June 01 – Launch of Surveyor 1 (1966)

The Surveyors were a series of soft landing lunar probes designed to gather information about the Moon’s surface which was needed before committing to sending people up there (it would have been very embarrassing to watch a lunar module sink into the ground).  The first of these, Surveyor 1, was launched from Cape Canaveral on June 1st, 1966, using an Atlas-Centaur rocket, a modified form of the US Air Force’s Atlas ICBM.

Surveyor 1 as seen by the Lunar Reconnaissance Orbiter, 1999 (image credit: NASA)

The main scientific instruments on board were a TV camera and a “strain gauge” to measure the forces on landing.

A slightly better photograph of a Surveyor model on Earth (image credit: NASA)

There were seven Surveyors in total, with landing sites spread out across the Moon, of which numbers 2 and 4 crashed.  Surveyor 1 was sent to check out the area known as the Oceanus Procellarum (the Ocean of Storms), from where it took more than 11.000 photographs.  Procellarum is one of the lunar maria (seas), but being bigger than the rest it bears the name “ocean”.


May 30 – Discovery of Saturn’s Moon, Anthe (2007)

2007 – Saturn’s tiny (1.8km wide) moon Anthe was first spotted in Cassini images taken on May 30th, 2007, although it is now known to have been in images taken as far back as 2004.

Anthe may be part of a dynamical family with the moons Methone and Pallene. This is appropriate if true, as they were sisters in mythology, three of the Alkyonides, who threw themselves into the sea when their father was killed by Herakles.

The following photograph is the best I could find on the internet.  It bears a striking resemblance to my best efforts at capturing Venus for posterity, but I promise you it isn’t.

Anthe (image credit: NASA)

Dust from Anthe is thought to be responsible for the creation of the Anthe Ring Arc, a faint ring arc of Saturn discovered in 2007, between the Methone Ring Arc and the Pallene Ring.



January 27 – Pasiphae

Jupiter’s moon Pasiphae (known as 1908 CJ when first discovered, then Jupiter VIII) was first seen by human eyes on January 28th 1908.  The eyes in question belonged to Philibert Jacques Melotte, a British astronomer, despite the name, and the actual discovery date goes down as the 27th rather than the 28th because that was when CJ was first photographed by the Royal Greenwich Observatory.  It’s one of the retrograde satellites of Jupiter, and was eventually named after the mother of the Minotaur (a name with an “e” on the end, in the manner suggested by Jürgen Blunck to distinguish between Jupiter’s prograde and retrograde moons) after being informally known as Poseidon for a while.

There’s apparently no rush at the International Astronomical Union.  The name Pasiphae was finally proposed by the “Working Group for Planetary System Nomenclature” at the same time as eight other Jovian moons, in October 1975, 67 years after discovery.  It was then accepted by the IAU General Assembly the following August.

Daedalus and Pasiphae (fresco from Pompeii)
Daedalus and Pasiphae (fresco from Pompeii)

Pasiphae is a small moon by the standards of more well-known satellites at about 20km radius, but because of the enormous quantity of Jovian moons, most of which have radii in single figures, it’s actually one of the larger.

1904  –  Asteroid 523 Ada discovered January 29th, 1904 by American astronomer Raymond S. Dugan.  He named it after Ada Helme, a schoolfriend from Montague, Mass.

December 24 – Discovery of Saturn’s Moon, Rhea (1672)

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.

Rhea from the Cassini probe (image: NASA / JPL / SSI)
Rhea from the Cassini probe (image: NASA / JPL / SSI)

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”.

Another Rhea
Another Rhea



December 18 – Discovery of Saturn’s moon, Epimetheus (1966)

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.

Epimetheus from the Cassini Orbiter (image: NASA/JPL/SSI)
Epimetheus from the Cassini Orbiter (image: NASA/JPL/SSI)

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.

Epimetheus (3rd left) meets Pandora for the first time.
Epimetheus (3rd left) meets Pandora for the first time.

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 10B rocket.

October 25 – Discovery of Saturn’s moon, Iapetus (1671)

Iapetus, the third largest moon of Saturn, was discovered on October 25th, 1671, by Giovanni Cassini, and is a weird old place for a couple of reasons. Firstly, it looks like two different moons, depending on whether you view it from the leading or trailing hemisphere, and secondly because of a pronounced ridge around the equator that gives the moon the appearance of a walnut.
The colour difference is really obvious. It was first suggested by Cassini himself, who noticed that he could only see Iapetus when it was on Saturn’s western side. Various theories have been put forward to explain this two-tone look, with the latest being to invoke thermal segregation , as a result of Iapetus’ very long rotation period (79 Earth days). This might cause one side to be brighter than the other, with Iapetus’ tidally locked rotation being the reason it will always look darker from Earth when on one side of the planet.

Iapetus from the Cassini spacecraft (image credit: NASA)
Iapetus from the Cassini spacecraft (image credit: NASA)

The equatorial ridge has proved equally baffling, with two formation theories currently being pondered: (i) the result of much faster rotation at some point in the past, and (ii) the collapse of a ring.

Cassini view of Iapetus' equatorial ridge (image credit: NASA)
Cassini view of Iapetus’ equatorial ridge (image credit: NASA)

Iapetus was named after one of the Titans of Greek mythology, as per John Herschel’s suggestion that they be given the names of the mythological siblings of Kronos (the Greek equivalent of Saturn). Iapetus is sometimes credited with being a distant ancestor of the human race, and the story goes that each of his four sons (Atlas, Prometheus, Epimetheus and Menoetius) was responsible for a particular fault in mankind. Thanks, Iapetus.

October 24 – Discovery of Ariel and Umbriel (1851)

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.

October 10 – Discovery of Neptune’s moon, Triton (1846)

Discovered on October 10th 1846 by William Lassell, (who was living and working at that time in West Derby, Liverpool), the Solar System’s biggest retrograde moon Triton, aka Neptune I, is, at 1,353 km radius (approx) the largest satellite of Neptune.

Triton from Voyager 2 (image: NASA)
Triton from Voyager 2 (image: NASA)

Lassell wasn’t daft.  The massive Neptune itself had only been discovered 17 days previously, so where else was he going to be looking for moons?

Current thinking is that Triton is a captured Kuiper Belt Object.  It has a thin atmosphere of mostly nitrogen, with a little methane mixed in, and is, like our own Moon, locked in a synchronous orbit, meaning it always keeps the same face pointing toward its parent (or possibly in this case “adoptive parent”).

Triton (image credit: NASA/JPL-Caltech)
Triton (image credit: NASA/JPL-Caltech)


1868  –  Discovery of asteroid 106 Dione by J C Watson.

1874  –  Discovery of asteroid 139 Juewa, also by J C Watson.

October 04 – Launch of Luna 3 (1959)

Exactly two years after the international frenzy surrounding their first Sputnik, the Soviet Union pulled off another coup with Luna 3, launched on October 4th, 1959, to send back the first photographs of the far side of the Moon.

Now by 21st century standards, the image quality was not great, and if you gave me a mouldy orange and a piece of sandpaper I could probably get a similar result.  But back then it was a startling technological achievement, and more importantly, something the Americans hadn’t done yet.

After its launch from the Baikonur Cosmodrome,  Luna 3 reached as close as 6,200 km of the lunar surface, and took a total of 29 photographs before heading back towards Earth. As there was no chance of recovering the probe, the plan was to transmit these photographs electronically to Soviet ground stations. This was only partly sucessful because the craft had a lower than expected signal strength, but about half the pictures were eventually retrieved before contact was lost on October 22nd.

Soviet postage stamp commemorating the start of far-side photography on October 7th.



September 30 – Discovery of Jupiter’s Moon, Themisto (1975)

The Jovian moon Themisto, discovered on September 30th 1975 by Charles Kowal and Elizabeth Roemer, is a rather small, irregular moon, orbiting about halfway between Jupiter’s large, well known Galilean moons and the rather less famous Himalia Group of prograde irregular companions. The best photographs currently available on the Internet show Themisto as a white pinhead on a black background, so I haven’t bothered “borrowing” one.

Themisto was named after a character from Greek mythology, the subject of a tragedy by Euripides which has unfortunately been lost. In the play, Themisto accidentally kills her own children, believing them to be the offspring of her husband’s first wife. When she realises what has happened, Themisto does what the star of any tragedy would be expected to do, and kills herself as well. The Greek stage at an average drama festival was littered with more bodies than an entire season of Murder She Wrote.

Co-discoverer Elizabeth Roemer also has two asteroids to her name, the magnificently named 1930 Lucifer and 1983 Bok. Charles T Kowal does even better, with 19 minor planets discovered between 1970 and 1981, including 2060 Chiron, the first of the centaurs. His collection of astronomical trophies also boasts a few comets, and Leda, another Jovian satellite.