Re: [Phys-l] celestial motion

[Brian Whatcott <betwys1@sbcglobal.net>]

At 09:24 AM 8/22/2008, Anthony  Lapinski, you wrote:
> ///
> What I want to know is the Sun's angular speed in the sky. The Sun is
> about 0.5° across. So in a 12-hour day, it moves 180° from east to west.
> This is 15°/hr, or 0.25°/min. When we look at a sunset, it already
> happened. Since light takes about 8 min to go from the Sun to Earth, the
> Sun has moved 2° in this time -- about 4 solar diameters.! This seems a
> bit large, or did I make an error?


Hmmm...the event I think you have in mind for Sunset is the time of last
light visible from the Sun. This is signalling an obscuration happening
a little further than your local horizon (the last light bends near
the Earth's surface, no doubt.)
 You could argue then that the event in question is transmitted to you
 with a delay corresponding to the speed of light traveling
 10, 15, 20 miles from your horizon to you?



Brian Whatcott    Altus OK    Eureka!