If we ascertain the parallactic motion of a group of stars, then we can find their average distance.
The most obvious and direct method is to determine the parallactic motion of the stars of known parallax.
The parallactic shift of the nearest of the stars as seen from opposite sides of the earth's orbit, is many times smaller.
How shall we adequately describe the extreme minuteness of the parallactic ellipses in the case of even the nearest stars?
From the parallactic motion of the star it is possible to deduce its distance from the sun, or its parallax.
This was formerly called the angle of position, and is also termed the parallactic angle (which see).
There is, however, a still graver and quite insuperable distinction between the parallactic path and the aberrational path.
If a penny-piece were placed on this sphere, in front of each of the stars, every parallactic ellipse would be totally concealed.
parallax par·al·lax (pār'ə-lāks')
The apparent displacement of an object caused by a change in the position from which it is viewed.
An apparent shift in the position of an object, such as a star, caused by a change in the observer's position that provides a new line of sight. The parallax of nearby stars caused by observing them from opposite points in Earth's orbit around the Sun is used in estimating the stars' distance from Earth through triangulation.