The distance of nearby stars is measured using a method based on the parallax. In this method, the angle subtended by a star at a given location at two different time points is measured. Since the Earth orbits around the Sun, the given star will form different angle at different time points. This apparent motion with respect to more distant stars is known as stellar parallax. The inverse of this angle, measured in arcseonds, is the distance of star in parsecs. For example, the nearest star (other than Sun), Proxima Centauri has a parallax of 0.772 arcseonds and thus, a distance of about 1.3 parsecs.
This method is only applicable for stars which are relatively closer to Earth and provide a measurable stellar parallax. Even with a dedicated satellite in space, we are limited to about 10,000 parsecs or so. Therefore, we can only use this method after obtaining a measurable stellar parallax.
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