Louise and I became interested in amateur astonomy in 2000, and by the spring of 2001, we'd built an 8' x 12' roll-off roof observatory. In case you're wondering about the high walls and gable peak, our viewing site is surrounded by trees, so the observatory walls don't interfere at all. It's the best we can do....
|
|
|
The observatory sits on concrete "deck blocks" which rest on the ground; there is no permanent foundation. The steps to the door use pre-cut stringers and treads from Lowe's. The roof is made from a tar-impregnated woven material named Ondura.
Inside there's an 8-foot square observation area, with a 12" concrete pier approximately in the center (Scroll down for additional photos). The floor is isolated from the pier to minimize vibration. A 4-foot wide computer nook occupies the north one-third of the building. We ran a 3" plastic pipe under the floor from the computer nook to the pier to provide a conduit for power and computer cables.
Here we see the 130mm (5.1") refractor pointing high in the southern sky, with the imaging equipment hanging off the back. A separate guider scope and camera sit off to the side; their purpose is to keep the telescope accurately pointing at an object as it moves across the sky. The weights on the right and the small dumbbell beneath the front of the telescope serve to keep everything in balance.
The Astro-Physics 1200 mount was installed in October 2008. Click here for more photos showing how we attached it to the concrete pier.
This is a close-up of the imaging equipment attached to the telescope. The observatory is designed for unattended operation, and all the equipment is connected to the observatory computer.
A motorized Feather Touch focuser precisely focuses the image. The Pyxis instrument rotator positions the camera for the desired target framing. The CFW-10 filter wheel places one of eight color or narrowband filters in the light path. The ST-8 CCD camera is cooled to reduce noise in the image, and has a homemade weight to counterbalance the CFW-10. To the right can be seen the rear of the ST-402 guide camera.
The guide scope is an inexpensive 60 mm f/5 (300 mm F.L.) refractor, and the guide camera is an SBIG ST-402. The guider equipment is installed on one end of a Casady Triad Bar with six pounds of dumbbells on the other end, as a counterweight. For an external guider, rigidity is key – any flexure results in smeared stars in the image. The guide scope and ST-402 camera are securely clamped to the dovetail rail – the camera is not supported by the focuser drawtube – in fact the drawtube serves only as a shield to keep dew away from the camera chip. Focusing is accomplished by loosening the camera clamp bolt, then sliding the camera along the rail, and tightening the bolt. I've been able to achieve FWHM values of about two arc seconds using this method (I can even do this one-handed, with my post-stroke impairement, by jiggling the camera with a T-handle hex wrench in the loosened bolt head – tricky, but it can be done). Once focused and clamped, no further adjustment is needed from one night to the next.
Here is another view of the guide scope and camera on one end of the Triad Bar, with the guide scope counterweights (dumbbells) on the far end.
A kitchen counter across the west wall of the nook holds the computer equipment for CCD photography. Originally installed at a height of 30", the counter is now at 41" to allow comfortable operation while standing. Many times I found myself alternating between the telescope and computer, bending down to view the monitor. It's much nicer to just walk up and have everything at a comfortable height. A $10 metal bar stool is available for longer sessions at the computer. But we usually operate remotely from inside the house or even let the equipment acquire images completely unattended.
In 2008 we took the first step toward upgrading the observatory to operate totally unattended. This is different than remote control. Unattended operation means the telescope follows a predefined plan to acquire a target and take images of it without any human intervention. Remote control, on the other hand, means controlling each and every operation while sitting at a computer inside the house.
ACP Observatory Control software is the key to unattended operation. Prior to an imaging session, I use ACP Planner to select a target and specify the type and number of images desired. Then the observatory computer and imaging equipment are powered-up and ACP is directed to execute the imaging plan. This startup may occur hours before the appointed imaging time, so it's possible to go out with the family for the evening while ACP operates the equipment. The images will be waiting on a shared network drive the next morning.
Click here to read about a little program I wrote to analyze ACP plans and calculate their timing.
Here is a screen shot of the observatory computer with ACP and the imaging software running. I use the webcam view in the lower-left to verify that the telescope is behaving before starting an ACP imaging plan. Then the white light is turned off, and the webcam monitor is shut down.
Currently, I must be in the observatory to roll-open the roof and uncap the telescope. Right now this isn't a big deal, as the observatory is only 50 feet from the house. However we plan to build a new house in a year or two, and the observatory will be 300 feet away, so walking to it will become a non-trivial hike, especially on cold winter nights. The ultimate goal is to motorize the roof and telescope lens cap so they too can be controlled remotely (or automatically by ACP), thus eliminating the need to walk to the observatory for normal operations.
For imaging, we use an SBIG ST-8XM CCD camera, plus TheSky 6 and MaxIm DL on a 2GHz/512MB personal computer. We remotely control the equipment from inside the house using the Remote Desktop feature built into Windows XP Professional. (Before installing a computer with XP Pro, we used UltraVNC, a free program with similar capabilities.) Once the equipment is powered-up and the observatory roof rolled-back, everything can be done remotely (still planned are motors to roll the roof and uncap the telescope, for totally remote-control operation). Category 5 Ethernet cable in a buried conduit provides access to the home network. We tried wireless networking, but were disappointed with slow speeds due to degraded signals.
Important note: The conduit does not include cable for AC house current. It is not allowed to run signal cable in the same conduit as electrical cable, so a second conduit would have been required for that. Instead, we power the observatory with a heavy-duty extension cord run across the ground to an outdoor receptacle on the house.
Originally, equipment power was switched using an
One Ethernet power controller is shown in the left photo. It has eight switched outlets, plus two always-on outlets. The second controller is installed near the observatory computer. Each controller has a built-in Web server. Pointing a browser to its address opens a page showing the state of each outlet. Clicking on an outlet's link turns it on or off.
It's hard to see a keyboard in the dark! Here's our illuminated keyboard, version 2. Four white LEDs, with their rounded ends filed flat to diffuse the light, are glued to a styrene backboard. The LEDs are powered through current-limiting resistors by the keyboard's +5V power from the computer; a toggle switch (far right) turns the lights on and off.
The onset of cold weather brings howls of protest from the rotating machinery in the observatory computer. The hard drive and those cooling fans just don't like spinning up when it's 10°F or colder out there!
To help them along, I installed a heater in the computer. It consists of a 75-watt lamp and a thermostat for a 120V electric heater. A metal shield protects the hard drive directly above the lamp.
The electrical box and lamp holder are standard outdoor items available at home-improvement stores. The thermostat is a Honeywell model CT410A, also available at home-improvement stores. It switches both sides of the AC line, which is a safety benefit. Do not use a regular wall thermostat intended for gas or oil furnaces, or heat pumps. These are designed for non-lethal, low-voltage circuits. Aside from ruining the thermostat, the 120V house current present on such a thermostat's unprotected electrical contacts could electrocute you.
The AC power cord runs through a 1" hole punched in the computer's rear panel. I lined the hole with plastic "grommet strip" to prevent the metal edges from cutting into the power cord, and stuffed it with foam to keep rodents and bugs out.
Before an imaging session, I turn on the heater and let things warm up for a while. The thermostat turns off the lamp when the temperature inside the computer reaches about 60°F. When the computer is powered-up later, all those rotating components sound much happier.
The telescope mount and imaging equipment use external power supplies. I needed a way to keep these and the Ethernet power controller off the floor and to manage the cables. The solution was an equipment holder attached to the concrete pier.
I made four identical plywood brackets with semi-circular cutouts, and clamped them together in pairs around the pier with 5/16" threaded rod. Various ad hoc mounting arrangements support the equipment. The Ethernet power controller is attached with screws, and the heavy regulated power supply for the mount is supported with metal angle brackets. The electric focuser control box is held in place with Velco. "Black-box" power supplies for the CCD camera and other equipment rest on the brackets, nestled near the pier. Large holes in the top and bottom brackets allow cables to pass neatly through.
LHere are a few more photos showing the "critter screen" between the concrete pier and the observatory floor and details of the roll-off roof wheels and track.
|
The critter screen keeps out rodents, snakes, and other curious animals (but not bugs, which come in around the roll-off roof). The screen also catches small parts that drop while working on equipment at the pier. It is attached with construction adhesive to the pier and to the sides of the hole in the floor. 
|
The roll-off roof is supported by six hard-rubber wheels riding on a 2x4 track. a 1/8"-thick aluminum angle on each track guides the wheels. 
|
|
.) |
When closed, the roof is locked in place by a long J-bolt in each corner. The bolts are about 12" long, and have a right-angle hook on one end, and threads on the other end. The hook fits in a hole drilled in the roof structure, and the threaded end goes through an eyebolt screwed to the observatory wall. Gentle tightening of the wing nut is all it takes to hold the roof securely in place. (For high wind, we attach the steel cable visible in the lower-left corner to the large eyebolt in the upper-right corner; the cable is attached to an anchor screwed into the earth.) 
|