Global speedometer.

[Sean-Roach]

I figured out how to clock the orbital velocity of the sun and had to put it somewhere where it was visible. (Side of a building in red spraypaint didn't seem to be as good of an option.)

Okay, given that the speed of light is a true constant, that it isn't effected by the velocity of its source. Meaning that if you shine a flashlight from the front of a moving vehicle, the light from it isn't traveling 55-65 MPH faster than light shone from a flashlight standing still.

Given that if you're on a platform moving forward at rate X, and you move sideways at rate Y, from a stationary point, you appear to be moving at sqrt(XXYY), and thus, from your perspective light shone from a flashlight would appear to be going slower if you were moving side to side, as the side to side motion compounds the effect of the forward velocity to some degree.

If you placed a device, running east-west at the equator, that measured the speed of a reflected beam of light, the surface velocity of the earth would be negated by the reflection. If the surface velocity of the earth is n, and the observed speed of light is listed as m, using c for the actual speed of light, (simplifying certainly, and borrowing from history. Then since the sun goes east-west, the earth is moving west-east. Then the beam going east-west would go at an observed rate of c-n, while the reflected beam, going west-east would appear to travel at c+n, thus the sum of the two (c-n)+(c+n), would yield actual c.

Except the orbital velocity of the earth comes into play.

As a sidereal day is shorter than a solar day, the earth is rotating in a manner consistant with its revolution, as if it were a large wheel rolling around a disk that is it's orbit. This means that the surface velocity of the earth is greatest at midnight, and would appear to stand still, in relation to the sun, at noon, if the circumference of the earth multiplied by the number of days in a year actually matched the circumference of the earths orbit. I'm assuming it doesn't, which means the earths surface does not appear to stop in relation to it's orbit at noon.

At noon, if 365*the circumference of the earth <= the circumference of the earth's orbit, the surface of the earth at that point is moving at its slowest rate.

At this point, if the sun were standing still itself, a measure of the speed of light would result in the fastest numbers, (although some the remaining motion in line with the earths orbit would still have an effect.)

All these speeds, with the exception of the speed of light itself, can be observed without considering the speed of light. We know the lenght of a year, and we know the radius of the earths orbit, thus we know the orbital velocity of the earth as observed from a stationary point in relation to the solar system. We know the radius of the earth, and we know the length of a day, thus we know the surface velocity of any point on the earth, as observed from a point that is stationary to the earths center.

By noting the effects of the suns own orbital velocity on the observed speed of light after either eliminating the effects of the other velocities, either by choosing the time of the experiment carefully, or by sending light through mirrors that allow the reflection to balance them, (such as sending the light East, bouncing it back West, and measuring it at the point of origin to eliminate East West velocity from being a factor, in this case, you have to take into account the X, Y, and Z axis, gravity would also be a factor, but would have to be calculated out, unless anyone would like to do this trick in microgravity,) you should be able to note the remaining effects on the observed speed of light. By noting when in the day light goes "faster" and when it goes "slower, you should be able to determine when the earth is moving slower or faster in relation to a true zero velocity respectively. By noting which of the three beams, (X, Y, and Z), is fastest, you can determine direction, and by noting the difference, and thus the fractional effect on the observed speed of light, you can determine velocity.

Sort of like measuring the forward speed of a gear from the pen on a spyrograph.

By the way, if a sidereal day were one year, the earth would always show one face to the sun, just as the moon shows the earth the same face from day to day to year to year.