The asteroid Ceres
3 April 2023
An asteroid is a small, rocky or metallic body that orbits a star. In our solar system, asteroids are concentrated in a belt between Mars and Jupiter. The name was coined by astronomer William Herschel in 1802 from Greek and Latin roots: ἀστήρ (star) + -oides / -οειδής (-oid, resembling). So, an asteroid resembles a star, and indeed, with the telescopes of the early nineteenth century, astronomers could not discern any asteroid’s disc, as they could with a planet. So, while they appeared to be point sources to nineteenth-century astronomers, like stars, asteroids moved like planets across the background of stars.
Herschel proposed the name asteroid in a 6 May 1802 paper given at the Royal Society:
With this intention, therefore, I have endeavoured to find out a leading feature in the character of these new stars; and, as planets are distinguished from the fixed stars by their visible change of situation in the zodiac, and comets by their remarkable comas, so the quality in which these objects differ considerably from the two former species, is that they resemble small stars so much as hardly to be distinguished from them, even by very good telescopes. It is owing to this very circumstance, that they have been so long concealed from our view. From this, their asteroidical appearance, if I may use that expression, therefore, I shall take my name, and call them Asteroids; reserving to myself, however, the liberty of changing that name, if another, more expressive of their nature, should occur. These bodies will hold a middle rank, between the two species that were known before; so that planets, asteroids, and comets, will in future comprehend all the primary celestial bodies that either remain with, or only occasionally visit, our solar system.
I shall now give a definition of our new astronomical term, which ought to be considerably extensive, that it may not only take in the asteroid Ceres, as well as the asteroid Pallas, but that any other asteroid which may hereafter be discovered, let its motion or situation be whatever it may, shall also be fully delineated by it. This will stand as follows.
Asteroids are celestial bodies, which move in orbits either of little or of considerable excentricity [sic] round the sun, the plane of which may be inclined to the ecliptic in any angle whatsoever. Their motion may be direct, or retrograde; and they may or may not have considerable atmospheres, very small comas, disks, or nuclei.
As mentioned, most of the asteroids in our solar system orbit between Mars and Jupiter, and the term asteroid belt has been in use since at least 1867. That term appears in Jacob Ennis’s book The Origin of the Stars, published that year:
SECTION XXXIII.
Asteroids, Meteorites, and Comets.
Asteroids.
The orbits of the asteroids are generally interlinked; that is, they are so near together that the perihelion distance of an outer asteroid is nearer the sun than the aphelion distance of an inner one. They are probably a few hundred in number, about eighty having been discovered in the last twenty years, and they are included within a belt about 150,000,000 miles broad. In view of the dimensions of the rings which formed the planets as given in the thirtieth section, we cannot suppose that a single ring occupied all the space within the asteroid belt.
Asteroid belt is the term generally used in scientific literature, but one often finds asteroid field used in the realm of science fiction. This term dates to at least 1942, when it appears in Raymond Jones’s short story Starting Point:
Jack put in a call to the nearest safety monitoring ship.
“Yes, the Asteroid Kid finally took off, and what a cockeyed curve he’s running. You better pull him out and disqualify him before he kills himself.
“The crazy kid, instead of curving up over the asteroid field, he’s smashing through the thick of them at nearly four gees. He’ll bust a gut even if he don’t hit another asteroid.”
In science fiction, asteroid fields are often depicted as a danger to space navigation, but in reality that’s not the case, at least not in our solar system. For while there are around a million asteroids that we know of, space is what astronomers call “very big,” and the distance between any two asteroids is vast. The chance of a spacecraft hitting one by accident is very low.
Of the million or so asteroids, a few dozen have common names. The first four asteroids to be discovered were Ceres, Pallas, Juno, and Vesta. These were discovered in the opening years of the nineteenth century, with many more to follow in subsequent decades.
Ceres is the largest of the asteroids and the first to be discovered, by Giuseppe Piazzi in January 1801. Named by Piazzi for the Roman goddess of agriculture, it was classified at first as a planet, but it was later downgraded to asteroid after others of its type started to be found. Today, it is officially designated as a dwarf planet by the International Astronomical Union. The name appears in English by the end of 1801, as recorded by the Hampshire Chronicle of 28 December:
Letters from Berlin state, that the celebrated astronomer Bode, has received from M. De Piazzi, of Palermo, two letters, in which he concurs with M. Bode, that the star discovered on the 13th of January last, is a planet. The German astronomers propose to call it Juno, in analogy with the names of the other Planets, but M. De Piazzi wishes it to be called Ceres Fernandia, in allusion to Sicily, the ancient dominion of Ceres, and to the reigning monarch.
The next to be discovered was Pallas, found by Heinrich Wilhelm Matthäus Olbers on 28 March 1802. In Greek mythology, Pallas was the foster-sister of Athena, and Athena accidentally killed her in mock combat. The two were closely associated, and Athena is often referred to as Pallas Athena—the Palladium was a Trojan statue of Athena that protected the city, until it was stolen by Odysseus and Diomedes, enabling Troy to be sacked. The first mention of the asteroid’s name in English that I’m aware of is by Herschel in the above quotation.
Juno would be next, discovered on 1 September 1804 by Karl Ludwig Harding. Again, the first mention of the name in English would be by Herschel, in a paper given before the Royal Society on 6 December 1804:
Mr. Bode's stars 19, 25 and 27 Ceti are marked 7m, and by comparing the asteroid, which I find is to be called Juno, with these stars, it has the appearance of a small one of the 8th magnitude.
With regard to the diameter of Juno, which name it will at present be convenient to use, leaving it still to astronomers to adopt any other they may fix upon, it is evident that, had it been half a second, I must have instantly perceived a visible disk. Such a diameter, when I saw it magnified 879,4 times, would have appeared to me under an angle of 7’ 19",7, one half of which, it will be allowed, from the experiments that have been detailed, could not have escaped my notice.
Juno, of course, is the Roman name for the goddess married to Jupiter.
The second largest asteroid would be the fourth to be discovered, this time by Olbers on 29 March 1807. Dubbed Vesta, after the Roman goddess of hearth and home, the first English mention of the name is in a translation of a letter by John Jerome Schroeter published by the Royal Society on 28 May 1807. The German original is from 12 May:
At our very first observations with magnifying powers of 150 and 300 applied to the excellent new 15-feet reflector, we found the planet Vesta without any appearance of a disc, merely as a point like a fixed star with an intense, radiating light, and exactly of the same appearance as that of any fixed star of the sixth magnitude. In the same manner we both afterwards saw this planet several times with our naked eyes, when the sky was clear, and when it was surrounded by smaller invisible stars, which precluded all possibility of mistaking it for another. This proves how very like the intense light of this planet is to that of a fixed star.
As the observations and measurements of Ceres, Pallas, and Juno, were made with the same eye-glasses but with the 13-feet reflector, we soon after compared the planet Vesta with the same glasses of 136 and 288 times magnifying power in the 13-feet reflector. In both these telescopes its image was, without the least difference, that of a fixed star of the 6th magnitude with an intense radiating light; so that this new planet may with the greatest propriety be called an asteroid.
Sources:
Ennis, Jacob. The Origin of the Stars. New York: D. Appleton, 1867, 292. HathiTrust Digital Archive.
Herschel, William. “Experiments for Ascertaining How Far Telescopes Will Enable Us to Determine Very Small Angles, and to Distinguish the Real from Spurious Diameters of Celestial and Terrestrial Objects” (6 December 1804). Philosophical Transactions of the Royal Society, 95, 58. HathiTrust Digital Archive.
———. “Observations on the Two Lately Discovered Celestial Bodies” (6 May 1802). Philosophical Transactions of the Royal Society, 92, 228–229. Hathitrust Digital Archive.
Jones, Raymond F. “Starting Point.” Astounding Science Fiction, 28.6, February 1942, 75/2. HathiTrust Digital Archive.
“London.” Hampshire Chronicle (England), 28 December 1801, 2/3. Gale Primary Sources: British Library Newspapers.
Oxford English Dictionary, second edition, 1989, s.v. asteroid, adj. and n., Vesta, n.
Sheidlower, Jesse, ed. Historical Dictionary of Science Fiction, 8 January 2021, s.v. asteroid field, n.
Schroeter, John Jerome. “Observations and Measurements of the Planet Vesta” (28 May 1807). Philosophical Transactions of the Royal Society, 97, 245. HathiTrust Digital Archive.
Image credit: NASA / JPL-Caltech / UCLA / MPS / DLR / IDA / Justin Cowart, 2015. Wikimedia Commons. Public domain image.