Trigonometric parallax is a method of determining the distances by using triangulation together with parallax. The method is used by surveyors to determine terrestrial distances, and is used by astronomers to determine distances to certain nearby stars.
Using trigonometry in astronomy has allowed us to calculate the distance to nearby stars through parallax. Parallax is, “The effect whereby the position or direction of an object appears to differ when viewed from different positions.” The movement of the star against the background as we orbit the Sun is called its parallax. As we all understand the earth orbits around the sun once a year, thus creating a six month interval in which the earth is looking at a star from the two corners of an isosceles triangle (where the point is at the star). We can observe how far the star appears against the back of galaxies in that time and find the angle of the triangle from that. With the angle and the length of the base (the diameter of the Earth’s orbit) we can find the height of the triangle – or the distance to the star.
“Over 4 years from 1989 to 1993, the Hipparcos Space Astrometry Mission measured the trigonometric parallax of nearly 120,000 stars with an accuracy of 0.002 arcsec. The GAIA mission, to be launched in 2010, will be able to measure parallaxes to an accuracy of 10-6 arcsec, allowing distances to be determined for more than 200 million stars.”
If the parallax angle, p, is measured in arcseconds (arcsec), then the distance to the star, d in parsecs (pc) is given by:
TRIGONOMETRY IN THE "REAL WORLD" 