221 Eos is a K class (more about this in a minute) main belt asteroid discovered by Johann Palisa on January 18th 1882. It’s about 100 km wide, weighs in at a healthy six million trillion tonnes (give or take a few hundred thousand) and is quite dim at magnitude 7.67.
Eos lends its name to an extensive family of asteroids, all sharing roughly similar orbits, and all thought to have originated from an almighty collision some time in the distant past, which the latest best guesses put at around a billion years ago. About 300 members of the family are known, all being similar to S-types, but not identical, so they get their own category, the aforementioned K-type.
Eos was named after the Greek goddess of the dawn, shown above in her winged chariot. She was the sister of Helios (Sun) and Selene (Moon) and it was her job to open up heaven in the morning so that Helios could do his thing.
Also today, asteroid 468 Lina, a member of the Themis family, was discovered today in 1901 by Max Wolf and named after the family housemaid. It’s probably best if I don’t speculate as to why that might be.
Asteroid 410 Chloris was discovered on January 7th 1896 by Auguste Charlois. It’s a large, C-type, main-belt asteroid of approximately 115 km diameter, and lends its name to a family of similar bodies.
The Chloris family contains an unknown number of members, obviously, because we can never be sure they’ve all been found. But even if we only consider those asteroids we know about, there is still some uncertainty surrounding how many asteroids there are in the family, depending on which method you use to determine whether a particular asteroid should be included or not. For example, using hierarchical clustering, the family has 21 members, but using wavelet analysis, there are 27. One day in the distant future, when I lose the will to live, I’ll try to explain these methods. In the meantime, here are the facts and figures.
Longitude of ascending node
The name Chloris comes from a Greek work meaning something along the lines of pale greenish (think “chlorophyll”). There are several mythological characters with the name, but the one apparently invoked in this case was one of the Niobids, the fourteen children of Niobe and Amphion, most famous for being nearly all killed by Apollo and Artemis. Chloris had been born with the name Meliboea, but was turned permanently palid by the aforementioned ordeal (which she survived) and changed her name to something suitably pale and interesting.
The photograph (above) shows a detail from a Roman sarcophagus found near the Via Appia in Rome in 1824, and now housed in the Glyptothek in Munich, a museum built specifically to house the Greek and Roman sculptures of King Ludwig I of Bavaria.
Aside: I can’t let this post go by without directing you to an exceptional recording by Susan Graham and Roger Vignoles of À Chloris, one of my favourite songs by the Venezuelan composer Reynaldo Hahn. CLICK HERE first to hear it, they buy the album (“La Belle Epoque”, Sony, SK60168). I apologise in advance for the adverts YouTube will fire your way.
Saturn’s second-largest moon, Rhea, was discovered on this day in 1672 by Giovanni Domenico Cassini, who had presumably finished his Christmas shopping early.
Like our own Moon, Rhea always keeps one side, the one you can’t see in this photo, facing towards the parent planet, and from the above view of Rhea’s cratered anti-Saturnian surface, this does look to be a place very much like the Moon we are familiar with down here. But appearances can be deceptive. For a start, it’s a lot smaller than the moon, and if it soft-landed on the Earth it would fit quite comfortably inside the borders of Zaïre (in this country people usually use Wales as the benchmark for large areas, but I felt like a change). Secondly, although it looks nice and rocky,Rhea is thought to be comprised of as much as three-quarters ice, and only one quarter rock (studies of Rhea’s inertia suggest that it doesn’t even posses a rocky core).
Rhea is named after a Titaness of some standing, the daughter of Uranus and Gaia. As mother of Zeus and Hera, she was grandmother or great-grandmother to almost all the Olympian gods and goddesses worth mentioning.
There are several suggestions doing the rounds concerning the origin of the name Rhea. It may derive from the word for “flow”, or it could have a root in a much older word for “powerful”. But the guy who named the large, flightless, South American bird after her was almost certainly thinking of a derivation of the Greek έρα, meaning “ground”.
Saturn’s moon Epimetheus, discovered today in 1966 by Richard Walker, is a non-identical twin. It, and its larger brother, Janus, which had been discovered three days previously by Audouin Dollfus, fly round Saturn in almost identical orbits (their mean orbital radii differ by a mere 50km or so). Obviously, at the time of discovery, with only the evidence of Earth-based telescopes to go by, this caused a certain amount of confusion among astronomers trying to work out where the supposed new single moon was. At the time it was thought, also fairly obviously, highly unlikely that two moons would share the same orbit without hitting each other.
It is possible that at some time in the past Epimetheus and Janus were part of a single larger body, but if that is the case it is likely to have been a very long time ago. Both are heavily cratered, and their surface features display softening of their edges by the accumulation of dust, suggesting nothing much has changed there for some time.
Epimetheus was, in Greek mythology, a Titan (nowadays the name of a rather larger Saturnian moon), brother of Prometheus(also a moon of Saturn). The pair were sons of Iapetus (another Saturnian satellite). Epimethius was, according to some myths, married to Pandora (and guess what she gave her name to?).
Epithemius was given the job, shortly after the creation of the Earth, of finding a positive trait to give to each of the newly designed animals. Unfortunately he ran out of good characteristics with one animal remaining, which you’ve probably already guessed was man. That’s when Prometheus came along and gave man the gift of fire, after which it all went downhill.
As it happens, though, they do share the orbit, and they don’t hit each other. One moon does catch the other up every four years, but interactions between their gravities causes the inner moon to move faster (which causes it to move to a higher orbit) and the outer moon to slow down, causing its own orbit to drop a little. So they actually exchange places, which is why I’m not going to call them the fifth and sixth moons, because they are each neither and both.
Launch, in 1958, of SCORE, the world’s first communications satellite (Signal Communications by Orbiting Relay Equipment). The launch, from Cape Canaveral, was via an Atlas-B 10Brocket.
Asteroid 211 Isolda, discovered on December 10th 1879 by Johann Palisa,is about as average as asteroids get. It’s dark, in the main belt, C-type, 150-ish km across, and has an orbital period of 5.3 years.
So today, as well as mentioning those orbital characteristics of Isolda with which we all should now be familiar from previous posts (aphelion – 3.53 AU; perihelion – 2.54 AU; semi-major axis – 3.04 AU, and longitude of ascending node – 263.8°) I’m going to say that Isolda has an eccentricity of about 0.16.
Eccentricity is another fairly simple concept: it’s got very little to do with the behaviour of the English upper classes (you shouldn’t confuse eccentricity with lunacy) but a lot to do with the orbit of almost everything in the solar system being non-circular. Eccentricity, if we’re talking about planets, moons, asteroids and most known comets, will be measured on a scale somewhere between zero (completely circular) and one (an “escape” orbit). Planets have a fairly low eccentricities (Earth = about 0.017); asteroids are a bit more wayward (their average is ten times greater, at 0.17), and comets can be anything, with values near to, or even in excess of, 1.0 (eccentricities of more than 1 are reserved for comets that are being flung out of the solar system following their solar fly-by). Neptune’s moon Triton has the lowest known eccentricity, at 0.000016. This is about as circular as can be accurately measured.
Isolda, of course, is named after Isolde, (or Iseult of Ireland) the lover of Sir Tristan of Arthurian legend and Wagnerian opera.
Today’s photograph shows husband and wife team Ludwig and Malvina Schnorr von Carolsfeld, Wagner’s original 1865 Tristan and Isolde. Ludwig was a heldentonor, the dramatic tenor typical of Wagnerian protagonists. Soprano Malvina was the daughter of the Portuguese consul in Copenhagen, and was a great-grand-neice of David Garrick, giant of the English theatre.
1999 ⇒ Launch of ESA’s XMM-Newton (it stands for X-ray Multi Mirror Mission), the largest satellite to date to be launched by the European Space Agency (4 tonnes in weight and 10 meters long).
Asteroid 423 Diotimawas discovered from Nice by Auguste Charlois on December 7th, 1898. It’s in the main belt, is a C-type, is fairly large (approximately 170 by 140 km) and rotates once about its axis every 4.8-ish hours.
Diotima has a semi-major axis of a little over 3 AU. Semi-major axis sounds worse than it is. It’s just the longest radius of of an elliptical orbit.
Diotima was named, by the Heidelberg Astronomisches Rechen-Institut, or Astronomical Calculation Unit, after one of Socrates’ teachers, Diotima of Mantinea, a woman whose existence remains uncertain; the jury is still out on whether or not she was simply a creation of Plato. It is from the teachings of Diotima that we get the concept of platonic love. I can’t help thinking there’s a clue to her existence (or lack of it) in that name. Surely it would have been diotimic love?
We have slightly odd numbering here. Gemini 7 (VII) was launched on December 4th, 1965, after Gemini 5, but before Gemini 6A. Gemini 6 was obviously originally planned to go between 5 and 7, but had to be cancelled and rescheduled with an “A”.
The plan for Gemini 7 was to observe the effects of prolonged spaceflight on astronauts. The two-man crew, Frank Borman and James Lovell, circled the globe 206 times during their two week confinement. After 11 days they were joined briefly by Walter Schirra aboard Gemini 6A, and practiced rendezvousing (at closest approach during their extra-atmospheric ballet they were just one foot apart).
Gemini, of course, is the constellation that lies between Cancer and Taurus in the sky (and therefore in the zodiac) and is historically associated with the twin brothers Castor and Polydeuces (or Pollux if you prefer the later Roman name). I prefer Polydeuces myself, because the translation is “much sweet wine”, which you just don’t get with “Pollux”. Castor, as any rodentologist will tell you, is Greek for “beaver”.
The twins now immortalized in the heavens were collectively known to the Greeks as the Diskouri, or “sons of Zeus” (the noun Gemini is from Roman mythology). They also had twin half-sisters, even more famous than themselves: Helen (of Troy) and Clytemnestra.
Asteroid 82 Alkmene was discovered by the prolific German asteroid hunter Robert Lutheron November 27th 1864. It’s a medium-sized S-type main belt asteroid, orbiting the Sun every four and a half years.
Alkmene was named, at Luther’s request, by Karl von Littrow (director of the Vienna Observatory), Edmund Weiss (who would also become director of the Vienna Observatory, in 1878) and Theodor von Oppolzer (a professor at Vienna University), after the mother of Herakles. Zeus was the father, but didn’t go to any of the great lengths he normally employed in order to have his way with her. He simply disguised himself as Alcmene’s husband, Amphitryon, which was well below his normal level of inventiveness. But then again he’d already added a certain amount of deviation by going after her in the first place, as she was his great-granddaughter.
Today’s picture is a woodcut from a collection of 183 by the German artist Virgil Solis for a 1581 edition of Ovid’s Metamorphoses.
2011 ⇒ Discovery of the long period comet 2011 W3 Lovejoy by Terry Lovejoy, an australian amateur astronomer, responsible for the discovery of a further 4 comets..
Asteroid 128 Nemesis was discovered on November 25th 1872 by J C Watson. It’s a C-typeasteroid, estimated to be about 188km in diameter, and is one of the slower rotators, with a day of 39 hours. 128 Nemesis is the largest member of the Nemesis (or nemesian) family of asteroids, of which at least 129 have been identified by the Sloan Digital Sky Survey.
Nemesis, as the name might have already suggested to you, was the Greek goddess of retribution. She is generally thought to have been the mother of Helen of Troy and her twin sister Clytemnestra, as well as the more astronomically famous twins Castor and Pollydeuces (a.k.a. Pollux). Obviously, having two sets of twins, while unusual, was nowhere near bizarre enough for the Greeks, so the story goes that Nemesis, attempting to avoid Zeus (as usual) took the form of a goose. Zeus then turned into a swan, resulting of course in an egg from which her children are born.
Today’s asteroid, 107 Camilla, was discovered on November 17th 1868 by Norman Robert Pogson. It is just about within the main belt, being a member of the Cybele Group, a collection of rocks lying on the outer edge of the belt, beyond the 2:1 Kirkwood Gap, and thought to be the result of the break up of a much larger object sometime long ago. Camilla herself is one of the larger asteroids, with a diameter of 209km putting her right up among the big guns of the asteroid belt.
Camilla is so-called after a queen of the same name from Roman mythology, suckled by a mare (in accordance with the obligatory bizarre upbringings of many mythological characters), and later to become an ally of the Rutuli, opponents of Aeneas in Virgil’s Aeneid. She is one of the many historical and mythological characters encountered by Dante Alighieri in “Limbo”, the first circle of Hell, in his Inferno.
Camilla (we’re back with the asteroid now) has two small satellite. The first to be discovered is of about 6 miles across (10 to 11 km), spotted in 2001 by astronomers at Towson University in Maryland, using images from the Hubble Space Telescope. At the time of writing this satellite is designated S/2001 (107) 1 but has no official name. I’m voting for Charles.
The second satellite, S/2016 (107) 1, is even smaller, probably just 3.5km across. It was discovered by the Very Large Telescope in Chile, in 2016.