What is the best method to increase the accuracy of the parallax measurement of star distances? keep a record of the observations and do not repeat them

take observations simultaneously with different instruments

keep a gap of about six months between two observations

take observations from two points which are very close to each other

C.

Explanation:

Parallax method is used to measure the distance of nearby objects in space or measurement of star distances. Parallax method uses the measurement of  movement of star's against starts at far points as Earth revolves around the sun.

To improve the accurate measurement of star distances through parallax method, a gap of about six months between two observations.

In the parallax measurement, two angles are measured and it includes Earth on one side of its orbit, Earth six months later on the other side of its orbit and side of a triangle formed by the star. This six month gap ensures that measurement of stars is taken from two farthest points which gives a large arc length.

As parallax is based on geometry so, it ensure that the large arc length will reduce the error in the measurement of the angle and the distance will be accurate.

Hence, the correct answer is  C.