Double Star Images

Aberration of Starlight

You have to tilt your telescope to catch the star light just as you have to tilt your umbrella to keep off wind-driven rain. It is a matter of relative velocity.

Actual experiments involve measurements of the change in the apparent positions of stars at different times of the year.

Apparent Star Positions

You have to tilt your telescope to catch the star light just as you have to tilt your umbrella to keep off wind-driven rain. It is a matter of relative velocity.

When a distant star is viewed from the Earth at different times of the year, its apparent position will change as a result of the Earth's velocity through space. This apparent ellipse of motion of the star is called the aberration of starlight. Measurements of the size of this ellipse offer one piece of evidence that the velocity of light is independent of observer motion. This effect is independent of the parallax which permits the determination of the distance of the closest stars by triangulation.