Stellar Parallax

If  the Earth were stationary, a given line  joining  point A on the Earth, a nearby star C and any given distant star would never vary. However, if  the Earth changed its position in space and moved  from A to B, this alignment would also change. Thus, in the background  of more distant stars, the hearby star would apwar to shift from C₁  to C₂  as the Earth moved  from A to B. This apparent shifting of nearby stars against the background of more distant ones has been observed, and the phenomenanis  called Stellar parallax. It is a periodic kind of a chahge. A given star first shifts one way and then the other, during the course of  one year, hence it must be due to the fact that the Earth is moving around the Sun.  

The change is small, less than a second of  an arc. It was only  in  1838  that Friedrich Bessel, a German astronomer, could measure the stellar parallax of  a  star. -1  he  nearest star, the Sun when viewed against distant stars appears to shift approximately  1" per day.