Jan 112018
 

On this date in 1787 William Herschel discovered 2 moons of Uranus that were later named Titania and Oberon. I have covered Herschel (http://www.bookofdaystales.com/william-herschel/ ) and Uranus (http://www.bookofdaystales.com/uranus/ ) already in my posts. Now I would like to talk about the complex moon system of Uranus, and, especially, the way in which they got their names. Herschel was terrible at giving names to objects in the solar system and, in fact, did not name the moons of Uranus that he discovered (and, to make matters worse, he claimed to have observed 4 other moons that do not exist). Furthermore, he gave the name “George’s Star” to Uranus when he discovered it, because he wanted to toady up to George III. Astronomers in other countries were not amused.

Uranus has 27 known moons, all of which are named after characters from the works of William Shakespeare and Alexander Pope. Uranus’ moons are divided into three groups: 13 inner moons, 5 major moons, and 9 irregular moons. The inner moons are small dark bodies that share common properties and origins with Uranus’ rings. The 5 major moons are massive enough to have reached hydrostatic equilibrium, and 4 of them show signs of internally driven processes such as canyon formation and volcanism on their surfaces. The largest of these 5, Titania, is 1,578 km in diameter and the eighth-largest moon in the Solar System, and about one-twentieth the mass of Earth’s Moon. The orbits of the regular moons are nearly coplanar with Uranus’s equator, which is tilted 97.77° to its orbit. Uranus’ irregular moons have elliptical and strongly inclined (mostly retrograde) orbits at large distances from the planet.

Titania

Oberon

Titania and Oberon were spotted by Herschel six years after he had discovered the planet itself. Later, Herschel thought he had discovered up to six moons and perhaps even a ring. For nearly 50 years, Herschel’s instrument was the only one with which the moons had been seen. In the 1840s, better instruments and a more favorable position of Uranus in the sky led to sporadic indications of satellites additional to Titania and Oberon. Eventually, the next two moons, Ariel and Umbriel, were discovered by William Lassell in 1851. The Roman numbering scheme of Uranus’ moons was in a state of flux for a considerable time, and publications hesitated between Herschel’s designations (where Titania and Oberon are Uranus II and IV) and William Lassell’s (where they are sometimes I and II). With the confirmation of Ariel and Umbriel, Lassell numbered the moons I to IV from Uranus outward, and this finally stuck. In 1852, Herschel’s son John Herschel gave the four then-known moons their names.

No other discoveries were made for almost another century. In 1948, Gerard Kuiper at the McDonald Observatory discovered the smallest and the last of the five large, spherical moons, Miranda. Decades later, the flyby of the Voyager 2 space probe in January 1986 led to the discovery of ten further inner moons. Another satellite, Perdita, was discovered in 1999 after studying old Voyager photographs.

Uranus was the last giant planet without any known irregular moons, but since 1997 nine distant irregular moons have been identified using ground-based telescopes. Two more small inner moons, Cupid and Mab, were discovered using the Hubble Space Telescope in 2003. As of 2016, the moon Margaret was the last Uranian moon discovered, and its characteristics were published in October 2003.

When the responsibility of naming the first four moons of Uranus was given to John Herschel, instead of assigning them names from Greek legend, he named them after magical spirits in English literature: the fairies Oberon and Titania from William Shakespeare’s A Midsummer Night’s Dream, and the sylphs Ariel and Umbriel from Alexander Pope’s The Rape of the Lock (Ariel is also a sprite in Shakespeare’s The Tempest). The reasoning was presumably that Uranus, as god of the sky and air, would be attended by spirits of the air. Subsequent names, rather than continuing the airy spirits theme (only Puck and Mab continued the trend), have focused on Herschel’s source material. In 1949, the fifth moon, Miranda, was named by its discoverer Gerard Kuiper after a thoroughly mortal character in Shakespeare’s The Tempest. The current IAU practice is to name moons after characters from Shakespeare’s plays and The Rape of the Lock (although at present only Ariel, Umbriel, and Belinda have names drawn from the latter; all the rest are from Shakespeare). At first, the outermost moons were all named after characters from one play, The Tempest; but with Margaret being named from Much Ado About Nothing that trend has ended. The moons’ names come from the following sources:

The Rape of the Lock (Alexander Pope):

Ariel, Umbriel, Belinda

Plays by William Shakespeare:

A Midsummer Night’s Dream: Titania, Oberon, Puck

The Tempest: (Ariel), Miranda, Caliban, Sycorax, Prospero, Setebos, Stephano, Trinculo, Francisco, Ferdinand

King Lear: Cordelia

Hamlet: Ophelia

The Taming of the Shrew: Bianca

Troilus and Cressida: Cressida

Othello: Desdemona

Romeo and Juliet: Juliet, Mab

The Merchant of Venice: Portia

As You Like It: Rosalind

Much Ado About Nothing: Margaret

The Winter’s Tale: Perdita

Timon of Athens: Cupid

To quibble, just a tad, I’d have to say that Cupid is a bit of a cheat, or at least a cheat in calling the name one that is derived from Timon of Athens rather than from the ancient Roman pantheon. Obviously, the naming of the planets after Greek and Roman gods dates back to antiquity (in the West). Breaking the tradition with planetary satellites, comets, and whatnot seems fine. However, focusing on Shakespeare for the moons of Uranus does seem awfully ethnocentric. The naming of moons has been the responsibility of the International Astronomical Union’s committee for Planetary System Nomenclature since 1973. That committee is known today as the Working Group for Planetary System Nomenclature (WGPSN). Prior to its formation, the names of satellites had varying histories. The choice of names was often determined by a satellite’s discoverer. However, historically some satellites, such as Titania and Oberon were not given names for many years after their discovery. The longest is probably Titan, a moon of Saturn, discovered by Huygens in 1655, but not named until 1847, almost two centuries later.

The recipe of the day has to be fairy cakes, I think. My twisted mind thinks of them as being like delightful little moons, as well as evocative of Shakespeare’s characters. I’ll give you the basic recipe and then leave it to you to decorate them as you please. I’ve always liked them with little wings. There’s a small gallery of ideas at the end. They are about the easiest cakes to make that I know of. I used to assist my mum making them when I was little.

Fairy cakes

Ingredients

110g/4oz butter, softened at room temperature
110g/4oz caster sugar
2 eggs, lightly beaten
1 tsp vanilla extract
110g/4oz self-raising flour
1 or 2 tbsp milk

Instructions

Preheat the oven to 180˚C/350˚F and line 2 x 12-hole cake tins with paper cases.

Cream the butter and sugar together in a bowl until pale. Beat in the eggs, a little at a time, and then stir in the vanilla extract.

Fold in the flour gently with a wooden spoon. Add the milk very slowly until the mixture is a soft dropping consistency, but not too wet. Spoon the mixture into the paper cases so that they are half full.

Bake in the oven for 8-10 minutes, or until the cakes are golden-brown on top and a toothpick inserted into one of the cakes comes out clean. Set the cake tins aside to cool for 10 minutes, then remove the individual cakes from the tins and cool them on a wire rack.

Decorate the cakes as you please with icing, whipped cream, sprinkles, or what-have-you.

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