Question

How long is the baseline in measuring stellar parallax ?

Answer 1

Parallax is the measure of distance of the distant object from two separate points. Stellar parallax is how far the star is present by measuring from two points. Stellar parallax method is used to find how far the sun is present away from the earth. Not only planets, any planet, star distance can be measured through this method.

Complete answer:
(i) The distance at where the star is present is measured from two far away points on the earth. Considering the distance between these two points is long as possible. This following picture depicts this stellar parallax.

(ii) The p is the parallax angle. The picture shows the right angled triangle with a parallax angle p. The baseline is the distance between the two points where we measured the distance from the earth. Therefore the baseline is the length of $2AU$ . We know that the distance between the earth and sun is equal to $1AU$ . Now here the baseline is twice the astronomical unit(AU).
(iii) Therefore the length of the baseline is $2AU$.

Additional information:
(i) The measurement of the parallax can be measured from the earth is called a geo-centric parallax. The measurement of the parallax that can be measured from the sun is called a helio-centric parallax.
(ii) If the baseline and the direction of the distant object is known, the parallax angle can be found. So the distance between the two celestial bodies can be found.

Note: The stellar parallax is the difference between the distance of an object measured from two different points. The baseline is the diameter of the orbit of the earth. Therefore the baseline is measured as $2AU$. Using the baseline, direction of the object , the parallax angle and the distance between the two celestial bodies is known.