The lower section of the observatory
by Bruce Johnston
The lower section was built around nine 4 x 4 posts sunk into the ground three feet and concreted into place. This view of the lower section is as seen facing South. Three 4x4s are used for the East, North and West walls, and four were used for the South wall. The South wall also has posts on each side of the 36" wide opening for the door.
By using 4x4s concreted into the ground around the door opening, as well as at each corner, the lower section became rock-solid and there is no significant flexure of the walls. Goal #2 accomplished!
Two ten-foot 4x4s can be seen on top of the East and West walls. These would become the primary support for the channel iron that the upper section would roll back on.
Here is a view of the same stage of construction, but seen looking East. The plate on the pier can be seen, as well as the fact that the pier is located closer to the South wall, leaving quite a bit of room at the Northern end, where I spend most of my viewing/astrophotography/CCD imaging time.
Final wall height was selected after the posts were buried and the floor joists were screwed into place. I put the LX200 into place on the pier, then measured the needed height for a wall that would allow me to view down to my Southern horizon ... my lowest one... while comfortably standing on the soon-to-be-installed 7/16" flooring.
I decided on a wall height of five feet. Any higher would have obstructed my view, and any lower would have meant that my upper section would have to be taller. The upper section must roll back with, the door opening easily passing over the top of the 'scope, so no matter which combination of upper/lower wall height, the door and walls would end up being the same overall height. I opted for a maximum height on the lower section and a minimum on the upper section, for the sake of weight of the upper section.
Once the wall height was chosen, the posts were cut off accordingly and the remaining 4 x 4s were bolted into place.
The floor joists were 2 x 6s bolted into place, and the studs for the walls also ended up being made from 2 x 6's, although 2 x 4s were originally planned for. The extra floor braces around the pier can also be seen.
As soon as the wall studs were screwed into place (screws and bolts were used in place of nails in most places), the 7/16" wall panels went up. It was still a long way from being done, but it was very comforting to be able to see a semi-finished building.
Another view of the "finished" lower section, but the pier can be seen through the door opening. (Disregard the soda cans sitting on top of it. It was hot out those days!)