Astronomy Names

For many of us, the names of stars, planets and moons are familiar. But how are these names chosen and what rules do we follow? Astronomy names are based on a variety of factors including the location of the star, its colour and brightness, and historical associations with mythology. As the International Astronomical Union (IAU) continues to delve into the rich diversity of worldwide history and culture, its Working Group on Stellar Nomenclature (WGSN) is debating how we might name future objects, including new stars.

Historically, astronomers used constellations as units of measurement and constellation names to identify individual stars. The most prominent constellations are the Big Dipper, Orion, and Canis Major. Many of the stars in these constellations were named by ancient astrologers, either from Greek or Latin sources. The star Regulus in the constellation Leo is one example. It is also known as the ‘little king’ or ‘prince of the north’, a name that appears in Persian astronomy books from the 16th century. The brightest star in the constellation is Sirius, which is named after the dog god.

Some astronomical names have been preserved almost unchanged for millennia, including those of the Pleiades open star cluster. These are named after members of a family in Greek mythology, as in Asterope and Perseus, or members of the Orion family (Canopus, Sirius, Alcyone). Other names have been modified by modern astronomers for clarity. For instance, the star Betelgeuse was originally called rktouros ‘the bear’. It is now more easily identified as a blue-white giant.

The Arabic word ‘al’ begins numerous star names, as in aldebaran and algenib. The Greek definite article ‘the’ is omitted from most constellation names, although it can be added to some, such as Canis Major. Some star names have a Latin suffix such as ‘eta’ or ‘delta’ to distinguish them from other stars in the same constellation, for example alpha Centauri and delta Scuti. Others are pronounced as written, such as Aldebaran and Betelgeuse.

In 1862, a cataloguer named Friedrich Wilhelm Argelander proposed a scheme for classifying variable stars, whose brightness fluctuates over time. Building on Bayer’s system, this allowed a letter R through Z to be assigned to the brightest star in each constellation. In this way, he distinguished variable stars from those that are constant in brightness.

Variable stars are given names based on their apparent colour and brightness, as well as on the fact that they appear to move around in the sky over long periods of time. This system, based on the letters of the alphabet, has been used to label a large number of stars since then.

In addition to this naming scheme, the IAU has established guidelines for the use of names for natural satellites of planets. These are largely drawn from a rich tradition of mythological characters, and also take into account the relative sizes of the planets and their satellites. For example, a binary transneptunian satellite that is similar in size to Pluto will receive a name derived from the mythological underworld gods.