My friend asked me this weekend if her Meade LX90 would be okay if left in the car with this extreme heat. I told her that for most astronomical scopes, it poses no problem unless the objectives/mirrors are exposed to the direct sunlight, in which case some of the cements in the lenses may gum up or loosen. As long as the scope was covered, should be no problem for a day or so.
On the other hand, I never recommend leaving a binocular or spotting scope in a vehicle for extended periods of time, though I know many customers that do. The problem in any sealed optical system (as opposed to an unsealed astronomical scope) is the extreme change in temperature as a vehicle heats up by day and cools back down at night. This is very hard on the seals - lots of expanding and contracting. Sooner or later, this causes the scope or bino to fog up or leak. I've even seen this in "waterproof" models.
Of course, leaving any valuable in a vehicle also invites a break in. I know this firsthand.
