Yes, they have outside venues to explore to balance it out just in case you get too cold
Depending how busy it is, the more bodies, the warmer it is. For me it was comfortable when it wasn't busy. There are outdoor areas too at the science center. If you plan on sitting through an IMAX movie or go to the planetarium, I suggest a light jacket. If not, you'll be walking around getting warm that way.
Not particularly. Maybe a light jacket would be nice, but if you are going on a hot day over the summer, it will just feel nice and air conditioned.
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