Time for some history and astronomy lessons ...(NOTE: The sun is a star)
Starlight and Rain
The next substantial improvement in measuring the speed of light took place in 1728, in England. An astronomer James Bradley, sailing on the Thames with some friends, noticed that the little pennant on top of the mast changed position each time the boat put about, even though the wind was steady. He thought of the boat as the earth in orbit, the wind as starlight coming from some distant star, and reasoned that the apparent direction the starlight was blowing in would depend on the way the earth was moving.
Another possible analogy is to imagine the starlight as a steady downpour of rain on a windless day, and to think of yourself as walking around a circular path at a steady pace. The apparent direction of the incoming rain will not be vertically downwardsmore will hit your front than your back. In fact, if the rain is falling at, say, 15 mph, and you are walking at 3 mph, to you as observer the rain will be coming down at a slant so that it has a vertical speed of 15 mph, and a horizontal speed towards you of 3 mph. Whether it is slanting down from the north or east or whatever at any given time depends on where you are on the circular path at that moment. Bradley reasoned that the apparent direction of incoming starlight must vary in just this way, but the angular change would be a lot less dramatic. The earths speed in orbit is about 18 miles per second, he knew from Römers work that light went at about 10,000 times that speed. That meant that the angular variation in apparent incoming direction of starlight was about the magnitude of the small angle in a right-angled triangle with one side 10,000 times longer than the other, about one two-hundredth of a degree.
Notice this would have been just at the limits of Tychos measurements, but the advent of the telescope, and general improvements in engineering, meant this small angle was quite accurately measurable by Bradleys time, and he found the velocity of light to be 185,000 miles per second, with an accuracy of about one percent.
Time for some history and astronomy lessons ...(NOTE: The sun is a star)Yes, Light-time correction and the Aberration of light.
Starlight and Rain [excerpt]