Mystery Bug

I found this bug on the outside wall of a store in Northampton, Ma. It was still alive, and didn't seem afraid of me -- I got about 1" from it. It was about 4-5" long. Does anyone know what type of bug this is? I would not have been surprised to find this bug back home in Thailand... or the Amazon... but W.Mass? This thing's a monster! What *is* it?

**update Found! it's a male dobsonfly