Seeing The Past

From Slackerpedia Galactica

No matter where you look or what you look at, you see things as they appeared in the past. That's because light moves at a finite speed.

Saturn is at opposition when the Sun, the Earth and Saturn are lined up, and Saturn is on the same side of the Sun as the Earth. At that point, Saturn is about as close to the Earth as it gets. When Saturn is on the other side of the Sun from the Earth, and all three are lined up, Saturn is at conjunction. Saturn is about as far from the Earth as it gets. That's about twice the distance from the Earth to the Sun farther than it was at the closest point. That's about 16 minutes and 20 seconds farther, as the photon flies.

So, if you carefully measure the orbit of Titan around Saturn at opposition, and predict where Titan will be at conjunction, and then look through your telescope at conjunction, you'll be off by 16 minutes and 20 seconds, if you didn't take into account the speed of light. Alternately, you'll be blinded trying to look through the Sun at Saturn.

If you look at M31, the Andromeda Galaxy, you see it as it looked about two and a quarter million years ago. Now, a couple million years doesn't age a 13 billion year old galaxy all that much. But the galaxy does rotate once every 200 million years. So by the time light from this galaxy gets to you, it has rotated about 1 percent, or maybe four degrees.

Let's look at nearby things. Light moves about a foot in a billionth of a second - a nanosecond. So, when my girlfriend is six feet away from me, I don't see her as she is, rather, I see her as she was 6 nanoseconds ago. She was younger then. If she is 100 feet away, I see her as she was 100 nanoseconds ago. She was much younger then. Clearly, the further away she is, the more youthful is her appearance. When you get to be our age, youth is good.

Oh yeah. I understand that I look better from large distances too.

Cosmology is the study of the evolution of the Universe. Cosmetology is the study of hair styles and such. But here is clear proof that Cosmology and Cosmetology are related disciplines.