October 24 – Ariel and Umbriel

We have a double-header today.  Two moons of Uranus, Ariel and Umbriel, were discovered on October 24th 1851 by Bolton-born William Lassell, brewer and keen amateur astronomer, who was in the fortunate position of being able to use his not inconsiderable wealth to fund the construction of impressive telescopes.

Let’s take a quick look at Ariel first, a reasonably large moon of just over 579 km radius, orbiting its parent at a distance of about 190,000 km.  It travels at a fantastic pace, completing an orbit of the vast planet below it in two and a half Earth days.

Ariel viewed from Voyager 2 (image credit: NASA)

Ariel viewed from Voyager 2 (image credit: NASA)

Of all the moons of Uranus, the surface of Ariel appears to be the youngest, evidenced by the lack of older, larger impact craters, and the presence of recent geologic activity.  It is also the brightest of the large Uranian moons, and is tidally locked (keeps the same face to the planet at all times).  Ariel has only been visited up close and personal by one mission, Voyager 2, and as far as I know there are no plans to make a return journey just yet.

If you’ discover a moon of Uranus you have two choices from which to choose a suitable name: Alexander Pope’s The Rape of the Lock, or the plays of William Shakespeare.  At the sugestion of Lassell, Ariel was chosen by Sir John Herschel, son of Sir William Herschel, the discoverer of Uranus.  It’s a good choice, as it falls into both categories.

Now we move outwards slightly to Umbriel, which gets its name from that of a sprite in Pope’s narrative poem.  It too was chosen by John Herschel.

View of Umbriel from Voyager 2, 1986 (image credit: NASA)

View of Umbriel from Voyager 2, 1986 (image credit: NASA)

Umbriel is the third farthest major moon from Uranus (Ariel is the second), and is the darkest of the major Uranian satellites.  We don’t yet know why Umbriel is so much darker than similarly sized bodies in orbit around Uranus, but I’m sure somebody’s working on it somewhere.  With a radius of 584 km, it is only slightly larger than Ariel, and, like it’s neighbour, it’s no slouch, travelling at the impressive rate of 16,800 km/hour, meaning a year on Umbriel takes about four and a half Earth days.

For, that sad moment, when the Sylphs withdrew
And Ariel weeping from Belinda flew,
Umbriel, a dusky, melancholy sprite,
As ever sully’d the fair face of light,
Down to the central earth, his proper scene,  
Repair’d to search the gloomy Cave of Spleen.

(The Rape of the Lock, Alexander Pope, 1714)


1601   –   Death of the Danish astronomer, Tycho Brahe, whose use of the title De Nova Stella to announce the supernova of 1572 led to the word nova being applied to all such phenomena.


1890   –   First meeting of the British Astronomical Association at the Hall of the Society of Arts in London. Unlike the already established Royal Astronomical Society, the BAA was open to female members, and even allowed them onto its council. One can only speculate of course, but I assume the RAS had somehow decided that night vision was improved by ownership of testicles.


1964   –   Launch of Kosmos 49 (DS-MG 2) to test orientation systems and study the magnetosphere.  The launch was from the Kapustin Yar site near Volgograd (previously known as Stalingrad). The mission was a short one, and the satellite’s orbit decayed on August21st the year after launch.


2004   –   Discovery of Saturn’s extremely tiny moon, Polydeuces by the Cassini Imaging Science team.


February 16 – Miranda

Also known as Uranus V, Miranda was discovered by Gerard P Kuiper on February 16th 1948, making it the last Uranian moon to be discovered by Earth-based observing equipment. We have some fairly good shots of Miranda’s southern hemisphere taken by Voyager 2, which paid a visit in 1986. These show this small moon (only one seventh the size of our own Moon) to be an interesting place, crossed by grooves and enormous canyons, some more than ten times deeper than the Grand Canyon. Miranda, in common with the other larger Uranian moons, is thought to be composed of mostly silicates and water ice.

Miranda (image credit: NASA)

Miranda (image credit: NASA)

Obviously there must always remain a degree of uncertainty regarding the composition of a place we’ve only been to once, rather fleetingly, for ‘Tis far off, and rather like a dream than an assurance (Act 1, Scene 2). Miranda is the only female character in Shakespeare’s The Tempest.


1880 – Asteroid 213 Lilaea discovered by C H F Peters. Lilaea is approximately 83 km across, has a year lasting four and a half Earth years, a day lasting just over 8 hours, and is named after a Naiad (water nymph).


1891305 Gordonia is a 49 km wide main belt asteroid, discovered by Auguste Charlois and named after his patron, James Gordon Bennett Jr, publisher of the New York Herald, and thought to be the man from whom we get the exclamation “Gordon Bennett!”.


1965 – launch of Pegasus 1, via Saturn I rocket number SA-9 from Cape Kennedy to study the effects of micrometeoroid impact, which it achieved by use of two giant wings, unfurled upon reaching orbit. Pegasus 1 remained operational until it was deactivated on August 29th 1968. It remained in orbit until 1978.


January 24 – Voyager 2 at Uranus

1986: Voyager 2 makes its closest approach to Uranus.  The seventh planet from the Sun was reached after a journey lasting more than eight years.  It was a great success, discovering ten new moons, and two new rings.

Three new Uranian moons discovered by Voyager 2 (image credit: NASA)

Three new Uranian moons discovered by Voyager 2 (image credit: NASA)

The moons shown in the above photograph are Portia, (1986/U1), Cressida (1986/U3), and Rosalind (1986/U4).

The rings of Uranus, viewed from Voyager 2 (image credit: NASA)

The rings of Uranus, viewed from Voyager 2 (image credit: NASA)

It isn’t clear whether the rings of Uranus were known prior to 1977 when they were discovered by Elliott, Dunham & Mink. William Herschel had reported seeing them almost 200 years previously, but he might have been making an educated guess, as they would have been very hard to see with the instruments available at the time.

Parting shot of Uranus by Voyager 2 (image credit: NASA)

Parting shot of Uranus by Voyager 2 (image credit: NASA)

As far as I know there are no definite plans to re-visit Uranus in the near future.  Several missions have been suggested, but it takes a long time to get there, making it expensive, and these days you need to prove that it’ll be worth it.


1882 – Birth of Harold Babcock in Edgerton, Wisconsin.


 

January 11 – Oberon and Titania

January 11th 1787 was a good day for William Herschel.  Not many of us get to discover even one major moon in a lifetime, but on this particular day in history Herschel was fortunate enough to find both the largest moon of Uranus, Titania, and the second largest, Oberon.

Oberon is the outermost major Uranian moon, and the ninth most massive moon in the solar system.  It is about 50/50 rock and ice, with the rock probably forming the core.  It’s quite “moonish” in appearance, being fairly dark and rather cratered by impacts like our own companion.  However, unlike our dry Moon, as well as being partly icy, Oberon may well have a layer of liquid water between the core and the mantle.

Oberon from Voyager 2 (image: NASA)

Oberon from Voyager 2 (image: NASA)

Titania is similar in appearance and composition to Oberon, but is less heavily cratered, possibly as a result of internal processes that removed some of the older cratering.  Both moons were probably formed in situ from an accretion disc.

Titania from Voyager 2 (image: NASA)

Titania from Voyager 2 (image: NASA)

Only Voyager 2 has ever been close enough to Uranus to capture good shots of Oberon and Titania.  It made its closest approach to the planet on January 26th 1986, but had already got to about 300,000 miles of Titania and 400,000 miles from Oberon two days earlier, at which time it took these photographs.


1865   –   German astronomer Johannes Franz Hartmann born.


 

August 29 – Margaret and 74 Galatea

Margaret (or Uranus XXIII) is, so far as I know, the only prograde irregular satellite among Uranus’ collection of, at last count, 27. It was discovered on August 29th, 2003 by Scott S Sheppard and David Jewitt using the 9.3m Subaru telescope at Mauna Kea, Hawaii.

A further satellite of Uranus was also confirmed on this day, but as the first sighting of S/2001 U2 (now known as Ferdinand) was an unconfirmed glimpse on August 13th 2001 we shall say no more about it for the next 50 weeks.

Margaret is named after a minor character in Shakespeare’s Much Ado About Nothing. She is the servant or chamber-maid of Hero, the beautiful daughter of Leonato.

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74 Galatea (discovered August 29th, 1862) was the third of five asteroids to be discovered by the German astronomer Ernst Wilhelm Leberecht Tempel (comets were more his thing – he found an impressive 21!).

Galatea is a large, dark, C-type main belt asteroid, and if it seems as though every asteroid I mention fits that description it’s because 75% of all known asteroids are C-types, and the main belt contains 93% of all the numbered minor planets.

Pygmalion and Galatea (by Falconet)

Pygmalion and Galatea (by Falconet)

Two possibilities exist for the choice of the name Galatea. Ovid tells us on the one hand that it was the name of the ivory statue carved by the sculptor Pygmalion, with which he fell in love. But on the other hand he also uses the name to describe a nereid (sea nymph) whose lover, the river spirit Acis was killed by a boulder thrown by Galatea’s jealous suitor, Polyphemus the cyclops. Ovid omits to discuss what kind of aim a cyclops would have.

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August 25 – Cupid and Mab

Today in 2003  –  Cupid and Mab, moons of Uranus, both of which had been too dim to see on Voyager photographs, discovered by Mark R Showalter and Jack J Lissauer using the Huble Space Telescope. Cupid was named after the character in Timon of Athens, and Mab after the queen of the fairies who is mentioned in Romeo and Juliet (and as a long-time fan I would also refer you to The Fairy Feller’s Master Stroke on the album Queen II).  Mab has unusual hobbies. She drives her chariot (which I believe is made from an acorn) up people’s noses to enable her to influence their dreams, and she is thought to decide who gets infected by herpes simplex.

The best picture I could find of Mab.

The best picture I could find of Mab.

Neither Cupid nor Mab could be described as impressive bodies.  Cupid measures about 18 km in diameter, while Mab is thought to be about 24 km.

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Asteroid 84 Klio discovered by R Luther in 1865.  Clio (or Klio or Kleio) was the muse of history.  A daughter of Zeus and Mnemosyne, she had one son, to whom she gave the butchly masculine name Hyacinth. Her own name is derived from the verb kleô, meaning to celebrate or make famous.

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1889 – Asteroid 287 Nephthys discovered by C F H Peters, and is the last of his incredible haul of 48 asteroids.  Nephthys is a large, S-type main belt asteroid, and for a change is named after a character from Egyptian mythology, the daughter of Nut and Geb, and sister of Isis.

Nephthys

Nephthys

I’m going to have to do some digging on Peters, because I find it hard to believe that after 28 years of tracking the things, he doesn’t have an asteroid named after him.  I’ve found two so far named after people called Peters, and he isn’t either of them.

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Voyager 2 makes its closest approach to Neptune on August 25th, 1989.  This was the end of a bit of a purple patch for NASA.  Photographs from the outer planets had enthralled the inhabitants of this one for more than a decade, and Neptune didn’t disappoint.  Voyager 2 was able to get some great shots of the planet, including the “Great Dark Spot” which seems to have subsequently vanished. There was also time for a visit to Triton, Neptune’s volcanically active largest moon, thought to be a captured Kuiper belt object.

Neptune and Triton from the departing Voyager 2 (image credit: NASA)

Neptune and Triton from the departing Voyager 2 (image credit: NASA)

Although they didn’t know it at the time, this fly-by marked the point at which every planet in the solar system had been visited (back in the day they still had Pluto on the list).

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