The mathematical value of the speed of light, c was first discovered as being very large, but finite, by Danish astronomer Olaf Roemer in 1676. During his astronomical observations of Jupiter and the eclipses of its many moons, he calculated the speed of light to a very close approximation. The light covered across the vast distance to the Earth, L, as the moon ventured in and out of Jupiter‘s shadow, at various points of the yearly seasons as both planets orbited the Sun. He was able to compare the times, t, from several observations of Jupiter’s eclipses to arrive at c.

In 1879, Scottish physicist James Clerk Maxwell proposed, in a letter to American astronomer David Peck Todd, to extend Roemer’s experiments to find the speed, v, of the Earth-Jupiter tandem as the Solar System celestially circumnavigated through the Aether of deep space. At certain times of its yearly orbit, the Earth is in a very advantageous position to observe the moons, such as Io, of Jupiter pass through its shadow, created by the Sun. When Io emerges from this shadow, or eclipse, this event is observable on the Earth.

If the E-J tandem were at rest in space/Aether, then the light would experience a delay of t = L / c over and above the time for Io to make a single orbit of Jupiter, from shadow to shadow. This is the difference as determined by comparing the orbit times between two or more eclipses. At various points of the year this delay, L / c, is longer or shorter, because, as speculated by Roemer, the distance, L, between Earth and Jupiter is changing. By some mathematical acrobatics, Roemer was able to isolate c, and solve for its value.

So Maxwell speculated that there was an unaccounted component due to the Solar System’s (with the Earth and Jupiter in it) velocity through interstellar space. To find this velocity, v, became his goal. By making his astronomical observations when Jupiter takes their least amount of time (shortest, L, or L - vt₂) between eclipses of Io, and then waiting until the eclipses take their greatest time (longest, L, or L + vt₁) for an orbit, then Maxwell concluded that he could introduce the velocity, v of the Solar System.

These two formed a tandem in which their distance apart, L, was aligned with the hypothetical motion of the SS through space. From this, Maxwell thought that based on astronomical observations at these opposite extremes, the delays would be different. The light is traveling alternately, with and against the motion of the SS. Then he supposed that he could introduce L / (c + v) and L / (c - v); then add these values (I have chosen to add rather than subtract, [2Lc] / [c² - v²], from Michelson-Morley) to solve for the velocity of the SS (and E-J tandem), v.

According to Einstein’s STR the delay due to the motion of the planets vanishes in the warping of space-time formulas. But astronomical observations have not made a statement confirming or denying the existence of this small delay which could be due to the velocity of the Solar System.

http://en.wikipedia.org/wiki/Ole_R%C3%B8mer

http://ether.wikiext.org/wiki/Maxwell_1879_en