I was watching an old Stargate episode with big alien ships in orbit, and I thought 'in real life that would be spotted pretty quickly... um, wouldn't it?'
I'm not saying I'm on the search for alien ships (if they do exist I don't think they have any trouble staying a step ahead of us anyhow). It just made me wonder about how much of what is in the sky, even pretty close by, we are really aware of.
Maybe there should be some parameters on this. Suppose a standard Federation star ship were to yet again accidentally go back in time to our era, due to their continuing disregard for basic tachyon safety procedures. The Enterprise is supposed to measure about 600 x 400 x 200 meters, weighs 4.5 million metric tons, and seems to have a metallic hull. How long would it take us to spot that in low Earth orbit? How about if it was in a high orbit?