When you are interested in physics you must read “Unbelievable“!
When light travels through space by means of a medium (ether) one can assume two possible ethers: absolute and dragged ether.
In 1727 Bradley conducted measurements on a star called y-Draconis. This star stands at an angle of 75 degrees in relation to the elliptic path of the earth around the sun. Bradley registered during his observations that the position of the star y-Draconis seems to change with the position of the earth in her orbit around the sun. The observed apparent different elevation of the star is dependent on the position of the earth in orbit around the sun. This change of elevation was called stellar aberration. The stellar aberration cannot be explained by the parallax; the change of angle caused by the orbit around the Sun. The distance of the star y-Draconis to the Sun is too great to show measurable parallax.
You might compare this phenomenon with rain falling on the front shield of a car. When the car stands still and rain is falling with an angle at the front shield, this angle will decrease when the car moves forward. The rain seems to hit the shield more from the front. This seems so for the driver, but it is only appearance. The rain, of course, keeps falling down from the sky at the same angle independently of the movement of the car. When the driver goes in reverse, the rain appears to fall accordingly more from above.
When the movement of the earth influences ether, through which light travels in all directions with the same speed, then the speed effect of the earth around the sun has to disappear. In other words the measured speed of light reaching the observer on Earth is, with dragged ether, always the same c. Even if the actual speed of the photon approaching the Earth was different.
This is very good comparable with sound effects. The speed effect of a jet is not found in the speed of the sound waves. Whether the jet flies with 200 or 800 miles/hour this speed cannot be observed in the speed of the sound waves registered by the observer.
The speed of the jet can only be deduced with the observed Doppler-effect of the sound and/or the apparent different position where the sound waves seem to originate (comparable with stellar aberration).
When a photon is emitted towards the Earth from an object moving with v to the Earth than the speed of the photon towards the Earth will be c+v as long as the photon is in the ether under influence of the object. When the photon reaches the ether under influence of Earth the speed effect will disappear; only the Doppler-effect and stellar aberration of the speed are observable.
With dragged ether all direct speed effects of the Earth moving towards and from the star cannot be measured directly. The relative speed of the earth compared to y-Draconis cannot, with dragged ether, be present anymore. This however does not mean that the speed of a photon coming towards the earth and moving in ether under influence of the star was not approaching the earth with a different speed than the speed of light.
Figure 1. The light from star y-Draconis reaching our solar system.
If the Earth was in orbit around the sun and air was the medium, the speed of the earth through the air, the medium, would be approx. 0.1 km per hour. This very low speed, compared to the speed of sound, cannot be measured as soon as the sound waves leave the “air” under influence of the earth.
So according to the analogy the speed of the photons from the star y-Draconis, with dragged ether, will always reach the earth with the speed of light c. The speed towards or from the star cannot be measured. The only effects that remain are the Doppler-effect and the stellar aberration. The observer cannot determine the speed of the plane by means of the speed of the sound waves. The only information left in the sound wave is the Doppler- effect and the aberration (apparent change of angle of the sound wave).
The movement of the earth in orbit around the sun cannot be obtained from the speed of light when there is dragged ether. On earth it is therefore not possible with dragged ether to measure the speed towards or from any star on the basis of the measured speed of light. The effects that can be measured will be the Doppler-effect and the stellar aberration.
So with the assumption of the existence of dragged ether, having the same effect on light as the air has on sound waves, the conclusion that no stellar aberration can be measured is not justified. When drawing the conclusion that stellar aberration cannot exist when there is dragged ether, one gives credit to characteristics of dragged ether contrary to the physical entities of vacuum. We will show without any doubt that when dragged ether exist stellar aberration has to occur exactly the way it is measured. The measured stellar aberration is in fact the very strong empirical evidence that dragged ether has to exist.
Next chapter: The stellar aberration of the star y-Draconis with ether