Measurement.

Triangulation is a common method applied in measuring optical distances. It employs the technique of trigonometry to determine an unknown distance to an object using two other locations with a known distance between them as reference points. Space objects can be observed from two different positions on the surface of the earth which makes this method very applicable in calculating their relative distances from the Earth. The most important factors are the linear distance between the two positions of observance and the angle subtended by the object to the line of observance due to the apparent shift in position (Seeds, Backman, 2009). The ground measurements are used to draw a triangular scale model and thereafter use it to determine the unknown distance. Objects that are at a far distance from the observer tend to subtend smaller angles from the line of observance.

Parsec is a combination of two words namely parallax and second.  It refers to the distance an astronomical object would be if it had a parallax of exactly one second of an arc. In the other hand, light-year is the distance light travels in a year. This is equivalent to 6 billion miles. One parsec is equivalent to 3.258 light years.

Proper motion refers to a noticeable change of position of an astronomical object on a celestial sphere. Proper motion is always represented by a symbol . This velocity is generally quoted in units of seconds of arc per year. Space objects especially stars have small proper motions. In comparison to other stars, Barnards Star is the only star known to have the largest proper motion (Seeds, Backman, 2009). It is known to move at a rate of 10.3 seconds of arc every year in comparison to Moon which has a velocity