In this video, we’ll explore why distances in astronomy are so important and how we measure them. Distances to stars are crucial because they allow us to determine other essential properties like physical size, luminosity, mass, and true motion through space. However, measuring these distances is challenging since we can’t physically go to the stars or use traditional measuring tools. Instead, we rely on geometry, particularly trigonometry and triangulation, to determine stellar distances. One common method is parallax, which involves measuring the apparent shift of a star against the background of more distant stars as Earth orbits the Sun. This shift is small, usually less than an arcsecond, and requires precise instruments to measure. The first parallax measurement was achieved in 1837 for the star 61 Cygni. For example, Proxima Centauri, the closest star to the Sun, has a parallax of about 0.77 arcseconds, equivalent to a distance of 1.3 parsecs. A parsec, or “parallax of one arcsecond,” is an astronomical unit of distance equal to about 3.26 light years or roughly 30 trillion kilometers. Measuring distances starts with determining the distance to the Sun, which we achieve by triangulating using Venus’ position in its orbit. By knowing the distance from Venus to the Sun and measuring the angle between Venus and the Sun as seen from Earth, we can calculate the distance to the Sun. Modern missions like the European Space Agency’s Hipparcos and Gaia have vastly improved our ability to measure stellar parallax, giving us data on millions of stars and extending our reach further into the Milky Way. Understanding these distances is fundamental to our knowledge of the cosmos, starting from local stars to the far reaches of the galaxy.
ESA's Hipparcos Mission: https://www.cosmos.esa.int/web/hipparcos
ESA's Gaia Mission: http://sci.esa.int/gaia/