In Search of Dark Skies - My Search Is Over - GifNet.US Observatory

[chris_g]

Downsized the layout and kept both OTAs in play.

[chris_g]

Sorry Chris, I meant to answer this question but it got set aside and then I forgot. I'll try to get to it tonight or tomorrow.

That's ok, made my brain work. I actually figured out a math discipline that I didn't totally f off in school that would provide the answer other than trig! Geometry and the simplicity of a right triangle and it's hypotenuse!

[Graeme1858]

That's ok, made my brain work. I actually figured out a math discipline that I didn't totally f off in school that would provide the answer other than trig! Geometry and the simplicity of a right triangle and it's hypotenuse!

For some strange reason I always remembered a mnemonic our maths teacher taught us in secondary school:

Should Old Harry
Catch Any Herring
Trawling Off America

So in a Right Angle Triangle:
The Sin of an angle is equal to the Opposite side divided by the Hypotenuse
The Cos of an angle is equal to the Adjacent side divided by the Hypotenuse
The Tan of an angle is equal to the Opposite side divided by the Adjacent side

Funny what sticks in your mind and what you forget! I used it to work out the height my observatory pier and walls had to be.

Graeme

[SkyHiker]

What is the roof shape going to be, flat or a gable roof? Is it the same for dark room and observation room?

I did a simulation for the case of a gable roof for both rooms, with a gable height of 0.25 times the wall width, assuming that you roll the roof off to the point where the West gable hits the East wall. I used the mount parameters that you mentioned, assuming that you referred to the height of the mount as the top of the pier section, 94". I used the RA and DEC sections same as on my G11. I assumed a GSO F/4 12" Newt for the OTA, just to be on the safe side in case you ever decide to get a big scope.

For this case the clearance is about 33, 36, 37, 22 degrees on the S, E, N, W sides, for the East-side mount. For the West-side mount, flip the E/W values. The X and Y scales are in meters, X runs from East to West, Y from South to North.

I can easily run it again if my assumptions are wrong, if you like.

[JayTee]

Downsized the layout and kept both OTAs in play.

A couple of things I noticed: I found that having more than one door to the outside was key, mainly for moving gear in and out, also I think the gap between the pedestal and the concrete pad should be relatively small. The bigger it is the more likely you are to drop something into whatever is covering up that "large" opening. To minimize this gap my pad has a circular opening for the pedestal.
Just some thoughts.

Wall heights:
Also, my wall heights were based on the 50% rule. At what point does my head hit the roof (now closed) because it is lower than the top of my head? I live fairly far North and I need my southern wall to expose the southern sky all the way down to the horizon. Ioptron only sells a 900mm pier so that kind of set everything else in motion. That drove my southern wall to be 4' high. the pedestal height, plus the pier height, plus the mount height, plus the OTA attached height, all contributed to making the northern wall 7' high, which coincidentally means my head hits the roof about halfway down.

[chris_g]

What is the roof shape going to be, flat or a gable roof? Is it the same for dark room and observation room?

I did a simulation for the case of a gable roof for both rooms, with a gable height of 0.25 times the wall width, assuming that you roll the roof off to the point where the West gable hits the East wall. I used the mount parameters that you mentioned, assuming that you referred to the height of the mount as the top of the pier section, 94". I used the RA and DEC sections same as on my G11. I assumed a GSO F/4 12" Newt for the OTA, just to be on the safe side in case you ever decide to get a big scope.

For this case the clearance is about 33, 36, 37, 22 degrees on the S, E, N, W sides, for the East-side mount. For the West-side mount, flip the E/W values. The X and Y scales are in meters, X runs from East to West, Y from South to North.

I don't know what the roof shape is going to be yet. I'm leaving the roof design up to the construction company. I'd prefer a roof that slides back over the west. I've seen a design where there are two separate roofs, that would support sliding off to the east, that would also be easier on the motors since they would only be moving 15 feet of roof instead of 20.

Mount height is not to the top of the pier but to the center top of the mount saddle. So, my hypotenuse angle did the trick. Your simulator confirms it, awesome!
SC01 - EQ6-R minimum pier height is 36.4", max height = 56.4", C8-R
SC02 - AZ-EQ5 minimum pier height is 41", max height = 48.7", WO Z73 (not sure where I got the max height of 43 from, bad web search)

Thank you for the simulation, now I know why one design I saw was 11.5'x15.5'.

Height=7, length=11.5, hypotenuse angle = 31.3

One more simulation please.
Distance from N and S walls 4.25'
E and W walls 3.75'
mount height 49"
assuming a gable roof.

If I'm seeing this correctly in my head, the simulator results should reflect values closer to 30.

Clear Skies,
Chris

[SkyHiker]

Because you specified the saddle height (presumably in the home position), I had to lower the pier height that I had set too high, which means that the OTA is lowered by 26 cm. That resulted in a saddle DEC height in the home position of 49.6", close enough. Despite the other changes the numbers increase: 37, 44, 42, 27 degrees for S, E, N, W.

Of course, one of the main causes is the assumption of a gable roof, its size and the assumption of where the roof goes (that I left unchanged). It's best to decide that with your contractor first before we can conclude if this simulation scenario is worth anything.

Let me know offline if you want to try the Chris-custom script. I made the dimension parameters easier to understand and modify.

[SkyHiker]

Just a thought: If you want to minimize the blockage by the gable, it is best to make the rails in the South to North direction. That should eliminate the gable on the East side that you would otherwise have. Nobody does it that way AFAICT but why not - the rails are shorter that way, too. To not have a gable on the warm room side you could make that roof section single panel slanted, going up from East to West. When you close the roof that slant will look a bit odd, but it will give you the maximum clearance. Or you can make it a flat roof, but then you have to worry about sagging and water runoff issues.

[chris_g]

Because you specified the saddle height (presumably in the home position), I had to lower the pier height that I had set too high, which means that the OTA is lowered by 26 cm. That resulted in a saddle DEC height in the home position of 49.6", close enough. Despite the other changes the numbers increase: 37, 44, 42, 27 degrees for S, E, N, W.

So, these numbers are for a mount height of 49.6" + your OTAs height at total distance from N and S walls is 6.75', from the E and W walls 5.25' = 37, 44, 42, 27 degrees for S, E, N, W.

So, not a big enough expansion to accomplish anything, so I am thinking now back to the original design and use the tripod's flexibility of adjusting the height to reach that 30-degree FOV. Here's a thought, can you plug in the original numbers in the simulator, then adjust just the height until you get the answer? Your assumptions on gable height are good enough for me.

Appreciate this...

[chris_g]

I just thought of something, the EQ6 on tripod is the last thing not packed. Hmmm, how difficult would it be to set it up? hmmm, I wouldn't even have to connect to it to a computer. I could manually move the mount to the home position, put a led laser in the saddle, adjust the pitch to 30 degrees and move the mount backwards from the wall until the flashlight illuminates the dot at 7' on my 10' wall.

Distance from wall needed to spotlight 7' point = 54" at a 30-degree pitch. 4.5 feet. Original 10x15x7 design works.

I know it's not very mathematical other than I used a ruler to put a point 7' up on my wall and I even think someone said measure it, LOL!

Distance needed = 3 feet, but this one isn't the one really needed

This is the one really needed, distance = 4.5 feet

I should be closing in about two weeks on the new place, my property lines are in green, the blue are planned buildings, the Observatory and outdoor pad are farther to the back. The red is my neighbor's place. I'll start updating again once I've got a construction company on board.

Clear Skies,
Chris

[SkyHiker]

Just a thought: If you want to minimize the blockage by the gable, it is best to make the rails in the South to North direction. That should eliminate the gable on the East side that you would otherwise have. Nobody does it that way AFAICT but why not - the rails are shorter that way, too. To not have a gable on the warm room side you could make that roof section single panel slanted, going up from East to West. When you close the roof that slant will look a bit odd, but it will give you the maximum clearance. Or you can make it a flat roof, but then you have to worry about sagging and water runoff issues.

Let me clarify my last post, here's what I had in mind. The observatory room is 10 x 13 x 5.5, warm room is 10 x 5 with a 5.5 foot East wall and an 8 foot West wall. The mount is offset 0.5 foot South of the North-South center. The 2 mounts have 5' center distance. The mount can easily be parked.

The roof slides off to the North. That way you can have a gable roof with no blockage issues because the roof sections are all slanted at 30 degrees.

I have a 5.5' lower wall and 7' higher wall myself; it does not give me a cramped feeling when setting things up. If the goal is to give a tour, that will be harder but not impossible since the center is 8' tall.

[chris_g]

Just a thought: If you want to minimize the blockage by the gable, it is best to make the rails in the South to North direction. That should eliminate the gable on the East side that you would otherwise have. Nobody does it that way AFAICT but why not - the rails are shorter that way, too. To not have a gable on the warm room side you could make that roof section single panel slanted, going up from East to West. When you close the roof that slant will look a bit odd, but it will give you the maximum clearance. Or you can make it a flat roof, but then you have to worry about sagging and water runoff issues.

Let me clarify my last post, here's what I had in mind. The observatory room is 10 x 13 x 5.5, warm room is 10 x 5 with a 5.5 foot East wall and an 8 foot West wall. The mount is offset 0.5 foot South of the North-South center. The 2 mounts have 5' center distance. The mount can easily be parked.

The roof slides off to the North. That way you can have a gable roof with no blockage issues because the roof sections are all slanted at 30 degrees.

chrisOpen1.png


chrisOpen2.png


I have a 5.5' lower wall and 7' higher wall myself; it does not give me a cramped feeling when setting things up. If the goal is to give a tour, that will be harder but not impossible since the center is 8' tall.

I like the 30-degree pitch roof, would make things easier to line up initially as well, my only concern with that would be possible water leakage between the two rooms. Something to discuss with a builder, thank you for that!

[chris_g]

I have a 5.5' lower wall and 7' higher wall myself; it does not give me a cramped feeling when setting things up. If the goal is to give a tour, that will be harder but not impossible since the center is 8' tall.

Question, I've seen the lower southern wall design for a Dob, would I need something like that as I have no plans to add one? And why go less than 30 degrees unless for visual, something I would set up on the outside pad if I were to ever do that.

[chris_g]

Gotta love triangles, isosceles triangle tells me how tall the roof is base=5.5 feet, a=3.175 = Base angle = 29.987, height = 2.75' Obsy northern wall effectively 8.25', Distance to wall = 5.875 with roof open

Rt triangle tells me h=8.25, b=5.875, hypotenuse angle = 54.54, mount height minimum at this placement is 42" to achieve a 30-degree horizon.

Who would have thought I would have ever used geometry when I was in school, we all had a laugh! Now I have a basic roof design I can put to this as well. I can now also determine optimum placement based on gable roof design at 30 degree pitch But now you have wind issues with a wall that low. It is though the same height as the observation tent when the roof is off, interesting.

Redesign coming with new skills and knowledge about roof design.

I'll have a new minimalist two mount design with gable roof taken into account.

Thank you!

[chris_g]

A quick run through of the triangle math confirms that a gable roof at 30 degree pitch rolling to the north, mount height approximately 42" placed n the current building design. I keep my 7-foot walls. Now the only question is, do I need a fold down southern wall?

[chris_g]

Hey @JayTee ! I spent my day in Geometry!

[SkyHiker]

I have a 5.5' lower wall and 7' higher wall myself; it does not give me a cramped feeling when setting things up. If the goal is to give a tour, that will be harder but not impossible since the center is 8' tall.

Question, I've seen the lower southern wall design for a Dob, would I need something like that as I have no plans to add one? And why go less than 30 degrees unless for visual, something I would set up on the outside pad if I were to ever do that.

I would not go lower than 5.5' because you need wind shielding, and your observatory is wider and more open than my little one (that also has slanted walls and a house wall on one side). It may be safer to go 6' or 6.5' because you can always raise the mount.

The most constricting part is actually the tripod so the taller, the wider and the more constriction. You leave two 3x3' sections that you can dig out in case you later decide to put piers in, right? That would give you room to move around easily.

Of course if you are using a contractor, would it not be more efficient to have them pour 2 pier bases with rebar sticking up while they're at it, so you can pour concrete piers on them? In that case don't forget to put tubes for power and communication lines on before they pour the pad, that's something you can't do after the fact.

[Graeme1858]

Just a thought: If you want to minimize the blockage by the gable.....

My roof rolls off parallel to the gable ends for the same reason. The roof slope is 20º so the blockage is zero as it matches the lowest angle the telescope can go as a function of wall height. I haven't got a warm room but I have got an off centre pier and a desk one end. The roof rolls off the pier end so the movement is 3m, full length. In retrospect, the other way, over the desk end would have shortened the roll off movement, but it's not a show stopper at all.

Good thread Chris!

Graeme

[chris_g]

Of course if you are using a contractor, would it not be more efficient to have them pour 2 pier bases with rebar sticking up while they're at it, so you can pour concrete piers on them? In that case don't forget to put tubes for power and communication lines on before they pour the pad, that's something you can't do after the fact.

Conduit for power and comms will be buried prior to pouring the pad, pier or no pier.

I'm looking at the pics @Gordon posted in Rimrock, https://theskysearchers.com/viewtopic.p ... 82#p203282.

A pier base, a 3x3 concrete pad with a hole in the middle of it for a pedestal. It looks simple enough. How deep does the hole go? I remember reading threads about perma frost, water tables and such. Using a pier though loses the flexibility of a variable height tripod. I did measure from the base of the EQ6's tripod at full height, 58"x58', 36"x36" at its lowest. The AZ-EQ5 is also 36" at its lowest. Don't know what its widest is though.

In keeping things simple and initial construction costs down, could I not bolt a pier to the pad at a later date? https://optcorp.com/collections/telesco ... crete-base or https://optcorp.com/collections/telesco ... er-42-inch. This one has that magic number of 42" height.

[chris_g]

Good thread Chris!

Thank you. Once the design is finished, I am going to try and write something up to the effect of, "How to design your own Observatory for Dummies" only using two special triangles.