Advice on pier building spot.

[Centus]

Hi,

I've been considering a pier build for a while now, and have narrowed it down to either ground based pier or top of the roof of my house pier.

My question to you, which is better?

Roof based, will of course have the benefit of less obstructions, but there is the question of heat coming off the house (I have a flat cement roof so it shouldn't be a problem as far as adding a concrete base for the pier when I build the second story), I have read somewhere that the heat coming off the house can cause bad seeing.

Ground based will require some digging for foundation, but should be sturdy enough, so it only has the down side of having an obstructed view of the south side of the sky (the house is there).

Any ideas?

Thanks!

[Astrokev]

I would imagine that the roof could get very warm since you live in Israel. I think this would take a long time to cool in the evening and is likely to give very poor seeing. I would play safe and build on the ground.

Kev

[Centus]

Thanks Kev, that's what I was thinking... bummer though because of the southern side of the sky.

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[ollypenrice]

It would surely be a simple matter to try a tripod based mount in both locations to see if the heat really was a problem. Standard wisdom says that it is a problem, but a conflicting standard wisdom sees many very serious observatories use well-raised floors to get the scope above the 'ground seeing.' Raised systems are used at the six million dollar Observatoire des Baronnies near to my place and at Tivoli in Namibia. There is a lot of concrete under the Baronnies telescope because it has to support the massive scope itself. In a nutshell I'd just try it. If south is your main interest put the scope on the edge of the roof at the south, perhaps? Just don't fall off...

I use concrete observing pads and have measured only the most trivial differences in cool down as compared with off-concrete control thermometers.

Experiment beats speculation.

Olly

[Centus]

Thanks olly, I have to admit it did not occur to me

Getting my mount to the roof would not be trivial but it would definitely be easier than building a pier and then checking..

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