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Building a Backyard Astronomical Observatory

Updated: Jan 17

It took a while to get to this moment. I have been dreaming about having an astronomical observatory in my backyard for a very long time. Finally, I got a piece of land in a reasonably dark sky (Bortle 4), and I also saved enough money to initiate this DIY project.


I usually have meetings until late as most of my clients and colleagues are from overseas. By the time I'm usually free, I'm exhausted and don't feel very enthusiastic about setting up a relatively large telescope for a very short session. The expectation is to get quick access to astrophotography equipment, with everything ready for action and as much automated as possible.


Getting started is quite a challenge for me because I have zero experience as a builder. It represents a massive investment, and I just want to do it right the first time.


This article will capture the whole journey, and it will be updated after every milestone. I hope it will help other people in a similar situation.


The original idea was to build a clamshell dome, but I quickly realized that it was either too expensive or complicated to build as a DIY project. Given my tight budget, my experience, and my building skills, I decided to go for a more traditional dome. This type of observatory is ideal for areas with strong winds, local light pollution, and limited space.


The design is based on Mark Parrish and Steve Richards [2] for the flooring, the wall plan, and dome bearings. I got the inspiration for the structure of the dome from Charles Baetsen's design [3], which is based on aluminium and is very light. The shape of the dome is based on a cross-section sphere like AstroDomes or ScopeDomes. I also got a lot of advice from the amazing community of "Home Observatories/DIY Astronomy Projects" Facebook group and CloudyNights forum. The pier foundation has been validated by a family member who is an architect.

In addition to that, I plan to incorporate automation based on the popular LesveDomeNet Dome Automation [1].


Design

The observatory sits on top of a sloped area located ~2.4m over the ground level. The telescope will be mounted on top of a concrete pier, raising the height an additional ~2.2m. This gives quite unobstructed views of a large portion of the sky. There is another property next to the sloped area, which hides around 12degress in the southwest. So far, I'm very happy about this location.


The inside diameter of the dome is close to 3m while the diameter of the floor is ~2.75m. This gives room for my main telescope (Skywatcher Quattro-10C carbon-fibre over an EQ6-R Pro mount), but I'm still able to host a bigger telescope and have enough capacity for outreach.

I don't expect to go bigger than 16" hypergraph f/3 or Wynne-Riccardi Astrograph f/2.8 working on prime focus and operating on EQ8 mount.

The area inside the observatory is around 5.1m2, which means that I don't need to request consent from the local authorities as it is smaller than the current 30m2 limitation. The center of the observatory is also located 4.5m from the neighbor's fence, and the top of the dome is just one meter higher than the top of the fence, which also follows the boundary rules defined by the local council.


I didn't feel very confident working on the foundation of the observatory. For that reason, I hired professional services offered by Oslu Garden Services Ltd. They are also helping me with other parts of the landscaping. The dome structure sits on top of eight poles of H4 treated timber100x100mm square section anchored with concrete. The telescope pier has a total length of 3.620mm. It emerges from1200mm deep and goes up to 2420mm over the ground. I will use an acrowtube of 300mm diameter and 2620 long to connect the concrete cylinder to a massive 1m3. This will move the center of mass ~0.8m below the ground level and provide extra stability to the mount. The reinforcement pile used is 12mm grade 500E rebar and 3570mm long with 75 concrete over and linked to a rebar mesh placed on the base of the 1m3 of concrete. The base of the pier has been compacted, and it has a layer of 10cm of GAP20 for stabilizing the clay.


The following diagram provides an overview of the concrete pier structure and the depth of the poles located on the sides that support the base. The poles located between the sides have been removed to avoid introducing noise.

Three stainless steel M10 threaded rods a meter long is going to be cast into the pier to provide additional reinforcement and connect to the equatorial mount adapter plate.


Shopping List and Required Tools

In this spreadsheet, I have been incorporating all the expenses related to the observatory, except for the tools used and the astrophotography equipment. I hope this will help others considering to embark on that journey to get a hint on the budget required to accomplish something like that.


This is an almost complete list of tools used or planned to be used to build the observatory.

  1. Marking-out tools: a tape measure is essential, as is a level.

  2. Mixer and barrow: hire a cement mixer and use a wheelbarrow to transport wet concrete

  3. Pegs: make pegs from 1×2-inch timber.

  4. Shutter board and tools: a handsaw, hammer, nails, and a selection of plywood or chipboard pieces.

  5. Spade and shovel for shifting ballast and concrete.

  6. Power tools: a circular saw, router, or jigsaw for cutting the wood (you can hire these tools).

  7. Woodwork tools: a handsaw, plane, hammer, and screwdriver, plus nails and screws.

  8. Tools: hand tools for cutting and fixing the floorboards.

Construction

The reinforcement cage is something not easy to find in NZ. Lucky me, my brother-in-law is a civil engineer, and he provided the directions to build one onsite.

I started with the reinforcement cage for the concrete pier. I hired a rebar cutter and bender from HirePool for ~$28. In less than 3 hours, I had all the rebars cut and bent to build the mesh.

I used some bricks to help me to hold the mesh of the base (850mm x 850mm). That mesh will be covered by 1m3 of concrete with 75mm on the sides and sitting over 14 chairs of 65mm from the bottom.

I also designed, and 3D printed a few copies of a tool for holding the six rebars straight and parallel to create a 75cm ø reinforcement pile. If you have a 3D printer and you want to follow the same path, you can download the STL file from here. This pile sits on top of the previous mesh, as represented in the following diagram.


References

  1. LesveDomeNet Dome Automation: ASCOM dome driver.

  2. Mark Parrish, Steve Richards observatory plans.

  3. Charles Baetsen observatory plans.

  4. A Homemade Observatory Project by Stephen Charnock.

  5. At Home in a Dome by John and Meg Menke.

Gallery

This section contains some photos of the process.



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