How long is the baseline in measuring stellar parallax?

Question

How long is the baseline in measuring stellar parallax?

Answer 1

Two times the sun earth average distance.That is 300million kilometers.

Answer 2

Typically, you take a measurement, wait nearly 6 months, take another, and 6 months after that, you take another.  You don't want to measure proper motion, you want to measure distance.  So you have to subtract out proper motion.  But, it's usually near 2 AU, or about 180 million miles.

The right way to do this, in my opinion, is send out two space craft, and take simultaneous measurements. Then you don't have to guess what the proper motion is. The baseline is the distance between the two space craft measured perpendicular to the direction of the star you want to measure.  But since at least one of the space craft is not near the Earth, the distance can be anything.  And the bigger the better.

Measurements of parallax have been made by the hipparcos satellite, and by the Hubble Space Telescope's fine guidance censors.  Hipparcos had the feature that it got the distances to many stars, and the integrated solutions take all that into account.  The HST has the feature that the mirror is bigger, which gives the individual measurements better accuracy.  But the numbers differ, and each group claims superiority.  Really, we need two scopes.

Answer 3

Stellar would be about 180 Million Miles.

Distance measurement by parallax is a special case of the principle of triangulation, which states that one can solve for all the sides and angles in a network of triangles if, in addition to all the angles in the network, the length of at least one side has been measured. Thus, the careful measurement of the length of one baseline can fix the scale of an entire triangulation network. In parallax, the triangle is extremely long and narrow, and by measuring both its shortest side (the motion of the observer) and the small top angle (always less than 1 arcsecond,[3] leaving the other two close to 90 degrees), the length of the long sides (in practice considered to be equal) can be determined.

Assuming the angle is small (see derivation below), the distance to an object (measured in parsecs) is the reciprocal of the parallax (measured in arcseconds): d(pc) = 1 / p(arcsec). For example, the distance to Proxima Centauri is 1/0.772=1.29 parsecs (4.2 ly).