Building A Personal Observatory

by Dave Miller
(This article appeared in the November 2007 issue of Astronomy Technology Today magazine)

I remember getting my first telescope, an 8" Schmidt-Cassegrain. It was so much fun setting it up and learning about how all the parts fit together. After getting experienced in setup and use of my equipment, I started to devise way to make the setup and tear down process even quicker. But no matter fast I got at the process, it become one of those mundane tasks that would keep me from nighttime observing on a regular basis.

Many astronomers have similar experiences and end up with the same conclusion that I did - I need some type of permanent setup for my equipment so that I use and start enjoying my nighttime activities again. There are many solutions to a permanent setup for your equipment, but typically the choice comes down to building a roll-off roof observatory or buying a dome. At Durango Skies we specialize in observatories and I get asked which path to go down all the time. Here are my main considerations in helping customers determine which path to take:

1. Amount of space / location - A dome will have a smaller footprint than a roll-off roof observatory. A roll-off needs at least twice its length in space to hold the roof in the "off" position. So a 10' x 10' roll-off roof will need at least 10' x 20' of ground space for construction. A 10' dome on the other hand will need just the 10' of circular space for a ring base and dome. Domes can also be attached to an existing wood deck or concrete slab without much additional construction.
   
   
2. Observatory use - If your goal is to have a place for just you and your equipment, then either a dome or roll-off roof will do. If you plan to observe with family or friends, or to host stargazing events, then a roll-off roof observatory is a better choice. For a given size, the rectangular shape gives you more room than a circular dome and the curved shape of the dome will limit headspace as you get close to the sides of the base structure. Also, it will be much more exciting to point out the wonders of the night sky with the "all sky view" of a roll-off roof than with the "slit view" of the dome.
   
   
3. Type of observing - If you are into visual viewing or astrophotography, then either a dome or roll-off roof will work. And both types of structures can be modified to accommodate a warm or control room. If your observing includes more that one scope to be permanently setup with its own mount, then you will need a roll-roof observatory.
   
   
4. Remote control / automation - If you want observatory automation and remote control, then a dome is the easier choice. I say "easier choice" because most of the major dome manufacturers have the motors and software to rotate the dome, open and close the shutter, and slave the dome to the motion of the telescope. It is much more of a package solution. Solutions designed for domes, such as Digital Dome Works, will work for roll-off roof observatories, but it is still mostly a do-it-yourself setup. A main obstacle in automating a roll-off roof observatory is the position of equipment when in use. With a dome, the telescope sits inside the plane of dome rotation and shutter movement. But with a roll-off roof observatory, the telescope is usually in the path of the rolling roof when in use, so having the roof automatically close without making sure the telescope is in its parked position will have costly results.

Planning

My final step in planning is to put together detailed construction diagrams and a materials list containing all the lumber and other parts required for the observatory. This can take a lot of time and hard work. But the benefit is less time and fewer problems during the construction phase of your project. The last thing you want to find out is that your roll-off roof observatory can't be opened once the telescope is in place or that your dome won't rotate because it does not have the proper support. The detailed materials list can be used to estimate your total cost for the observatory and to get quotes from suppliers. The list will also identify special order items, such as a custom door or roofing material, which may have a several week lead time in ordering.

Telescope Piers

The first step when building your observatory is to get the telescope pier or pier base in place. The two main options for observatory telescope piers are concrete and steel. A concrete pier will be very economical to build when you pour the concrete yourself. The main disadvantage is that height cannot be changed once the concrete is poured, so you need to plan for your current setup, the potential for a larger telescope in the future and maybe a different style of mount. You will also need to figure out how to attach your equipment to the concrete pier. Typically, you embed three (3) threaded adjustment bolts into the top of the concrete and then add an adapter plate. Dan's Pier Top Plates makes adapters for mounting standard SCT wedges and some equatorial mounts, and PierWedge makes an equatorial wedge designed to mount directly to the concrete pier. If you have a different type of mount, then you will need to fabricate an adapter plate for your setup. And don't forget that the adjustment bolts must be polar aligned before the concrete sets.

Steel piers usually cost $600 and up, but have the advantage of being easily modified. Pier manufacturers, such as Durango Skies, have adapter plates for most common scopes and mounts, so if you change to a different mount you just need a different adapter plate. Pier height can be modified if you get larger or different equipment. And if you move, the pier can go with you. Some piers even have a rotating top so that you don't have to worry about polar alignment when the pier is first setup. But, you still need build a concrete base for attaching the steel pier.

Determining the right size (diameter) for you pier is very critical. Don't underestimate the amount of stress a telescope puts on a pier. I remember testing my 12" diameter, 32" high concrete pier with 8" SCT setup by giving it a light kick while viewing with a 40mm eyepiece. I was surprised at how much the image vibrated, although it did dampen almost immediately. The taller the pier the wider the pier needs to be and the more mass into the ground.

Since the concrete pier or pier base will be poured before the observatory is built, calculating the proper height can be a little tricky. If you are going with a steel pier, I like to have the concrete base come level with the finished floor to give things a nice clean look. To come up with this height you will need to total up the floor thickness, floor joist thickness and the distance from the ground to the bottom of the floor joists. The height of the pier, which will govern the height of the telescope, is more of a personal preference. Some people want the telescope lower to the floor so that they can view while comfortable sitting down, while other want the telescope as high as possible to get lower horizon views over the observatory walls. The easiest way I've found to figure this out is to set your telescope on the tripod, get the height that you want, and then measure from the ground to the telescope base. Keep in mind that if you are doing a roll-off roof observatory, you don't want the scope with attached equipment so high that it will interfere with the roof rolling.

One last comment on piers - If you are not ready for an observatory, but want to have your telescope semi-permanently setup, a backyard pier is a great way to begin. I started out this way, with a concrete pier and wedge to mount my 8" SCT. I was living in southern California at the time and had enough room in the back yard for either a dome or roll-off roof, but I liked the yard and knew that I wanted to move some day for darker skies. Southern California does not get much rain and my neighborhood was safe, so I just left my scope mounted on the pier and protected it with a scope cover.

Dome Observatories

If you have decided on a dome observatory, then the next decision is what class of dome you want and the size of dome you will need to house your equipment. There are two main classes of domes on the market today - entry / portable domes and professional fiberglass domes. The SkyShed POD and Explora Dome by Polydome are examples of domes that fall into the first category. These domes are manufactured from polyethylene and give you an inexpensive way of building an observatory to protect your equipment. For each manufacturer there is only one size of dome diameter - 7.5' for POD and 8' for Explora Dome. The SkyShed POD, which I reviewed in the May 2007 issue of Astronomy Technology Today magazine, is a complete package with dome and walls and can be setup in a couple of hours. Polydome offers an Explora Dome option for placing on a wall structure you build, or you can opt for a complete dome and wall package. Prices for these domes vary with the options you choose and the shipping distance, but you should be able to get a basic setup with shipping for under $4,000.

Professional fiberglass and metal domes come from manufacturers such as Technical Innovations, Ash Dome and Astro Domes. These domes come in several dome diameters - 6', 10' and 15' for Technical Innovations, 8' to 30' for Ash Dome and 9.5', 15' and 21.5' for Astro Domes. These manufacturers have fiberglass and metal wall/ring options for creating a freestanding observatory without the need for wood framing. If you want to add your dome to an existing structure, or if you want to create a dome observatory with more room, you can get the dome plus base ring option that will allow you to attach the dome to a wood structure. These manufacturers also have options for dome rotation motors, shutter motors and automation packages for creating a true remote control observatory. Prices for these domes will start at $5,000 and can range upwards of $110,000. And don't forget to include the cost of a deck or concrete slab to support the observatory.

Roll-Off Roof Observatories

If you have decided that a roll-off roof observatory is for you, then you have a lot more decisions to make. Whereas a dome is mostly a packaged solution that you assemble, a roll-off roof observatory is a construction project analogous to building a garage. You get to decide things like the size of the building, the style of floor, color and material for the roofing, style and color for the siding, if you want windows, if you want a warm / control room, etc. Because this type of observatory is built on site, you can tailor it to fit your specific needs, the site location and event the color and style of your house.

One of the first discussion points I have with a customer wanting a roll-off roof observatory is whether they want a deck or concrete slab for the floor. This decision may be dictated by the building site for the observatory. If the building site is relatively flat, then either type will work, but if it is on sloped terrain, then the deck style will be needed. With a deck style floor, supports for a deck are typically 4x4 posts that rest on concrete blocks or are bolted to concrete caissons. These posts can vary in length, giving you to have a flat floor on uneven terrain. If you are building in an area with high winds or on unstable soil, I would recommend concrete caissons for the deck base as they will ensure that your observatory does not move. Concrete caissons extend into the ground to below the frost line or at least a couple of feet, and will have an embedded steel bracket for attaching the deck support posts. A deck is generally less expensive to build that a concrete slab because of the cost of concrete and work necessary to prepare the site for a pour. A concrete slab will afford you extra flexibility for setting up additional scopes on tripods.

There are two main options for rolling the roof - garage door and v-groove rollers. With garage door rollers you can usually find all the parts you need at a local garage door installer. The track is attached horizontally to the sidewalls and the roller/hinge combination is attached to the underside of the roof planks. Once the rollers are in the track, the roof cannot lift off the wall structure, even under high winds. The disadvantage to garage door rollers is that the weight of the roof is not transferred directly to the walls. A very heavy roof will want to twist the rollers upward and places a lot of strain in the steel roller stems and the bolts that attach the hinge to the roof. V-groove rollers on the other hand are bolted to the underside of the roof and ride on top of angle iron placed on top of the walls. This approach transfers roof weight directly to the sidewalls and allows a much heavier roof to be supported. The downside is that a high wind will lift the roof off the tracks, so the roof must be tied down to the wall or roof support structure at all times. The roof on a large the observatory will be heavy, but I've been able to move 10' x 14' and 12' x 16' observatory roofs by myself and I'm 5' 10" and 160 lbs.

Conclusion

If you are looking for a home observatory, there are many options today, at various price points, to meet your needs. The key for determining which style of observatory is best for you is to map out your current and future observing needs. And the key to successfully getting your observatory built is to nail down all the details on site location and observatory design.

Give us a call at Durango Skies and we will design and build your observatory for you!