Naming Celestial Objects

See how the International Astronomical Union names newly discovered celestial objects.

By Jeffrey Kluger|Monday, June 01, 1992
Me, personally, I’ve never taken Io very seriously--and I don’t know how anybody could.

Io, as you know if you’re up on your cosmic census, is one of the largest of Jupiter’s 16 moons. It’s a perfectly respectable moon--one of the only moons with its own volcanoes--but it has one of the silliest names in the solar system. The first time I saw Io in print I thought it was either a typo or the international pictogram for Boris and Natasha. The first time I heard it pronounced (a nice, phonetic eye-oh), all I could think of was It’s off to work we go as sung by the Seven Cockney Dwarfs.

Now, of course, I know better. It was the Greeks who gave us the name Io, evidently during an economic downturn when the government could no longer afford costly consonants and was limited to printing all its official documents with cheap, plentiful vowels. (This may have affected the accuracy of the state newspaper when it reported Socrates’ last word as Aaaaaaaa!!!) Io was the name of one of the romantic conquests of Zeus, the mythical king of the heavens, who also wooed and won Europa, Ganymede, and Callisto. Zeus was known as Jupiter to the Romans, and so when Galileo discovered four moons around the planet Jupiter in 1610, he named them after these four divine paramours.

What got me thinking about the whole Io issue was a recent news release from the International Astronomical Union (IAU)--a sort of United Nations for the world’s astronomers--announcing that it had at last chosen names for the six new moons Voyager 2 discovered around Neptune in 1989. When Voyager was launched, astronomers knew of only two moons circling the giant planet, but as the probe got close it spotted these half-dozen more. Onboard computers radioed the news to NASA in a series of beeps and boops that translated loosely as: Look what I found! Can we keep ’em? Huh? Can we? Please? Huh? NASA was reportedly skeptical but after a series of high- level meetings finally radioed back: Fine. But if those moons wander off into some elliptical orbit, we’re not chasing after them, mister.

Like anyone who’s just picked up a few strays, the first thing officials had to do (after putting down newspaper, of course) was choose some names--preferably names that made sense together. Manny, Moe, and Jack were only half as many handles as were needed, and even Crosby, Stills, Nash, and Young fell short (unless you included the session drummer and the bass player, but who wants a moon named Fuzzy Samuels?). Happily for students of astronomy who don’t want to spend eternity humming Our House whenever they think about Neptune, the naming of heavenly bodies involves more than just picking something that reminds you of where you were during the Summer of Love.

For naming comets, the rules of the celestial name game are rather easy and are grounded in the childhood concept of finders keepers. In other words: You find and track the comet, you get to name it after yourself. Comet Kohoutek was discovered by the astronomer Lubos Kohoutek. Comet Halley was seen by the ancients, but its trajectory was first plotted by Edmond Halley. Comet Cleanser was found by Bob and Harriet Cleanser, a pair of amateur astronomers known for their abrasiveness.

However, things were not always so straightforward or sensible. People have been observing comets for thousands of years, says astronomer Gareth Williams of the Harvard-Smithsonian Center for Astrophysics, but before the middle of the eighteenth century there were no formally agreed- upon names or designations for any of them.

Williams, who works in the department that catalogs and christens new comets, explains that the seminal year in comet watching was 1759, when French astronomer Charles Messier dragged his telescope into a field and began the first systematic effort to document all known or suspected comets. Messier was aware of hundreds of reported comet sightings, Williams explains, but how many were reliable and how many were return sightings of the same comet, no one knew. He kept his survey going off and on from 1759 to 1798 and eventually compiled a catalog of about a hundred new heavenly objects, thirteen of which were confirmed comets.

Long on family pride, if short on imagination, Messier decided to name all his comets, well, Messier. While this was extremely gratifying to the Messier clan, it was enormously confusing to other astronomers. (It also caused occasional stampedes when Messier went out into the yard and tried to call just one comet into the house.) To clear things up, Messier added the year of discovery to the name of each comet. If more than one comet was spotted in a single year, he numbered them in the order that each reached perihelion--its closest approach to the sun. His discoveries thus bore such unpoetic names as Comet Messier 1790-I, Comet Messier 1790-II, and so on. Happily, Messier eventually got out of the sky-watching business, allowing the 800-plus comets discovered since to answer to different names.

Along with the job of tracking and naming comets goes the job of tracking and naming minor planets. This term, of course, is science code for asteroids, which is itself science code for really big flying rocks--but if you use a name like that you don’t have a chance of getting funding.

Asteroids are found throughout the solar system, but they are especially plentiful between the orbits of Mars and Jupiter, where they congregate, or cluster, into a band, or belt, that could disable, or squish, a passing spacecraft. The first asteroid was discovered in 1801 by Italian astronomer Giuseppe Piazzi, who at first thought he had discovered a comet, which he named Ceres, after the Roman goddess of agriculture. Alas, later observations proved the comet to be nothing more than a boulder measuring some 600 miles across, helping establish the now- popular dictum that if you really want to get famous, you shouldn’t let anyone make later observations.

Nevertheless, Piazzi’s discovery did pique interest in the Martian-Jovian region of the solar system, which over time was found to contain tens of thousands of asteroids, many of which are now thought to measure less than an inch across. For handle-happy astronomers, of course, this presented a problem. If the Canadian Football League can’t find names for just eight teams without calling two of them the Roughriders, how could astronomers name 20,000 or 30,000 asteroids without starting to repeat themselves, too? What’s more, how could they hope to keep track of all the orbiting rocks, assuring themselves that the asteroid they call Hekyl today isn’t confused with its neighbor Jekyl tomorrow? Once again, Williams and his colleagues have a way.

When an asteroid is reported, Williams says, we first check to see if it’s known; if it’s new we give it a temporary numerical designation, similar to the ones Messier gave comets. A typical asteroid might be named 1991-UP2. The 1991, of course, refers to the year the asteroid was found. Astronomers then assign each half-month in the year a letter code, beginning with A for the first half of January, B for the second half, C for the first half of February, and so on. You go through the year like that, skipping I (it looks too much like a 1), and wind up at Y for the second half of December. The first letter in an asteroid’s code tells you the two-week stretch in which the discovery was made. Thus, 1991- UP2 was discovered in the second half of October.

But suppose other asteroids were discovered in the same period? Williams has that covered too. After the first letter, he explains, you count through the alphabet again--once again skipping I--with each letter up to Z representing one asteroid. If the second letter is D, for example, your asteroid is the fourth one discovered in that two-week period. If more than twenty-five are discovered, you put a subscript one after the second letter, indicating you’ve counted through the whole alphabet once. If more than fifty were discovered, you put a subscript two, and so on. Asteroid 1991-UP2 turns out to be the sixty-fifth asteroid spotted in its two-week time frame.

Once you understand the code, you and your friends can spend many exciting hours calculating your very own asteroid numbers. If I myself were an inert, floating boulder, I’d be known as 1954-KA, since I was born on May 21, 1954, and so far as I know, my parents didn’t discover any other children that month. Typically, you’ll find your real name a lot more appealing than your space name, unless you happen to be Moon Unit Zappa, in which case you’d probably wish your father had used the astronomical designation.

Unlike the children of rock stars, asteroids aren’t stuck with unattractive labels for life. Once an asteroid is observed for several years and is known to be a discrete object in a predictable orbit, the person who first spotted it is given the privilege of naming it. After the name is chosen, it must be approved by a committee from the IAU.

There are seven members on the committee, from several different countries, Williams says, and they vet the name, making sure it’s original and not objectionable to anyone. (A good thing, too--I couldn’t stomach 10,000 asteroids named Jason or Jennifer.)

Even if astronomers can come up with enough names for every asteroid ever found, they will almost certainly fall short when it comes to naming galaxies. While comets have been found in the hundreds and asteroids in the thousands, galaxies are usually spotted in what scientists refer to as oodles. The first description of a galaxy--our own--came from Galileo. With the aid of an early telescope, he discovered that the Milky Way--the shimmery cloud that splits the night sky--is in fact a discrete cluster of millions of stars viewed edge on.

Galileo didn’t have to name the heavenly spangle: our galaxy’s appearance had already earned it its name (galakt means milk in Greek). But it was Galileo’s friend John Milton who gave the name its popular pizzazz. Milton wrote in Paradise Lost, The Galaxy, that Milky Way/Which nightly as a circling zone thou seest/Powder’d with stars . . . The rest is poetry.

In the years since, a number of scientific stick-in-the-muds have complained that Milky Way is a rather undignified name for such a spectacular cosmic formation. Recently released documents, however, reveal that Milton was this close to penning, The Galaxy, that Almond Joy, so perhaps we should all thank our lucky you-know-whats.

It would be another three centuries before American astronomer Edwin Hubble would prove the Milky Way was not alone among the universe’s giant star clusters. When other galaxies were discovered, however, they needed names of their own.

Among the objects Hubble recognized as galaxies were the Large and Small Magellanic Clouds, irregular companion galaxies of the Milky Way lying within a quarter-million light-years of Earth. The Magellanic Clouds were first named in the early sixteenth century, after they were spotted and described by the crew of the explorer Ferdinand Magellan--or Ferdinand Cloud, I forget which. Also included in Hubble’s study was Andromeda, a spiral galaxy like the Milky Way, located about 2.2 million light-years from Earth. That spot of light was first noticed by Arab astronomers, who named it after the mythological Ethiopian princess Andromeda. The princess was picked up by the Greeks, who put her in their own myths. They chained her to a cliff and set a monster to keep watch over her. Eventually she was rescued by one of Zeus’ sons, Perseus, who later became her husband. (Perseus, to his credit, was philosophical when later informed that his new bride was not a princess at all, but a galaxy, reportedly responding: That’s okay, there’s just more of her to love.)

As telescopes improved, the population of known galaxies began multiplying into the hundreds and then the thousands and then the millions. The galactic population explosion meant that astronomers could no longer afford the luxury of poetry, and they began cataloging galaxies with the astronomical equivalent of social security numbers. Trust me, their names are just too boring to go into--it’s a little like curling up with the phone book for Greater Uppsala.

Of course, the job of listing and labeling millions of galaxies makes the IAU’s recent job of picking handles for a mere half-dozen Neptunian moons seem like child’s play. However, the business of naming such close-to-home objects has a long and somewhat tortured history.

The first attempt to give names to the solar system’s permanent bodies was made by the Babylonians, who, observing how the inner planets meandered all over the sky, dubbed them wild sheep. The term seemed okay, but when the Babylonians tried to use it in conversation--like when someone would say, Do you think life exists on any other wild sheep?--all the other ancient peoples laughed at them. Later the Greeks came along, observed the same planets, and dubbed them planetes. They gave the bodies this name because a) that’s what they were, for goodness’ sake, and b) planet means wanderer in Greek.

The next step, of course, was naming each individual planet. The Greeks and Romans both had an array of mythological characters whose names would be suitable for the job, but in the end, the Romans also had things like catapults and spears, so their names won. Most of the names chosen were pretty elegant--and well suited to the nature of each planet. For example, Mercury, the fastest-moving planet, was named after the Romans’ celestial messenger. Venus, the brightest and loveliest planet, was named after the heavenly empress of love and beauty.

For the most part, the system worked well, but along the way there were some near breakdowns. In the late eighteenth century, after a seventh planet was discovered, there was some talk of naming it--I’m not kidding here--Herschel, in honor of its discoverer, William Herschel. Astronomers soon realized, how-
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