As I posted a little earlier on The Guardian:

Desperately sad news.

His contemporary and science fiction novels have been an important part of my life for many, many years, and I shall miss knowing that his twisted and brilliant imagination is beavering away at new works.

But if nothing else, looking for a silver lining to this dark, dark cloud, I'm at least happy to have the chance to thank him publicly, before he's gone, for the great pleasure I've had in reading his books.

I'm sure he's greatly loved by many and I hope that that knowledge can go at least some small way to helping him and his wife through the months to come.

Problem is that Herschel's primary mirror was only polished to the level of surface roughness required for the telescope to be diffraction-limited (i.e. as good as it gets) at far-infrared wavelengths. It wasn't polished to the level necessary to form good images at optical wavelengths.

Just to put some numbers on that, Herschel's shortest operating wavelength is 70 microns (70 millionths of a metre), whereas the red end of the visible is around 0.7 microns, i.e. 100 times shorter.

Polishing the mirror to a factor of 100 lower surface roughness would have been far more expensive and perhaps even not possible using the underlying segmented silicon carbide technology. (SiC can be polished to optical tolerances, but I don't know if Herschel's substrate was made to the appropriate tolerances).

Space isn't really cold, not at least when you're close to a star like the Sun. After all, the Earth's isn't cold (well, relatively speaking), despite the fact that it sits in space. Sure, there's some internal heating from our molten core and some greenhouse effect from our atmosphere, but the underlying reason that the Earth is warm (again, relatively speaking) is because it's in thermal equilibrium with sunlight at a distance of 150 million kilometres from the Sun.

So if you stick something in space at L2, it's essentially at the same distance from the Sun as the Earth and thus, roughly speaking, it'll end up at the same temperature as the Earth.

The big difference, however, is that there's no atmosphere to transport heat by conduction or convection, so the side of the object that's facing the Sun will get hot and the other side, in the shade, will be colder. Of course, conduction by the object itself can transport heat from the hot side to the cold side, evening things out a bit. But if you can thermally isolate one side from the other, the side facing away from the Sun can get really, really cold, as it radiates any excess heat into the 3K "heat sink" of the Universe.

Which is exactly what spacecraft at L2 do. They have a hot side, facing the Sun and Earth, generating power to run the satellite and to communicate data back to Earth. Then they have a cold side, separated from the hot side by a sunshield and facing out into space, which can then get very, very cold, provided the two sides are thermally decoupled. You stick your telescope and instruments on that side and you can get nice and chilly.

(That said, you can only reach about 30–50K or so, which is fine for near-infrared observatories and their instruments, but the instruments used by far-infrared and sub-millimetre observatories need to be much colder, down around absolute zero, in order that their detectors don't blind themselves. That's why Herschel has liquid helium and why it will go blind when it runs out. Being at L2 is only half the story for Herschel.)

The beauty of L2 is that you keep the Sun, the Earth, and the Moon shining permanently on one side of the spacecraft, but never on the other side, if designed well. Spacecraft like Hubble in low-Earth orbit have to contend with half the sky being permanently filled with a big hot object called the Earth, and as you go around in orbit, the combined Earth and Sun illumination is constantly changing: not a good place to get a spacecraft really cold.

It's not being moved because it will clutter up L2. Indeed, such satellites don't sit exactly at the L2 point, but travel around it in orbits which are hundreds of thousands of kilometres wide. There's effectively no danger of any satellites at L2 hitting future ones.

No, the reason is that L2 isn't a stable location: the gravitational potential there is saddle-shaped. Very crudely, along the line of the orbit around the Sun, the satellite sits at the bottom of a curve. Move forward a bit and the Earth's gravity pulls you back. Fall behind a little bit and the same happens. However, perpendicular to the orbital track, in the plane of the ecliptic (the plane containing the planets), it's more like the top of a gravitational hill. Fall a little away from the Earth and bingo, the Earth is no longer strong enough to pull you back and you fall off, outwards.

But if you fall inwards, towards the Earth, the Earth's gravity gets stronger and pulls you even closer. So much so, that you might end up hitting the Earth.

So that's the reason why Herschel and other satellites there (WMAP in the past, Planck today, Gaia and JWST in the future) are pushed off L2 while the satellites still have propellant and are functional (if not scientifically) into heliocentric orbits, to prevent the possibility of the falling onto the Earth in an uncontrolled manner later.

is the same as the AC who then posted this one:

then I'd say that's exactly what you did say.

And as for your assumption that I'm an American ... well, you haven't got a clue, mate. You're many thousands of kilometres off. There are other countries in the world where English is the native language, after all. "We have 2013" indeed.

Sometimes I really do wonder whether /. is worth the trouble.

Err, of course the sky is blue under moonlight: it's just reflected sunlight, after all (but see below).

The problem is that the Moon is much fainter than the Sun and thus the overall light level is low. So low that it doesn't significantly activate the colour-sensitive cones in the human eye, meaning that you only really see with the rods in black-and-white.

But take a long exposure with a camera (or a video frame rate with this Canon sensor), and the blue will most definitely come through.

(Actually, the moonlight-illuminated sky is slightly bluer than a sunlight-illuminated one, as the Moon's slightly brown-ish colour first imprints its spectral dependence on the sunlight which bounces off it. That light is then Rayleigh-scattered off the molecules in the Earth's atmosphere, imprinting the well-known 1/lambda^4 dependence which makes the sky blue).

My thought entirely: it was in use as a scientific laboratory for many, many years prior to 2001 by Raymond Davis, Jr and colleagues to detect solar neutrinos. He identified a significant deficit in the number of neutrinos detected with respect to predictions and worked with John Bahcall for many years to demonstrate that his experiment was working correctly and the standard solar neutrino model was correct. Nevertheless, people doubted them for many years.

Later however, the Sudbury Neutrino Observatory in Canada and other experiments demonstrated that some of the electron neutrinos created in the Sun were mutating into muon and tau neutrinos (via "neutrino oscillation") en-route from the Sun to the Earth, providing an explanation for why Davis (whose experiment was only sensitive to electron neutrinos) was detecting only a third or so of the number predicted by the standard solar model.

Vindicated, Davis was then awarded part of the Nobel Prize for Physics in 2002, although unfortunately, Bahcall was not similarly rewarded. Neutrino oscillation and the direct implication that neutrinos have mass are profound discoveries, since they are inconsistent with the current Standard Model of particle physics. Many physicists are now working on further experiments and theory in this area.

I have had custom silicone moulds for my earphones for almost 10 years and it was one of the best investments I've ever made. The earphones are Etymotic ER4P's and the moulds were made by the Dutch company, Elacin, following the traditional route, i.e. having deep canal impressions made by an audiologist. Elacin work closely with Etymotic, so made moulds to specifically fit their earphones: while I don't see this particular service offered on their website anymore, my experience with them was that they're happy to talk to customers and do what's necessary.

The fit is of these moulds is perfect, the external sound suppression impressive, and the internal sound spectacular, thanks of course to the ER4P's. Together, this means I can listen to and enjoy music at low volumes, and for people around me, they hear absolutely no spillover.

Sure, the combined cost was daunting at the time: somewhere around €600. Ouch. But amortised out over 10 years already and potentially many years to come, it has been well worthwhile for the quality of the sound and the sealing off of the outside world when desired. Living in Holland with all its off-road, dedicated cycling paths, I can even make good use of them on my daily commute.

If I had one complaint about them, it'd be the way that the piezo drivers of the Ety's protrude, making it impossible to place your ear on a pillow with the earphones in. I fly a lot and would like to be able to sleep with the earphones in, suppressing sound and perhaps playing something ambient.Perhaps I should splash out again and get something like high-end Ultimate Ears earphones, where the custom moulds and electronics are integrated into a "flatter" package ... ;-)

I realise that the title of this article was carried over from the CBC article, but could we at least try to remember that it's astronomers that discover things like this high-redshift galaxy, not an administration like NASA in isolation? I don't mean to diminish the absolutely central role played by NASA in both Hubble and Spitzer, of course, but at the same time, a whole range of people, institutions, and organisations come together to make scientific discoveries like this possible, and I think it's important that we recognise that science is often a highly collaborative and international endeavour.

For example, there are 23 astronomers who co-authored the paper on this galaxy: 11 are from US institutions, 11 from European institutions, and 1 from a Chinese one. Note, I didn't say that they were (necessarily) American, European, and Chinese: in the list of co-authors, there are at least some Europeans working in the US and vice versa.

Also, the Hubble Space Telescope is a collaboration between NASA and ESA, the European Space Agency, albeit with NASA in this instance contributing the majority. There are other space missions including Herschel and Planck which are led by ESA, but in which NASA plays a minority role. Many space missions are collaborative in this way, in essence underpinning the mix of US-based, Europe-based, and other international astronomers who've written this paper.

In more detail, it can get even more complicated when you realise that NASA, ESA, and other space agencies themselves employ astronomers and other space scientists, so in that sense, discoveries can be made by those organisations too.

Speaking of which, it might have been more appropriate to give the links to the original US and European press releases from the Space Telescope Science Institute, NASA, and ESA to get the full story.

Anyway, despite the (important, I believe) pedantry, this is is an interesting discovery :-)

Sorry, you're both correct: to say that we "know" was perhaps too strong a statement on my part. It was just meant as a scientific shorthand for "some smart folks really really think they came from Mars and they have some really strong arguments (and data) to support that claim", as you wrote.

It might have been better to say something like it is strongly believed that, or it is very likely that, or the most likely interpretation is that, or there is a very strong case for, and so on. But it's a pretty common shorthand in science to say "we know", and everybody understanding what is meant by such a statement without delving into the deeper recesses of epistemology.

In answer to the point made that "we were never there", err, where? Mars? No, we, as people, were not; but we, via some pretty capable robots, were. One of the fundamental pieces of evidence that scientists use to justify the claim that we have Mars rocks on Earth is that trapped gases in them have an isotopic ratio that matches that of the Martian atmosphere as measured by Viking, not that of Earth.

Absolutely, positively? No, science doesn't deal in those statements. Based on all available evidence, so likely that it's perfectly reasonable to effectively rule out nuttier alternatives? Yes.

Well, in principle the paper is a fairly simple series of mathematical equations which you could actually work out on the back of an envelope. The devil though is in the details, namely the numerical parameters input to those equations. While many of those are straightforward and well-known, some may enter that category of WAGs (wild-assed guesses), and it's quite possible that the equations are particularly sensitive to (some of) those. That's why it's worth reading, to try and figure out where the issues may be.

As for the testability side, you're right, of course: very hard. But again, since we know of Martian rocks having made it to Earth via this mechanism, we can at least start to use some hard numbers based on that to try and constrain the likelihood of the Earth rocks having made it to other planets / moons.

I've made a quick scan of the underlying academic article by Hara et al., along with one of my colleagues in a meeting here, who is closely involved in the issue of planetary protection (i.e. making sure that our spacecraft don't "pollute" the solar system bodies they fly to and land on).

Of course, this is a known issue in general: after all, there are meteorites on Earth which we know came from Mars, so the converse is obviously possible. But extending this to moons of Jupiter, Kuiper Belt objects, and even exoplanetary systems, and finding that a significant number of Earth rocks may have been dumped there is interesting. So, the article is worth a more careful read.

However, my antennae were sent into a state of high agitation when I saw that the article has been posted on the arXiV following its having been accepted to the infamous Journal of Cosmology. We've discussed that here before: I invite you to view the journal website (easily found by googling) and decide for yourselves how reputable it is.

Which raises the question of why Hara et al. chose to publish there. That I can't answer, obviously, but will keep it firmly in mind as I read the paper in more detail.

The squirrels in question aren't the grey or red ones that run around in trees; they're ground squirrels, so things like marmots and prairie dogs at the big end and chipmunks at the small end.

I don't think regular grey tree squirrels are from the same genus. And I'm not 100% sure that all ground squirrels do this; the classic example of an infrared light sabre wielding species is the California ground squirrel.