from the wheel retaining bolts which have a ½" bolt that protrudes under the angle. The flanges on the wheels prevent lateral movement of the structure during rotation.

The two front and two rear angle iron supports for the pre-formed angle iron slit arches were welded to the bottom ring. This formed the basic structure and reference points for the remaining uprights and cross pieces. These were made from 25 x 25 x 3mm angle.

This stage was critical, and assistance from a friend experienced in steel construction, was invaluable. It all had to be square, and four hands were definitely better than two. A good size builder's level was a must. A total of fourteen angle iron uprights with horizontal crosspieces were finally welded in the right place and square on to each other with the base.

To enable the cladding to be attached, four rings of flat steel were wrapped round the uprights at various heights, and welded in place. These rings were made to length (12.56m) prior to wrapping to ensure accurate same size circles.

Prior to cladding and fitting the floor, the whole steel structure has been painted with Wattle Aluminium Epoxy Anti-Rust paint, which over the years I have found works well on bare steel.

The next stage is the floor, which will consist of 50x100mm treated pine joists sitting on small paving slabs, and covered with treated pine decking. This will be easier than getting materials on site to lay a concrete floor, and more comfortable on the feet! A covering of industrial weather resistant carpet will finish off the project.

The sheets of Colorbond cladding have been cut to size, ribbed for the walls and flat sheet for the curved roof and slit opening. This will be attached when the floor is completed and all silver painting is finished. The cladding will need the help of friends. This will be the tricky part due to the fancy curves that need to be worked out and cut for the top of each sheet.

Attached photos are digital still shots from my Panasonic 3CCD Digital Camcorder.

Click on Images for a larger view.

Southern Cross Observatory - Main structure prior to cladding and floor installation.


Vertical and Horizontal angle iron sections with corner braces.


Close up of Flanged wheel on track with anti lift anchor ½" bolt
which locates under curved angle section attached to base ring.

Of passing interest, Mt. Canopus, the main Observatory site for the University of Tasmania, is located on the next hill away from me, and it is pure coincidence that I should build my second observatory close to a complex that I have had association with during it's early years. Even more interesting is the fact that I have been taking time off from my project to lend a hand with the re-location of the Astronomical Society of Tasmania's slide off roof observatory, to the Mt. Canopus site.

January 11-2000
 

Updated Observatory Images

All images © Shevill Mathers - reproduction without permission prohibited

 

Shevill Mathers
Shevillm@southcom.com.au

January 11-2000

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