GregH said:
I guess, I just find it very hard to believe that anything could stay hidden for that long with all the eyes we've had looking up at the sky.
My point is that, compared to the amount of sky, we have very few eyes. Think about it - we
don't have the ability to track all the near-Earth asteroids. We don't have enough eyes to keep track of the things that could very likely kill us, much less find things we don't know are a threat.
Also, note that we have not had particularly good, or particularly many, telescopes for all 60 years. Heck, IR telescopy didn't even start (much less become good, or common) until the 1960s! For something like half of those 60 years, we were effectively blind as a bat.
As far as "paint it black", well it still has to communicate, so we should have heard some sporadic radio frequencies
Assuming that they use wide-angle radio broadcast, and assuming that they do need to communicate at interplanetary ranges. But tight-beam is far more efficient.
it would still give off a heat signature - unless they never fire a retro rocket
You're in orbit around the sun - you don't have to fire a rocket unless you want to
change your orbit. It isn't hard to miss infrequent events.
or have managed to find a way to completely mask any manner of energy use at all.
We don't have IR eyes just scanning the sky at random, you know, much less anything like complete coverage. Those telescopes are
expensive, and are busy looking at specific things. They'd have to be emitting above-expected heat while crossing the field of view of a handful of telescopes.
And the field of view of the majority of telescopes (IR or otherwise) is typically tiny. They are generally watching light from very small cones of space. Failing to cross those cones is not difficult.