Quote:

---

-----The concrete is the same temp as the earth so does that really affect the seeing? I have carpet down as an insulator, plus the pad is in the shade so it is not absorbing the suns heat.

-----

---

Post Extras:

Quote:

---

Concrete has considerable thermal inertia and if it is unsealed, it can have a big impact on humidity in an observatory. And it is NEVER thermally-matched to the ground it is sitting on or in. All it takes is an evening with a thermal imaging camera to conclusively-prove that concrete should be avoided whenever alternatives exist.

In this picture you will note that at 5:48pm, just after sunset, the observatory is at 35F but the concrete pad is still at 50F. The surrounding ground (barren, rocky) is around 40F. The concrete pad finally stabilized with the ground around 1am.

---

Post Extras:

Quote:

---

I have a slab and considering a sub-floor for

1) standing
2) those times you drop an EP.

With a roll off roof, I've never encountered thermal problems from the slab. Maybe because it's shaded? YMMV.

---

Post Extras:

Quote:

---

Concrete has considerable thermal inertia and if it is unsealed, it can have a big impact on humidity in an observatory. And it is NEVER thermally-matched to the ground it is sitting on or in. All it takes is an evening with a thermal imaging camera to conclusively-prove that concrete should be avoided whenever alternatives exist.

In this picture you will note that at 5:48pm, just after sunset, the observatory is at 35F but the concrete pad is still at 50F. The surrounding ground (barren, rocky) is around 40F. The concrete pad finally stabilized with the ground around 1am.

---

Post Extras:

Quote:

---

Quote:

---

I have a slab and considering a sub-floor for

1) standing
2) those times you drop an EP.

With a roll off roof, I've never encountered thermal problems from the slab. Maybe because it's shaded? YMMV.

---

<<SNIP>>
One way to evaluate if there are big thermal problems is to compare seeing between, say, 10pm and 3am. If the 3am seeing is consistently better than your 10pm seeing then you are likely suffering from local seeing problems.

<<SNIP>>

I hope this helps.

---

Yes, Erik...as I'm a visual observer who doesn't need to rise early I can/do this every clear night. Whatever OBS thermal issues are present are overwhelmed by the MC scope's thermal issue.

it's just a short scoot over to another scope that cools rapidly.

I attached a low resolution pic of the scopes from the Security

Edited by Tom and Beth (12/13/12 01:25 PM)

Post Extras:

Quote:

---

Quote:

---

Concrete has considerable thermal inertia and if it is unsealed, it can have a big impact on humidity in an observatory. And it is NEVER thermally-matched to the ground it is sitting on or in. All it takes is an evening with a thermal imaging camera to conclusively-prove that concrete should be avoided whenever alternatives exist.

In this picture you will note that at 5:48pm, just after sunset, the observatory is at 35F but the concrete pad is still at 50F. The surrounding ground (barren, rocky) is around 40F. The concrete pad finally stabilized with the ground around 1am.

---

That pic is all fine & Dandy. But there is a couple of questions:
1: Where is that Observatory
2: Is that a professional or a backyard observatory?
3: How much concrete is involved with that structure?
4: How much of the concrete is exposed to the Sun light during the day?


For the record, I am not opposed to a wood deck.

I just re-read you post, You counter-dick yourself.
"And it is NEVER thermally-matched to the ground it is sitting on or in." The next paragraph you said.

"The concrete pad finally stabilized with the ground around 1am."

---

You are right. I could have phrased that a lot better than I did.

Answers to your questions:

1&2. That fully-robotic observatory is owned by the University of Hawaii and is called VYSOS-20. It has an uninsulated Ash dome and contains a 20" Planewave RC scope on an Astro-Physics 3600GTO mount. It is located at the Mauna Loa Weather Observatory, on the slopes of Mauna Loa on the Big Island of Hawaii. Its coordinates are 19.535948, -155.576140. It is a barren, volcanic, incredibly-dry place at 11,000'. It could be described as a professional observatory built with high-end, COTS amateur equipment.

3. There is an estimated three cubic yards of concrete involved in that observatory's pier and foundation/floor.

4. About 5% of the concrete is exposed to the Sun at any given time during the day.

The observatory's inside and outside temperatures are like two sine waves that are permanently out of phase with each other. The inside temps are always following after the outside temps. Because of the concrete mass, the local seeing is "bad" until about 1am, when it improves to "marginal." At about 3am, the local seeing improves to "acceptable." About one hour after sunrise, the outside temperature warms past the inside temperature and then the inside stays cooler until about sunset, when the outside temps once again cool past the inside temps.

One solution I have recommended to the university is to insulate the dome and install a remote-computer-controlled A/C unit. The plan would be to pre-cool the observatory interior to the predicted night-time temperature when night-time operations would commence. This will use a whole-lot more electricity (especially painful at $0.47/kWh) and still wouldn't give ideal local seeing but it would improve their local seeing considerably.

Local seeing is a cumulative issue. People who choose to believe that they can ignore one factor because it is "swamped by other factors" are overlooking the reality that all of the factors are cumulative. Every improvement that can be reasonably-made will give dividends.

I hope this helps.

Post Extras:

Quote:

---

Concrete has considerable thermal inertia and if it is unsealed, it can have a big impact on humidity in an observatory. And it is NEVER thermally-matched to the ground it is sitting on or in.

---

So much for THAT theory

Post Extras: