Iuppiter sese obviam fecit

Yes, I know there is nothing technically interesting about yet another grainy picture of the Galilean satellites. But…

Callisto, Europa, Ganymede, Jupiter (and Io lost somewhere in transit).

…that’s taken leaning out of the kitchen window, without doing anything clever, using the battered camera I throw in my bike panniers and take to work regularly. It’s not even a very interesting camera – no fancy lenses, no high-sensitivity sensors – indeed, it’s famously terrible in low-light conditions, which I suppose by definition includes “photographing the night sky”. But all it needs is a quick crop and an inversion to show them up clearly.

The relentless march of technology has some unexpected side-effects. I don’t think I ever really though I’d be able to do this on a whim, and for all that it’s obvious it’s not difficult, it’s still a bit of a thrill.

Four hundred years ago today

7th January, 1610. Galileo turned his telescope to the sky, and “I have seen Jupiter accompanied by three fixed stars…”.

Die itaque septima Ianuarii, instantis anni millesimi sexcentesimi decimi, hora sequentis noctis prima, cum cælestia sidera per Perspicillum spectarem, Iuppiter sese obviam fecit; cumque admodum excellens mihi parassem instrumentum (quod antea ob alterius organi debilitatem minime contigerat), tres illi adstare Stellulas, exiguas quidem, veruntamen clarissimas, cognovi; quæ, licet e numero inerrantium a me crederentur, nonnullam tamen intulerunt admirationem, eo quod secundum exactam lineam rectam atque Eclipticæ parallelam dispositæ videbantur, ac cæteris magnitudine paribus splendidiores.

(I am faintly pleased that I understand more than three words of that. Life’s simple pleasures.)

Here’s where it all began, in a way. Four centuries on, we can talk quickly and happily of three-hundred-mile sulphur plumes, ice-bound planetary oceans teeming with hypothetical life, moons larger than planets, or geological features a thousand miles across; we have photographed them from near and from far, mapped them to a point, studied and speculated for lifetimes. They allowed us, less than a century later, to work out a fundamental physical constant for the first time. We have even worked with them so closely that we have begun to worry about the risk of physically contaminating them, amazing as it sounds.

But they’re still four little dots in the sky, clustered around a bigger dot; people can still pick up binoculars for the first time, or a cheap child’s telescope, look up, and feel the same rush. This is the easiest way to see it; they’re the most available sign that the system works, that there are some kind of universal laws out there, and that we ourselves can stand still and watch them played out in front of our eyes, regular as clockwork. I remember years ago, clustered in a telescope dome in a night which felt almost as cold as this one, watching the three moons strung out around Jupiter, the blurry cloud bands of light and dark on its surface… and then a perfect black circle in the middle of the southern hemisphere, as Io swung between it and the sun, letting us see an eclipse from four hundred million miles away. (We were meant to be looking at Saturn, but you don’t forget that kind of opportunity. I still have the slip of paper with the picture in a box somewhere.)

There’s a good set of posts here on the discovery and its context; if you feel up to the Latin, there’s a transcription of the Sidereus Nuncius here, or a scanned copy here (the Jovian moons are from leaf 17 on). Note the diagrams.

A new planet

It’s strange that I go on holiday and promptly fail to have enough time to do anything, but there you go. Haven’t posted in weeks.

So, moving on, today’s (yesterdays?) news. A research team in the US has identified a planet orbiting the red dwarf GJ 1214. What makes this particularly interesting – by comparison to the long line of extrasolar planets discovered in the past ten years – is two things:

  • Its characteristics. It’s quite small – six and a half earth masses, and about twice the diameter – but it’s also quite light. This indicates an unusual composition; it’s probably composed of ice and a small core, with a thick atmosphere, rather than rock. It’s hot, though – not as hot as Venus, but certainly hotter than we’d like – and so that ice is probably in some exotic form.
  • …and the way it was discovered. This wasn’t identified as the result of a high-powered orbital mission, or of extensive searching on one of the major telescopes; it was a small group of researchers, cherry-picking likely targets, for a total cost probably under half a million dollars. We can hope to see quite a few more…

We’re about four centuries – give or take three weeks – from Galileo discovering the first icy worlds, little satellites in orbit around Jupiter. This new object – a super-Ganymede as much as a super-Earth – seems a pretty triumphant discovery to mark the anniversary.