The Fred Lawrence Whipple Observatory (FLWO) is the largest field installation of the Smithsonian Astrophysical Observatory (SAO) outside Cambridge, MA. Since October 1968, the FLWO has been used as the site for experiments requiring extremely dark skies, dry climate, and good "optical seeing."
The Whipple Observatory Visitor Center is less than an hour drive south of Tucson. Take a picnic lunch. It is bound to be cooler in the summer as well, especially if you take the tour at the top.
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