3 ms·
They don't have to be visible to the human eyes, just visible to instruments. With band filters and a narrow field of view you can get a stronger signal that st
by the8472 8y ago
They don't have to be visible to the human eyes, just visible to instruments. With band filters and a narrow field of view you can get a stronger signal that sticks out from the the approximately uniform sky background. I mean the altitude helps, but it's not necessary.