And the speed of light is a constant in any reference frame. (NOT). In 1913 Sagnac used interferometry like Michelson but on a rotating platform, trying to detect the rotation of the earth. What his results showed was that when light emitted in opposite directions on a platform in motion, it does NOT travel at the same speed.
This is what is known as the Sagnac Effect
. This of course is common sense Newtonian mechanics. Isn't it odd that what is common sense intuition had to be given the title of an "effect" after Einstein's Special Relativity theory had taken hold? According to Einstein light must travel at the same speed, c, regardless of reference frame. GPS is a rotating real-life example of the Sagnac experiment. What does it say, Relativity or not? GPS, I understand, comes down on the side of Sagnac, and has built in corrections, essentially v+c, and v-c, simple Euclidean vector geometry. I think when relativists claim the Sagnac Effect proves relativity, I have read explanations that seems to delve into time synchronization in multiple reference frames. This I believe is going down the same path as the Twin Paradox argument. This is a "relatively" simple thought experiment, which should have, in a sane world, immediately debunked Relativity, as explained in M. Bowden's link below at 2m. They also talk about light moving in "spiral" path, causing this effect, since the satellites are in orbit. Sorry, not buying that one. The Sagnac Effect proves the existence of the ether, the absolute reference frame of the universe. Special Relativity completely throws out the ether, but General Relativity kind of brings it back as the space-time continuum, in a veiled contradiction(Ref: The Journey Movie). Now, you may have heard of the quantum void, or zero point energy. In order to do good science, Quantum mechanics had to sneak back the ether by another name, due to the elevation of Einstein to cult status in physics.
Here is a good web site on the Sagnac Effect
Also the Relativity Fraud by M Bowden
covers how the Sagnac Effect debunks Relativity at 14m, along with many other experiments, and shows comments of renowned scientists of Einstein's time, about how science had departed from its search for the truth by adopting Relativity.
In the JTTCOTU movie, a nice animated graphic shows that the corrections to the GPS systems are directly attributable to the Sagnac Effect with the emitted and returned waves being depicted at different speeds. Here is a snapshot. It shows communication between 2 satellites, while talking about an adjustment that must occur between the satellite and a ground receiver, since we are talking about the difference between emitters based on the E-W rotation of the Earth. This appears to be a slight error in the movie. For that end I have made a correction to the snapped graphic from the movie with the red and white arrows to a ground receiver.
Michelson-Gale was conducted in 1925 and will be evaluated next.