Even at light speed, the Big Dipper is a long way out
From Sept. 26, 2007:
My wife and I were on our back patio the other night enjoying the night sky. While looking at the Big Dipper, I started to wonder just how big is it? If you were to start at the end of the handle and proceed to each of the six remaining stars ending up on the top of the ladle, how long would it take?
Do you know what an asterism is? It is a distinctive pattern of stars that is not a constellation. The Big Dipper is an asterism and, of course, makes up the tail and the flank of the Great Bear.
And I didn’t know this before: Mizar, the middle star in the Dipper’s handle, is actually a package of six stars. They just look like one star to us because they’re so far away.
The British call the Big Dipper the Plow. The ancient Greeks called it the Wagon. Native Americans saw the bowl of the Dipper as a bear and the tail as three men chasing it.
As you might have guessed, I’m stalling here because I haven’t found a very good answer to this question. I did find out that the star at the very end of the handle is 210 light years from Earth. The star at the top, outside edge of the ladle is 105 light years away from us, and the two stars at the bottom of the ladle are 90 and 78 light years away.
Sorry, that’s the best I could do.
How did astrophysicists first determine the speed of light?
In 1676, a Danish astronomer named Olaus Roemer came up with a speed of light of 140,000 miles per second.
This is a bit complicated — meaning I don’t understand it very well — but he came up with the number while observing regular eclipses of some of Jupiter’s moons. The times between regular intervals decreased by about 3.5 minutes when the Earth was moving toward Jupiter and increased by the same amount when we were moving away from it.
So Roemer did the math, which is more than I could do, and came up with 140,000 miles per second, which was pretty darn close to the right answer of 186,282.397.