I’ll keep this quick, but as you may have heard,July 16th 1969 is a fairly important day in spaceflight history. It’s the day on which Neil A Armstrong, Michael Collins and Edwin “Buzz” Aldrin decided to get away from it all. Their Saturn V rocket (SA-506), the fifth manned Apollo mission, blasted off from the Kennedy Space Centre at about half past one in the afternoon (Staffordshire Time) and may be the reason I have the vaguest recollection of my infant school gathering after dinner to watch a launch on the school television.
So it’s 2019, and 50 years since the launch, and the media is abuzz with stuff about every tiniest aspect of the mission, so I’m not going to try to compete.
Also today, in 1990, Mark R Showalter, using old frames from Voyager 2, discovered Saturn’s walnut-shaped moon, Pan, in the Encke Gap of the A Ring (the outermost of the main bright rings).
Thanks to the Cassini probe, we now have images beyond the wildest dreams of Voyager scientists:
Pan, of course, invented the pan pipes. He was a pretty hot musician all round, but a little big-headed. The story goes that he challenged Apollo to a musical duel. Pan was good, but Apollo was better. Only one person listening to the contest believed that Pan had won. This was Midas (he of the golden touch). So annoyed was Apollo at this lack of musical taste that he changed Midas’ ears into something more appropriate: those of a donkey.
Now, correct me if I’m incorrect, but in today’s artistic offering, is Pan playing his own invention upside-down?
This post originally published in 2015. Updated 2017, and again in 2019.
Today’s anniversary is the discovery of Neptune‘s second largest moon, Proteus, found by analysis of Voyager 2 snapshots taken over a period of time leading up to June 16th 1989. So, while June 16th isn’t the actual discovery date, it’s as close as we’re likely to get. It is thought that Proteus wasn’t formed at the same time as Neptune, but is a by-product of the capture of Triton.
Proteus is approximately 418 km in diameter (about 260 miles) and orbits Neptune close to the equatorial plane at a distance of a little over 117,000 km. But aside from this, and the fact that it is dark and heavily cratered, almost nothing else is known about it.
Proteus is named after a shape-changing sea god, son of Poseidon, the Greek god whose Roman equivalent is Neptune. Neptune’s moons are generally named after children or other associates of Poseidon (Triton, for example, was his other son).
Today in 2004, two new moons were discovered around Saturn by the Cassini Imaging Team at NASA. They are now named Methone and Pallene, in keeping with John Herschel’s suggestion that Saturnian moons should be named after the close family members of Kronos (the Greek equivalent to the Roman Saturn).
Methone is really small. It’s about two miles (3 km) in diameter, and orbits every 24 hours, over 120,000 miles above the planet, between the orbits of Mimas and Enceladus, and may well have been part of one of them at some time in the past.
Pallene is also diminutive, but at three miles wide (4 km) it is the larger of the Alkyonides group comprising itself, Methone and Anthe(the smallest).
1966 – Launch of Surveyor 1, on its way to the Oceanus Procellarum (Ocean of Storms) to check out the Moon’s surface prior to the launch of the Apollo program.
1990 – Launch of the ROSAT (Röntgensatellit) x-ray and UV telescope from Cape Canaveral.
Today’s main event is not dissimilar to yesterday’s. It happened in 1764, and was the discovery of a globular cluster, Messier 12, (or NGC 6218), by Charles Messier, one day after he discovered globular cluster M10. And at a casual glance, the photograph I’m using today looks remarkably similar to the one I used yesterday. But I’ve had a close look, and they definitely two different balls of stars.
M12 is approximately 75 light years across, at a distance from Earth of about 15,700 light years. It can be located as a faint fuzz in the constellation Ophiuchus with good binoculars, but needs a fairly hefty telescope to bring out detail.
I suppose the obvious question, with M10 on the 29th of May and M12 on the 30th is: what about Messier 11? Unfortunately for Charles M11 had already been discovered. He included it in his catalogue, but German astronomer Gottfired Kirch beat him to it by a mere 63 years. M11 is in the constellation of Scutum (the shield), and is commonly known as the “Wild Duck Cluster”.
Extrasolar planet MOA-2007-BLG-192Lb (or just MOA-192b to its friends) was discovered orbiting the low mass red dwarf of the same name (but without the “b”) on May 30, 2008. Spotted by the MOA-II gravitational microlensing survey, it is one of the smaller known extrasolar planets (about 3 times the mass of Earth) and has an appropriately tiny parent star of about 6% the size of the Sun.
1903 – Asteroid 511 Davida discovered in 1903 by R S Dugan and named after astronomer David Peck Todd.
2007 – Saturn’s tiny moon Anthe was first spotted in Cassini images. 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.
1963 – Happy birthday Helen Sharman, OBE, Sheffield native, chocolate chemist and first Briton in space. She flew on Soyuz flight TM-12 to the Mir space station. It was her only mission.
March 17th 1930: astronaut Colonel James Benson Irwin, USAF, born in Pittsburgh PA.
In 1971 Irwin, Apollo 15 lunar module pilot, became the eighth man to walk on the Moon, spending over 18 hours on the surface. He also, on his return, became one of the first people to be grounded, quite literally, for smuggling postage stamps into space.
1852 – Asteroid 16 Psychewasdiscovered on March 17th 1852 by Annibale de Gasparis. Psyche is a large asteroid, about 200 km in diameter, accounting for about 1% of the mass of the entire asteroid belt. It’s an M-type asteroid, probably mostly nickel and iron.
Psyche is named for a mythological princess, who caught the eye of the god Cupid. The story is told by Lucius Apuleius in The Golden Ass.
In early 2017 NASA announced plans to send a probe to Psyche in 2023, as part of their Discovery Program, the main reason being that, as a metallic asteroid, it represents one of the few classes of objects in our neighbourhood that haven’t yet been visited.
1899 – Saturn’s moon Phoebediscovered by American astronomer W H Pickering. It, too, is about 200 km in diameter, and may be a captured centaur from the Kuiper belt. We have some spectacular photographs of Phoebe following the visit of the Cassini spacecraft in 2004.
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.
J R Hind discovered today’s main belt asteroid, 23 Thalia, from Hyde Park, London, on December 15th, 1852 (I’d like to see him try that nowadays). Thalia is an S-type asteroid of about 107 km diameter, located between the 3:1 and 5:2 Kirkwood gaps.
In Greek mythology, Thalia, daughter of Zeus and Mnemosyne, with a name derived from the verb “to flourish”, was the muse of comedy and pastoral poetry. She may or may not (depending on which source you believe) have been the mother of the Corybantes, attendants to the Great Mother of the Gods, and associated with particularly orgiastic rites.
We also have a moon today. The discovery of Janus, one of the inner Saturnian satellites, is attributed to Audouin Dollfus, who first observed it on December 15th 1966. Three days later, Richard Walker also observed an object in the right place but at the wrong time, which caused confusion for a while, but was eventually found to be another moon, Epimetheus, which shares an orbit with Janus.
Janus is the two-faced Roman god of beginnings, entrances, gates, doors, etc. You should thank him the next time an automatic door opens for you. Janus is also one of the select group of deities after whom a month (January) is named, and strangely he has no Greek counterpart.
1965 – launch of San Marco 1 by Italy. Being their first satellite, the Italians wisely did not fill it with lots of expensive equipment. It did, though, contain a couple of experiments to study the ionosphere, the layer of the atmosphere stretching from about 60 km to 1,000 km, a region you need to know about if you’re planning to become a space-faring nation, needing to send radio messages over great distances.
2000 – Death of George Alcock, aged 88, hunter of novae and comets. I believe he found five of each (remarkable for south-eastern England), some of them from indoors using binoculars, and even occasionally through double glazing1! His eyesight must have been unbelievable.
2014 – Voyager 1 crossed the termination shock.
2015 – Launch of Expedition 46 to the International Space Station. This caused considerable press interest in my homeland (in fact I’m going to call it a frenzy) because in addition to Russian cosmonaut Yuri Malenchenko and American astronaut Tim Kopra, the three-man crew contained Tim Peake, the first Briton to float into the ISS (I was going to say “set foot aboard” the ISS, but I’ve seen the footage, and feet don’t feature much). Because of the numbering system they use at the ISS when crews overlap, these three also formed part of Expedition 47.
As a supporter of Port Vale FC, I was distraught to discover that one of Tim Peake’s tasks whilst on this mission was to unveil a flag featuring the name of our local rivals, Stoke City. I’ve gone off him a little.
1 Journal of the British Astronomical Association, vol.111, no.2, p.64-66
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.
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.
Iapetus was named after one of the Titans, as per John Herschel’s suggestion that they be given the names of the mythological siblings of Kronos (the Greek equivalent of Saturn).
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.
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.
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, Polydeucesby the Cassini Imaging Science team.