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The telescope big bear is located in the Southern California. According to the wikipedia page, water can cool the observatory.

Is it better to build it on a cold high mountain with stable and clear atmosphere?

What is the difference when building a solar and an optical telescope? Optical telescopes are usually not build on lakes.

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    $\begingroup$ I think if you re-read that article, you'll find that you've misunderstood it, and it actually answers your question. The lake cools the nearby atmosphere. $\endgroup$
    – andy256
    May 25 '15 at 3:52
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To amplify andy256's comment, the problem that solar telescopes face is that heating of the surrounding ground during the day gives rise to turbulence in the air near the ground, making the observing conditions worse (think of the heat shimmer just above the surface of hot pavement or a hot road -- that's turbulence bad enough for your naked eyes to notice). Since water has a high thermal inertia, it doesn't heat up as much as land does, so you get less turbulence. (Another approach is to put the telescope on top of a tower, above the worst of the turbulence.)

Note that Big Bear is at an altitude of 2,000 meters, so it is at a moderately high altitude.

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  • $\begingroup$ Because solar telescopes work at daytime, so they need more stable atmosphere. Although optical telescopes need stable atmosphere too, they work at night. Big bear is not far away from LA. Why do not we consider lakes in Canada? $\endgroup$ Jun 5 '15 at 15:52
  • $\begingroup$ A slightly better way to put it might be that the atmosphere is more unstable during the day, but yes... I gather that Big Bear has two additional advantages: high altitude and good weather (clear skies); plus, it's far enough from L.A. that air pollution isn't really a problem. I'd guess that many lakes in Canada aren't at a high altitude and/or don't have good enough weather. $\endgroup$ Jun 5 '15 at 15:54

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