Collecting  Photons

1) Finding a good site

The ideal site does not exist unless you happen to live in the Altacama desert or in Arizona. So, you have to cope with what you have handy. Furthermore it is probably better to have your observatory nearby your house (usage: most clear nights) rather than far away. In my case I am  lucky enough to live in the countryside. The site is the closest spot I could pick near the house, protected from the nastiest dominant wind (from the north, at my site), and with a good unobstructed view. The location of the budding observatory is marked by the piled concrete blocks.

2) Digging and laying down the foundations

"Run rabbit run, dig that hole and forget the sun..." as the Pink Floyd would sing. The hole for the foundation was about one cubic meter (1.2x0.9x0.9) and at least half of this was excavated in a loose mix of rocks (lots) and dirt (very little). The last 30 cm were excavated in solid rock using only hand tool. It took one month of spare time. Eventually too much was too much and I gave up my target depth (1 meter): this was by far the most unpleasant part of this affaire.

 I made a form with salvaged material to give a shape to the upper part the hole in preparation of the pour. The long edges of the form were carefully levelled since I was going to use the to level the foot of the pier. I drilled four 50 cm deep holes 15 cm from the corner for the rebars. Four holes were drilled at the centre of the foundation for the rebars that will reinforce the pier.

Important: the hole and especially the form were roughly aligned to the local midday so that the long axis run on a east-west direction. This simplified a bit the following procedure to align the pier.

3) Pouring concrete in the rebar cage

The grass that has grown on the sides of the hole witness the excruciatingly long time elapsing from the beginning of the dig (early fall 2004) and the actual pour (March 2005). The picture show one level of rebars that connect the corners to the central bars. Two more layers are already sunk below. The bars have been simply connected with tightened steel wire. I used premixed concrete Leca 4000. This provides optimal strength for this application but is a bi lighter than a more conventional mix. I also throw in the pour a conspicuous fraction of the excavated rocks .

The concrete cured very rapidly and in less of 24 hr was holding the weight of a person.

4) Making the foot for the pier

I used a small square form made of planks to contain the pour of the foot. Since this will be the base of the pillar it is important to care for a good smoothness and horizontality of the surface. A bubble level is very useful to that effect.

Important: I wanted to align the blocks with the north, in order to have a clear reference when sinking the support bolts. Before complete drying of the foot,  I placed a block and aligned it with the Polar star. In a way this was the first astronomical observation made at my new observatory. The block was pressed in the concrete (keeping it level), and this left the trace visible in the picture at left. This was used as a very useful reference to lay down the blocks.

Wait about a week to stabilize the pour. Then the pre-cast chimney blocks are piled over fresh concrete. Each block is carefully seated and levelled, and concrete is poured inside, carefully mixing to avoid air pockets. This process continued in a single day until the last block.

5) Mounting the support plate.

I made the support plate with a section of aluminium bar (30x20x2.5 cm). On top of this plate will sit a slice from a bar (24 cm diameter, 3 cm thick) that will host three threaded holes to anchor the wedge. The support plate received three holes spaced 120° to mount it on the pier. This is done with three 18 mm stainless steel bars 32 cm long sunk in the concrete. I have epoxied two nuts on each bar to help their stability in the concrete. Maybe this was not much but the bars have been sitting on the pier for over a year as I write this and they are extremely stable. The wooden rig on the left was prepared (carefully prepared, actually, in spite of the rugged appearance) to keep the bars aligned with the holes on the support plate. I placed the rig over the last chimney block, carefully levelled it with thin slices of wood and then I poured the last instalment of the concrete mix. I resisted two weeks before taking the frame out and mounting the telescope.

Of course, the three couples of counteracting nuts are regulated to level the plate.

6) Mounting the telescope on the pier.

The pier and the adapting plates are now complete, and the telescope is mounted on the new base. What was left was to verify that the amount of azimuth regulation of the wedge was sufficient to align the RA axis with the pole. Thankfully it was and after a couple of hours of drift alignment the scope was ready to take the first picture at the new site.

7) An observatory without a roof...

...or walls, for that matter. This has been my set up since spring 2005 until the beginning of the construction of the observatory building (May 2006). To protect the scope I use several layers of water proof material capped by a large and very tough green bag. As horrifying as it may seem the telescope has survived a very wet fall, a very cold winter and a pretty horrible spring.