ASTRONOMICAL NOMENCLATURE

by Greg Burns
AST Vice President
A Talk presented to the Astronomical Society of  Tasmania, April 30 2002


The study and science of astronomy is assisted by the use of language, and a knowledge of astronomical nomenclature is essential if both the professional and the amateur are to gain a good understanding of this broad field.
    Astronomical names broadly divide into ‘ancient’ and ‘modern’, with the modern names effectively beginning in the seventeenth century or later. The great ancient astronomer Ptolemy in the second century AD, recognised 48 northern constellation names and preceding him were generations of ancient Middle Eastern and Mediterranean astronomers giving stars both original and translated names.
    For the modern names we would have to include recent constellation names of the southern skies, the three outer planets of the solar system and the asteroids. We would also include comets and surface features on the planets and the planetary satellites that have only been recently discovered and also the names and the terminology applied to deep sky objects such as galaxies.     
   
    The Sun: Solar regions have their own peculiar terms, most come from physics due to our mechanism of solar understanding such as the photosphere, corona, flare, plasma, solar wind etc.
   
    The Planets: The planets apart from our Earth are all named from mythology, and all are familiar gods and one goddess. The planets are named after Roman deities who have Greek equivalents with the exception of Pluto, who was a Greek god with no Roman equivalent. It must also be remembered that only the first five planetary names are ‘ancient’, as only Mercury, Venus, Mars, Jupiter and Saturn are easily visible to the naked eye. Ancient astronomers (or astrologers) regarded seven heavenly bodies as planets. These were in order of their once accepted distance from the Earth, the Moon, Mercury, Venus, the Sun, Mars, Jupiter and Saturn. Hence the use of the phrase ‘the seven planets’ in medieval and even later writings. The five planets proper, however, were not originally known by their present names but by Greek names, and in Pythagoras’ day, (the sixth century BC) Mercury was called Stilbon (meaning ‘shining one’). Venus was known as either Hesperos (‘evening one’) or Phosphoros (‘light-bearing one’) or Eosphoros (‘bringer of the dawn’) and it was Pythagoras who proposed that these were all one and the same body. Mars was Pyroeis (‘fiery one’), Jupiter was Phaethon (‘glittering one’), and Saturn was Phainon (‘shining one’). It was then the turn of Aristotle, in the fourth century BC, to introduce personal mythological names for the five planets, and he renamed Mercury as Hermes star, Mars as Ares star, Jupiter as Zeus star, and Saturn as Cronos star. Then when the Greeks recognised that Venus was one and the same planet, they came to call it Aphrodite, and this name also occurs in the writings of Aristotle as well as those of his teacher Plato. The Greek names then passed to Ancient Rome, where they were translated by the names of those Roman deities who corresponded to the Greek, and these are the names that remain with us today for the planets.

    Mercury: The craters on Mercury are named after famous artists, musicians, painters and authors. Planitiae are named after the names for Mercury in different languages. Rupes after ships of discovery or scientific expeditions and valleys after radio telescopes. Only 3 astronomers are commemorated on Mercury. These are Antoniadi and Schiaparelli who both contributed to surface study and also Kuiper.

    Venus: We only know of this planet’s surface features by our clever use of radar mapping with the spacecraft Magellan. In the case of Venus, the only planet named after a Goddess, the International Astronomical Union has decided that women only should be honored. With the exception of the 3 features picked out by Earth-based radar, the map of Venus thus bears the names of women. They range from deities and mythological figures to heroines of our time. Features such as Aphrodite, Cleopatra, Diana, Helen, Guinevere and Eve.

    The Earth: There are specific names applied to the Earth in relation to astronomy. These are normally in regular use and include terms such as aurora, magnetosphere, Van Allen Belts, Zodiacal Light, and Gegenschein. They normally describe zones, regions or particular atmospheric phenomena and are derived from physics and discoverers.

    The Moon: Naming lunar features is the art of the selenonymist, and this began with the seventeenth century astronomer Michel Florent van Langren who published a map of the Moon in 1645 and had some three hundred names for the most prominent features. They were from biblical characters and saints to members of the Spanish aristocracy. These names on the whole did not survive and only three still appear on modern lunar maps. They are Catherina (for St Catherine), Cyrillus (for St Cyril) and Theophilus (for St Theophilus) and all are lunar craters. Two years later the German astronomer Johannes Hevelius published his famous Selenographia, or atlas of the Moon, with detailed maps of the surface and entirely new names. He simply transferred geographical names from the Earth. Most of his names have fallen into disuse, as Langren’s have, but one or two remain such as the Alps and the Apennines. It was however Hevelius’ idea (the opposite of Leonardo da Vinci’s suggestion) to assign dark lunar regions names associated with regions of water such as Oceanus (ocean), Mare (Sea), Lacus (lake), Palus (marsh) and Sinus (strait). The third Moon-Namer, Italian Francesco Grimaldi published a map of the Moon in 1651 and his names were to survive in the greatest numbers. His map had around three hundred names and was published in Naples by Italian astronomer Giovanni Riccioli as a part of ‘Almagestum Novum’ which was partially a tribute to Ptolemy’s great treatise on astronomy known as the ‘Almagest”. As Riccioli was the overall author of the work, he usually gets the credit for Moon names that were actually introduced by Grimaldi, which is rather unfair. Be that as it may, it was these names that became established, and today over two hundred of them are still in use for lunar features. Grimaldi named craters after famous ancient philosophers and men of learning. In recent times, more geographical names and the names of famous people have been added to selenography. These have come from Johann Schroter (1791) describing areas with a capital Roman letter or Roman number, or a small Greek letter, and Madler and Beer (1837) who both made contributions. The International Astronomical Union has approved recent namings.

    Mars: Martian nomenclature is essentially that introduced by Giovanni Schiaparelli of Milan between 1877 and 1884 which is partially derived from names in the Bible and classical mythology and partly from ancient place names of the Mediterranean region. Many of Schiaparelli’s names were officially recognised by the International Astronomical Union in 1958, but for others alternative names or spellings were adopted.

    Jupiter: Jupiter’s features are essentially zones and belts named after polar temperate and equatorial regions, with exceptions such as ‘the Great Red Spot”. Jupiter has satellites named more or less after mythological figures, and on Jupiter’s satellite Callisto, the craters are named after figures from Norse mythology.

    Saturn: has its famous ring system, which has some features named after historic astronomers. Also, Sir John Herschel named seven of Saturn’s satellites after mythological figures.

    Uranus: The planet was discovered on March 13th 1781 by William Herschel and the name suggested by J. E. Bode in the same year after the first ruler of Olympus. Satellites of Uranus are named after Shakespearean characters.

    Neptune: was named by J.J. Le Verrier in 1846 using the name from mythology. It follows that the satellites are also named from mythological characters.
        
    Pluto: The planet Pluto was discovered by the American astronomer Clyde Tombaugh in 1930. And, the actual name is on record as having been suggested by an 11-year old Oxford schoolgirl, Venetia Burney. She proposed the name to her grandfather over breakfast on the 15th March, two days after the announcement of the discovery. The name was approved and the following month the name Pluto was officially adopted.
        
    Comets: Comet naming is normally commemorative after the comet finder. There are exceptions to this such as Comet Halley that was not found by him but named after him, as he predicted its return.

    Asteroids and minor planets: In 1801, Italian astronomer Guiseppi Piazzi discovered the first of the minor planets subsequently to be named Ceres. As further minor planets were found they were named after classical or mythological figures. Soon so many were found that the traditional classical names began to run out! So other names were applied such as distinguished humans or even geographical names. Nearly 3000 minor planets have been named to date.

    Meteor Showers: Meteor showers are named after the constellation in which they appear to radiate from and meteorites after the region on Earth where they landed.

The Constellations: The oldest astronomical or astrological names are those of the signs of the zodiac. The Sumerians of the Middle East were thought to have given names to the constellations and later the ancient Greeks translated these names to a circle of animals. The Greek names were then translated by the Romans in the Latin forms familiar to us today. Later still, around the Middle Ages, each sign of the zodiac or its constellation name was assigned a particular symbol. It was the Greeks however that popularised constellation names to the peoples of other lands, if only through Ptolemy’s listing of 48 of them. Apart from the 12 of the zodiac, he recognised 21 in the Northern Hemisphere and fifteen in the southern. All of those listed by Ptolemy still exist with the exception of Argo Navis, which has now been subdivided into four smaller constellations.
    With trade and travel coming to the southern latitudes in the 16th century, came Magellan and many sky objects and constellations were named around this time including the Southern Cross, which has been known since 1520.
    It was the German astronomer Johann Bayer who set the first trend giving exotic ‘Southern seas’ names to nearly a dozen constellations Hevelius was the next constellation-namer of any magnitude and continued the ‘animal naming’ tradition but only in the northern hemisphere. One of the most prolific constellation – namers was Nicolas Lois de Lacaille. He introduced his own names for southern constellations in the mid-eighteenth century and they were nearly all of scientific instruments, and in particular those used in astronomy. When it comes to the names of the constellations, astronomers will almost always use the Latin name, and not talk of the Great Bear, but say Ursa Major. This will even apply to the Southern Cross, which is Crux Australis. Just six constellations, named after mythological characters, have names that are the same in both Latin and English: Andromeda, Cassiopeia, Cepheus, Hercules, Orion and Perseus. In 1930 the International Astronomical Union finally adopted a list of 88 official constellations and the boundaries were also delineated.

    The Stars: The peoples of the Middle East, in the earliest days, also named individual stars, and many of these are still popularly known today in their Arabic form. Some of the stars have Greek or Latin names.    A good example here is the star Proxima Centauri, which is a mixture of Latin and Greek, meaning ‘nearest one of Centaurus’. Greek names often relate to characters and incidents in classical mythology. Some stars such as Beta Centauri have several original names Hadar or Agena, making a total of three different names. It can be seen that astronomical names can be complex affairs, involving at least three ancient languages (Arabic, Greek and Latin)! It should not be assumed that the Arabic star names were the originals as the Arabians themselves translated many names that had arisen in the Middle East before them. Today astronomers use the ancient names of stars infrequently, preferring instead the binomial designation consisting of Greek letter plus the Latin name of the appropriate constellation in the genitive, such as Alpha Centauri rather than Rigil Kentaurus. It is also a general principal that the brightest star is the one named alpha, the second brightest Beta and so on. But there are several prominent exceptions to this rule. For instance, in Orion and Gemini, it is the Beta star that is the brightest, and as a result of the subdivision of the ancient large constellation of Argo Navis into smaller constellations, neither Vela nor Puppis have Alpha or beta stars at all. Moreover, a few constellations have gaps in the run of Greek letters, notably Carina, which has no Gamma or Delta, and also omits other letters. Some stars have different designations, with for example a Roman letter, not a Greek one. Such stars will not normally have an ancient name, but may have a modern English name, which is really more a descriptive nickname. An example is the Blaze Star, in the constellation of Corona Borealis. Its official designation is T Coronae Borealis. Such letters often apply to variable stars, and originated when the German astronomer Friedrich Argelander assigned the Roman letters R to Z to conspicuous and unnamed variable stars in each constellation. After Z he then adopted the double form RR through to ZZ. After this one must start again with AA and so on ending with QZ. This allows for 334 variables in each constellation, and if there are any more than that, one simply has the letter V (for variable) and counts from 334, thus having V.335 and so forth. Not all variables are designated this way. This system of Roman letters should not be confused with another usage of Roman letters for classifying stars according to their heat. The Roman letter system to develop this naming aspect was the one introduced in 1890 by the American astronomer Edward C. Pickering, director of the Harvard College Observatory, hence the system’s original name (Harvard System). The current version of this heat classification system requires a mnemonic to memorise the sequence. The one normally used by astronomers is: Wow! Oh Be A Fine Girl/Guy Kiss Me Right Now, Sweetie/Smack. This produces the sequence WOBAFGKMRNS. Stars in the W category (rarest) have surface temperatures up to 80,0000°C whilst S stars are around 2,600°C. The system is now known as the Yerkes System. Apart from these names and designations, some stars have popular or folknames such as the Dog Star and the Pole Star. Other names may be commemorative such as Barnard’s Star. The spelling of stellar names and the rendering of their foreign language names, especially in Arabic, can be a tricky matter and there may be notable variations between various source books. It is recommended to use the most consistent version of any particular name. Another way to identify stars is by numbers. In each constellation the stars are numbered in order of right ascension. These stars are usually referred to as Flamsteed numbers.

The Galaxies: Galactic nomenclature starts with our home galaxy the Milky Way, which is an English translation of the Latin ‘Via Lactea’ which is in turn a translation of the Greek ‘Kyklos Galaktikos’ meaning milky circle based on the Greek word for milk ‘gala’. Other terms that apply to galaxies usually refer to the constellation through which the galaxy is seen, the galaxy type, and to the peculiar characteristic of individual galaxies such as ‘The Whirlpool Galaxy’. Most galaxies are covered by the New General Catalogue or by the Messier list. Some galaxies such as Malin1 are commemorative.

Nebulae and clusters: Names of star groups or clusters, ranging from the Milky Way downwards, can be either English or Latin-based, in the latter case taking their name from the constellation with which they are associated, such as the Orion Nebula. Astronomers often use the English names given to various nebulae, galaxies and other asterisms (as star groups are sometimes called). So the Beehive Cluster, Eskimo Nebula and the Fish Mouth Nebula are just as acceptable as the most intricate star designation. However nebulae are also designated in two other ways, in one or other of two catalogues. The Andromeda Nebula (galaxy) is also known as M31 or NGC 224. The first of these means that it was assigned the serial number 31 in the catalogue compiled in the eighteenth century by Charles Messier, and his designations are still in use for those nebulae that can be seen with small telescopes. The second has letters standing for New General Catalogue. This was a more professional compilation of nebulae drawn up in 1888 by the Danish born astronomer John Dreyer and has been revised twice but is still very much in use, and in the Southern Hemisphere is essential, because Messier did not include any nebula south of declination –35°. Messier’s original catalogue ended at 103, but there are a few higher numbers added by later astronomers. NGC figures are found well into four figures.

Celestial Motion: Words such as declination and right ascension, zenith, nadir, great circles, celestial and galactic equators, celestial and galactic poles, conjunction, circumpolar, ecliptic and many other terms describe where astronomical objects or reference points are to be found in the sky. These astronomical terms are normally to be found in any good dictionary and are usually derived from the Latin language.

Physics: The language of physics has become more commonplace in astronomy, particularly since the study of cosmology began. The field of astrophysics is indeed huge and is beyond the scope of this talk. Probably the best guide to this language is to read respected regular publications such as Sky and Space and New Scientist magazine and the articles, which are well written, will have you impressing the neighbors in no time at all!

Annual Dates and Terms: Terms such as solstice and equinox are also derived from the Latin language and we owe a great deal to this historic language for providing a strong base for Earth-based astronomical terms.

Specific terms:
There are also many abbreviations used in star charts and tables. A good astronomical dictionary is invaluable in deducing what these mean. One can also usually find an addenda or appendix or bibliography in various publications (such as The Cambridge Star Atlas) that explain many abbreviations clearly. It pays to read any glossary included in astronomical publications. Also astronomical equipment has its own world of terminology which is developing rapidly and is also beyond the scope of this talk. However, most good astronomical periodical magazines carry good articles on equipment and knowledge can be gained quite quickly via these publications.
    All celestial names have to be approved by the International Astronomical Union, a large organisation that includes thousands of the world’s astronomers in its membership, and that holds a general assembly every three years to discuss new names and other topics. It is the only valid organisation with particular reference to the naming of stars.

Bibliology:
The Data Book of Astronomy – Patrick Moore.
Dictionary of Astronomical Names – Adrian Room.