Question

What is stellar parallax caused by?

Answer 1

It is apparent angular displacement of a star caused by our day-by-day displacement, in the Earth's orbit.

Explanation:

Apparently, the star configuration is stationary, in a short interval of 24 hours. Actually, the star turns `relative` to the observer, through `360^o`, as we make one round along the Earth's orbit.

Due to the observer's displacement, there is apparent displacement of the star. This angular displacement (spacing) is called stellar parallax.

Stellar parallax is used to approximate a star's distance in AU or, in larger unit of distance, light year (ly)..