|Hall's Harbour Observatory, Hall's Harbour, NS|
Observatory Construction Blog (2013)
|17-Dec-2018, 10:54 AST||17-Dec-2018, 14:54 UTC|
I have decided that I want an observatory. It will be a dome, rather than a roll-off roof observatory. Probably an 8-foot ExploraDome on a 10-foot square building. It will have power, ethernet, and spare cables from the house, and will be set up to allow remote-control access from the house.
Here is what I am working with right now, and what I hope to have in the future:
I am hoping that I will be able to start site preparation in summer 2013. If all goes smoothly, I could be observing from the new observatory by the end of 2013.
I have started design drawings for the deck, building and pier. The pier will be the first component built, but its dimenstions are detemined by the rest of the structures, so detailed drawings are necessary.
I have been giving some thought to the pier for the observatory. My initial plan was for concrete, but that would commit me to a specific height. A steel pier on a concrete base allows the pier to be replaced if a different height is needed. I thought that I could build a wood mockup to check the height before having a speel pier fabricated.
Now, my plan has evolved to making the final pier itself out of plywood. Plywood is very stable, and a tapered square plywood column would be extremely rigid. Plywood has the advantage that I can make some adjustments in height before finalizing the construction (assuming the adjustment involves a height reduction!).
It is now official: we have purchased a house and acreage in St Bernard, Nova Scotia. This is the future site of the observatory.
It is in a "gray" zone (Bortle 2) on the light pollution scale, which means that it will be quite dark!
Someone sent me an interesting article today, all about the "darkest skies in North America". Guess where: Digby and Yarmouth Counties in Nova Scotia.
I am sure there are areas in Northern Canada, for example, that compare favourably, but in terms of the Bortle light-pollution scale, Bortle-1 ("black") is as good as it gets.
The Baie Ste. Marie Observatory will be right on the edge of this area. We are about four kilometres into the "gray" area, but I am not complaining. It will be a great location for star parties.
My wife and I arrived at our new property today for the first time together. (I have seen it previously on my house hunting trip.) It is as good as we thought it would be. The observatory site will be perfect. Moderate obstructions to the south-east and north-east, but clear views from south around through west to north.
I'll have to wait for my tools to arrive before I find out how the subsoil is for digging foundations and trenching.
Photos in a day or two. I wasn't expecting to be online yet: our internet connection isn't scheduled to be hooked up until next week, and the housekeeping cottage we are staying at doen't have Internet. However, I'm getting a strong signal that isn't password-protected from somewhere!
I was able to try out the new observatory site last night. I have not yet unpacked the scope and all the gear, but I did get out the 20x80 binos and a tripod. Unfortunately, the Moon was just past First Quarter, so there wasn't much to see. I had a look at rapidly-fading Jupiter, Saturn, and the Moon.
The nice thing about the session was seeing how the site worked: really well. There is one neighbour with a big yard light about 1000 feet away, but it is partly obscured by trees. I will be able to block it entirely with a screen. Eventually, the dome will block it most of the time. There are no other lights around. I can see streetlights from a couple of little villages 5 - 10 km away, across the Bay. That's it!
Our local village, Weymouth, is over a hill and behind forest, and it's not big enough to produce much sky glow. Likewise for Digby, the nearest town, which is about 40 km away, and not big enough to create serious LP.
So, when that Moon goes away, it is going to be seriously dark around here!!
This week, I tried out the observatory site for the first time. It took two attempts to get my first image. On Sunday evening, the sky was beautifully clear, but the wind was blowing a gale. There was clearly no way to get an image, so I settled for visual observing.
Thanks to now having a view of the southern sky, I was able to bag several new Messier objects that had been hiding behind 120-foot douglas firs on Denman Island.
On Tuesday evening, the wind was lighter, and I was able to get a decent image. The wind was still a factor, and my guiding was all over the place. No one was more surprised than me when I ended up with my best ever M51 shot.
Yesterday, I broke ground for the observatory by beginning to dig the trench for the power and network conduits.
I hand-dug a pit at the base of the barn wall, where the conduits will enter the barn. The barn isn't really part of the observatory project. However, in order to avoid a retaining wall between the house and the observatory site, the trench will have to dog-leg to within a few feet of the barn. It makes sense, therefore, to make the turn right at the barn and have electricity available there too. So my hand-dug pit is at the junction of the two straight trenches.
I then decided that my back would appreciate some help from power tools. So, tomorrow, a mini-excavator is coming to do the rest of the trenching. So today, I spent a couple of hours getting the ground ready.
I marked out on the ground where the building will go, and removed the surface materials from the excavation areas: the pier footing and the trench. The site is a perfectly level pad of compacted gravel and sand originally built as a bocci court. I want to disturb it as little as possible, since it will make a perfect observing pad if I ever host a star party. By removing the surface materials by hand first, I will be able to replace them after the excavations are back-filled.
I had an interesting discussion with a fellow about the pier footings. He is a carpenter currently working on some trim in the house, but he was also the builder who made the bocci court for the previous owners. He knows exactly what is under the surface. Apparently it is several feet of very thoroughly compacted gravel. He figures that excavating for the pier footing will make a heck of a mess, and that the existing materials will be as stable as any footings.
So his suggestion is to pound four 4-foot-long bolts into the gravel substrate (not sure yet if this is do-able) and to bolt a steel plate to the tops of them. Interesting!
Am I ever glad I decided to go with the mini-excavator for the service trenches!
Halfway along the first of the two trenches, the machine started pulling up huge boulders. Had I been digging the trenches by hand, I would have broken my pick, not to mention my back, and I would have had to call the excavator guy anyway.
So, the conduits are in place. I installed a 1.25" conduit for the electric service and a 1" for the network cables. I plan to install three network cables between the observatory and the house, and another two between the observatory and my weather instruments.
I will finish off the conduit ends with a small amount of hand-digging and back-filling next to the building foundations.
The next job will be installing bolts into the ground for the pier base. There's a guy coming next week to help with that, since the presence of large rocks makes a drill necessary.
Yesterday, I had a crew on site to drill holes for the pier anchor bolts. Based on the topsoil and subsoil information from the builder who originally created the observing pad, I decided to go with anchor bolts driven down into consolidated subsoil below the frost line. The pier will sit on the ground, rather than being supported by the bolts, in order to minimize vibration. The bolts are there to secure the pier and prevent gross motion.
Using a pneumatic rock drill, the crew drilled down about three feet. Then the builder and I cut some 1.25" threaded rods to five-foot lengths and sharpened the points. We then drove them into the holes with a 20 pound sledge hammer until they were four feet deep. They aren't going anywhere.
Today, I backfilled the area and tamped it down. Next will be a base plate made from two layers of 3/4" plywood, which will be fitted over the bolts. The pier will be constructed on that base plate.
I also fished rope through all the power and network conduits in preparation for pulling cables. I still have to complete the condits to the house and back-fill that excavation. Then there is some landscape restoration to do.
I heard from the Exploradome people yesterday. They expect to ship my dome next week. Woo-hoo!
Visible progress! I have completed the grade beam that forms the foundation of the observatory. It is made from four 6x6 pressure treated beams, with lag-screwed half-lap joints at the corners. The corners are spiked to the ground with 18" iron spikes.
Checking my joist layout, I see that the four bolts for the pier are farther apart than I had wanted, so I will have to modify the layout slightly. But I think it will work with some minor modifications. The electrical and network couduits come up in the far right corner.
The next step will be to make the base of the pier. Because of the spacing of the pier bolts, the pier base won't fit over the bolts once the joists are in place. I could make the whole pier before installig the floor, but I want to be able to fine-tune its height based on the floor and wall heights. I think if I install the base now, I will be able to build the rest of the pier later.
I had a productive day today. The floor joists are framed in, and the base for the pier is installed.
The base of the pier is made of two layers of 3/4" plywood glued and screwed together to form a 1.5" thick square. It rests on the ground, on block feet made of 2x4s. Being supported by the ground, rather than by the big bolts ensures that there is minimal vibration. The bolts are there just to prevent it from sliding or tipping. The handles are there because the pier base is a tight fit in the opening in the floor. If I ever want to remove it, the handles will prevent skinned knuckles.
With a string of good weather, I'm making a lot of progress. Today, I installed the sub-floor conduits for AC, DC, and USB to the mount, and then installed the floor.
I came up with a scheme to ensure that the conduits running to the pier don't transmit vibrations from the floor. Instead of attaching the conduit to the underside of the floor, I attached it only at the outer end. At the inner end, it is attached to a large block resting on the ground. This ensures that very little floor vibration is transmitted to the conduit, and even less gets through to the pier.
No progress today. It was a nice day, but lawn mowing took precedence.
Here's what the observatory will look like when completed.
Today's work included screwing down the floor and building the first wall. I still have about 1/3 of the floor to screw down.
In other news, my Exploradome should ship on Monday. Yay!
Slowly, but surely, the building is coming together. The floor is now fully screwed down, and the second wall is up
With another fine day, I have finished the walls. The next step will be to frame the dome support rafters.
Today was a nice day, but I wasn't able to get any work done on the observatory. Instead, I had to take a flat tire into town to be fixed and then mow the lawn. However, I have been busy the last few days, and today I remembered to pull the tarp off the building to take a photo.
The roof / dome support structure is framed. That completes the structural work. I will be wrapping the building in Tyvek before the dome goes on. Next up is the electrical rough-in, followed by (or concurrent with) building and installing the pier.
Today, I finished the last sheathing details and wrapped the building.
I finished the electrical rough-in today. It is fairly complex, because I have two separate mutually-exclusive lighting systems for red and white light, as well as separate circuits for electronics (computers, mount, cameras, etc) and other stiuff (lights, vacuum cleaners, etc). I have lots of outlets on each circuit.
Of the two conduits coming up through the floor, the one on the right is for power, and the one on the left is for network cables. I will have an ethernet cable and an auxilliary cable (phone, alarm, spare) running to the house, and two cables to my weather instruments.
This evening, I set up the scope in the observatory, just on the tripod, to get an idea of how high I will need the pier to be to see out the dome slot. It looks like 52 inches is the magic number, from the pier base to the base of the mount. That's only about 1 foot higher than I am used to having it, so not too bad.
Nothing photogenic to report today. I did some site cleanup and started the detailed pier design, now that I have measurements.
My major achievement was pulling the electrical cable from the house to the barn. Actually, the more appropriate verb is "pushing": it's easier to push the cable into the conduit than to pull from the other end. Whatever you call it, the first leg is done. Today, I'll run the other leg, from the barn to the observatory.
Today, the UPS guy delivered my porch lights. There will be one by the door of the observatory, and one on the rear wall, to illuminate the rest of the observing pad. Both will have red bulbs in them. They are advertised as "dark sky" lights: the shade is opaque and eliminates almost all horizontal and upward light. It's not quite a full cutoff light - the tip of the bulb peeks out - but close to it.
For anyone interested, the brand is "World Imports", and they have several models in the "Dark Sky Collection". I ordered them from Home Depot. I also want to get an almost-matching motion-sensing light for the security system, but it is not available online. It will have to wait until I want to do a half-day drive to get to the store.
I now have electricity in the observatory. I haven't yet fully trimmed out the electrical work, but I have one live outlet. No more extension cords across the lawn!
I also laid out the entrance deck, ready for assembly tomorrow. It may sound like an extravagance, since I have a nice level pad around the building. But the pad surface is a really fine sandy gravel that gets wet from ground moisture after dark and sticks to everything. Just reasonable cleanliness in the observatory requires that I have a deck with a mat where people can wipe off their shoes.
A short work day today, as we had a concert to go to this afternoon. But I was able to get the entrance deck completed. The inboard end is nailed to the building's foundation beam. The outboard end is nailed to the ground with 8" long spikes. The joists rest directly on the ground.
A big day! The dome arrived today!
I got the phone call this morning that the dome was in Yarmouth. After discussing logistics on the phone with the trucking firm, they ended up driving the dome up on a flatbed trailer. Much thanks to the manager, Steve, who came in on his day off and drove the dome up with his personal vehicle and trailer.
After consulting online with other ExploraDome owners, the best advice for unloading it was to just push it off the trailer. Which is what we did, with the help of a neighbour.
So now, my priority is to get the dome installed.
Today was very windy. Rather than remove the tarp from the observatory building and work on the roof and dome, I decided to work on the pier. It was slow work, because I want it to be precise and sturdy.
After spending a lot of time making a tapering jig, I ended up abandoning it and cutting the side panels freehand. I left 1/16" extra on each side, to be sanded off once the column is assembled.
The base is a double layer of 3/4" plywood, glued and screwed together. It has holes in the corners to fit the four bolts that were driven into the ground. There are feet underneath for better support on the ground. The feet extend under where the plywood column sides will rest, so that there is no weight cantilevered on the overhanging corners.
On top of the base is another 3/4" panel to which the sides of the column will be secured.
The pier top took a fair amount of work; it is not just a square of plywood. Besides the three mounting holes, which had to be oriented so that the pier cap will face north, I had to carve recesses in the top for the heads of the bolts that hold the two plates together. The recesses had to be elongated and curved, so that the cap can be rotated to align with north. There is also a 2.5" hole in the centre of the top panel for the big star nut that secures the mount to the pier cap.
Comparing the top and the base, you can get an idea of the taper of the column, which will be 51 inches high.
I had a bit of a flood overnight. Unforecast heavy rain overnight leaked through the tarp, soaked the observatory floor, and seeped into the crawlspace. The hardware for mounting the dome ring was missing from the original shipment, but is now on its way. The sooner it gets here and I get the dome on the building, the better.
Yesterday and today, I worked on the pier. It is finished, and ready for painting. The observatory floor is about 1 foot higher than the workshop floor, relative to the pier, so it's not quite as tall as it looks. One view below is with three sides on, showing the internal structure, and the other is of the final assembly. The window at the top is to provide access to the bolts under the pier cap.
My dome ring brackets finally arrived!
With the ring temporarily supported at the proper height, I resumed installing the roof panels. I can't tell you what I think of the roof panels, this being a family website. They have corners that are 85 degrees instead of 90 degrees. There are no straight lines, even where there should be. And they are too stiff to bend into shape by ordinary means. About the only thing that might have made them fit would have been four giant 12-foot pipe clamps to clamp around the whole building. I wrestled and cursed and finally got them on, but it ain't pretty. A am already thinking that, next summer, I will replace them with plywood panels.
Anyway, that's done. Sort of. Tomorrow, I have to caulk the seams, which can't really be done until there are enough screws installed to hold the panels in place.
Then, it'll be on to more fun stuff. I have to attach the ring, using the brackets that arrived today. Then install the rotation wheels, the upper ring, and the dome itself. With any luck, I should have the observatory under cover before the rain that is forecast for the end of the week.
Woo-hoo! I got the lower ring bolted down, the rotation wheels installed, and the upper ring set in place. It was only 2:00 pm, and, with rain in the forecast, I decided to press ahead and install the dome. My neighbour was willing, and - bonus! - he had a helper with him. In no time at all, we had the dome in place. I now have the dome secured with its retaining ring segments. With the exception of the door, over which I have hung a tarp, the building is weathertight.
I then installed the pier. It is now bolted down and looks good.
With the big skylight now covered, my next step will probably be lighting.
Nothing major to report on the observatory. I am puttering away on all the little things that need doing.
I have installed the last cable (a control cable for the future rotation system), so I can close up the walls. I am using pegboard for the interior walls as a compromise between a finished appearance and thermal ventilation for the wall cavities. It will be attached with screws so I can access wiring for upgrades.
I figured out my DC power system design and ordered components. I will have a 30 amp regulated DC power supply wired to a multi-port junction box on the pier. I am using Anderson Powerpole connectors, and will be making up custom power cords for all the 12-volt devices.
There will also be AC power at the pier for those devices that don't use 12 volts DC. Both the AC power and the DC power to the pier will be switchable, both manually and by the computer, so that I can power-up and power-down remotely. The wiring for all that is in place, so I have now closed up the floor access panels around the pier.
The last couple of days, I have been making the door. The door and frame have been assembled, fitted, disassembled and painted. I installed it today. Installing doors is fiddly work even for experienced carpenters, which I am not. But eventually it worked. All the hardware is installed and working, so I can now lock the building.
Next, I have to look into exterior siding.
I tested out the mount on the pier. I probably should have made the pier a few inches taller: the sill of the dome slot is higher than I anticipated, so I can't see quite as close to the horizon as I would have liked. However, stuff that low is pretty murky anyway in this sea-level sky.
The pier is solid. If I rap it on one side, I can feel a bit of a "ring" on the opposite side: about 15-20 Hz for half a second or less. It is very low-amplitude; I can feel it, but not see it. I'll see when I put the scope on it, but I am happy with how quickly the vibration damps out. I don't plan to rap on the pier when I am imaging!
There are still a million and one things to do, but I am getting there. Weather permitting, I may be able to try it out around the next new moon.
Today I finished the exterior siding. I used vinyl siding because it is inexpensive and easy to install. It is a functional building, so the fact that it looks all right is a bonus.
I still have a few details to paint. There are wood inserts where the exterior lights are mounted and a toe-kick under the door that need painting.
The exterior lights are installed and functional. There are two lights at the door: one a white-light motion-sensing security light and the other a red-light fixture for when the observatory is in use. Both are intended to be full-cutoff fixtures, as all outdoor lighting should be. In practice, the shade on the red-light fixture is a little too short for the bulb, so it is only a mostly-cutoff fixture. There is a similar red-light lamp at the back of the building to illuminate the observing pad.
All lights, interior and exterior, are controlled by a master switch, so that white lights cannot come on while red lights are selected and vice versa.
The second image below shows the observatory site, looking towards the north-northwest, over St. Mary's Bay (Baie Ste. Marie). The corners of the building point almost exactly towards the four cardinal directions. The far corner is north.
It is official: the Baie Ste. Marie Observatory is open!
Yesterday, the final components arrived in the mail: the 12-volt power system. I had spent the week finishing the interior with pegboard on the walls and ceiling, and completing the electrical trim-out. I built a workstation for the laptop in one corner. The only thing left to do was the DC wiring.
I have two 12-volt DC power supplies: one that I picked up in full working order from a junk shop, and the other that arrived in yesterday's mail. The junk-shop power supply will provide power for relays that will allow the computer to switch the mount and all the astro-electronics on and off. It will also operate the dome controls when I install those as an eventual upgrade.
The new power supply will power the mount and cameras. Both power supplies feed power separately into the observatory's built-in wiring through a wall-mounted faceplate. The mount wiring goes under the floor to a distribution box on the pier, where all the electronics get plugged in.
By yesterday afternoon, I had moved in most of my equipment and had everything hooked up ready for an evening of observing. Amazingly, the weather was clear!
Let me tell you that having an observatory is a real treat! I wish I had had it years ago. No more lugging eight loads of equipment outside. I just opened up the observatory and flipped a couple of switches and I was ready to go.
The most important task was to do my polar alignment. Now that the mount is set up permanently, I won't have to do it again. I did my normal polar-scope alignment and then started observing. Later in the session, I did a drift alignment, since I want the setup to be asaccurate as possible. It turned out that the drift alignment couldn't improve on the polar scope alignment: it was already right on.
I was doing visual observing only last night. I spent the evening looking at some old favourite Messier objects, as well as Uranus and Neptune. I will set up the camera tonight.
It is great having a clean, dry workspace. I can set eyepieces down on a shelf. Equipment doesn't get covered in dew. With no wires on the floor, I can move around without fear of tripping over something.
Copyright © 2015 Kathleen Walker
Last modified: 27-Dec-2015