Sep 02

September 2006 / Extra

Whats Up in the Sky September, 2006 (Extra)

How Celestial Objects Are Named

Amid all the Pluto is no longer a planet hubbub, some friends recently asked me about how things like planets and stars get named. After a brief explanation with a couple of examples, I became intrigued by some of the more subtle details in this story.

The Sun, Moon, and visible planets (Mercury, Venus, Mars, Jupiter and Saturn) were all named by the ancients who believed them to be mythological gods. The astronomers who first identified Uranus, Neptune, and Pluto continued that tradition. Constellations such as Hercules, Perseus, and Andromeda also take their names from ancient mythology, although several visible only in the southern hemisphere have names like Antila (the Air Pump) and Telescopium because they were named by European explorers who first sailed southern seas.

Other categories of objects follow different rules of naming. Satellites of planets go through a process where they first receive a number indicating the year of discovery, then are assigned a Roman numeral, and then may receive a name from mythology. So when Voyager 2 found a bunch of new moons around Neptune in 1989 they were first designated, for example, S/1989 N 1 which later became Neptune VIII and finally Proteus. The moons of Uranus are the exception to the mythology rule – they are named by their discoverers after characters from the writings of Shakespeare and Pope such as Caliban and Puck.

Asteroids are also given a provisional number at first, but when their orbits are understood well enough for us to be able to predict their positions, they receive a permanent number and name. Therefore, 253 Mathilde is the 253rd asteroid to be numbered but not necessarily the 253rd to be discovered. Asteroid discoverers are afforded much more latitude in their choice of names. Asteroids can be named for almost anything so we have 2309 Mr. Spock, 3834 Zappafrank and 8749 Beatles.

Comets are generally named for the person or persons (up to three) who first discover them. Comet Halley is probably the most familiar example, named after famed English scientist and astronomer Edmund Halley. He was not the first to observe the comet, records of its appearance date back to ancient China, but he was the first to understand its nature and predict its return. More recent examples include comets Hale-Bopp, Hyakutake and Shoemaker-Levy 9 (the 9th one found by Carolyn and Gene Shoemaker and David Levy).

Surface features like craters or mountains on asteroids, planets, or moons follow complicated rules set by the International Astronomical Union Nomenclature Committee. Basically they are named after noteworthy places, things, or individuals who are no longer be living nor political or religious figures from the last 200 years. Examples include lunar craters Tycho, Copernicus, and Scobee; valleys on Mercury such as Arecibo and Goldstone (named after radio telescopes); and the Amsterdam crater on Mars. These features also take their names from the places and stories of Norse, Chinese, Japanese, Indian, Hawaiian, Native American and Aboriginal mythology.

There is one group of objects that no longer receive names other than catalogue numbers: the stars. The brightest stars, like Sirius or Betelgeuse, retain their names from antiquity, but astronomers use several systems for naming stars so Sirius is also known as Alpha Canis Majoris, 9 Canis Majoris, HR 2491, HD 48915, BD-16 1591 and the Dog Star. Stars, however, cannot be officially named after you, nor can you buy a star. Those names exist only in the book the company sells you.

Its all in the name and its all up in the sky.

Peter Burkey – SAAA President