BRAINCAKEStellar Parallax
Stellar parallax is the apparent shift in the position of a nearby star against the background of much more distant stars, caused by the Earth's motion around the Sun.
The position of the star is measured, and then measured again six months later, when the Earth is on the opposite side of its orbit. The baseline between the two observations is 2 AU. The parallax angle p is half the angle through which the star appears to move, so it is the angle subtended at the star by a baseline of 1 AU (the Earth-Sun distance).
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All 24 lessons in Astrophysics and Cosmology · All OCR A-level Physics topics