Continued...
•So the Keck telescope
collects roughly 4,000,000 times more light than your eye. All other things being equal, it can see
objects 4,000,000 times
fainter than your eye. But, all other things are NOT equal...
–CCD detector
are about 90% efficient; your eye is about 5% efficient. That is, CCDs are about 18 times more
sensitive than your
eye.
–Your eye cannot store or record the light. In other words, your eye can’t do a time exposure. The human eye is like a video
camera that can’t record,
taking “exposures” about 1/10th of a second long. (That’s why you don’t notice the flickering of a movie
screen, which shows 24 frames
per second.) So, if a CCD camera takes a 1-hour time exposure (3600 seconds), that’s about 36,000
times more than one “frame”
of human vision.
–So really, the Keck can see things that are 4,000,000 times 18 times 36,000 times fainter than the human eye. That’s
about 3 trillion times fainter!