Archive for supernova

Ligatures, Diphthongs and Supernovae

Posted in History, Pedantry, The Universe and Stuff with tags , , , , , , , , on January 18, 2016 by telescoper

At the weekend I noticed a nice article by John Butterworth on his Grauniad blog about where Gold comes from. Regular readers of this blog (Sid and Doris Bonkers) know that I am not at all pedantic but my attention was drawn to the plural of supernova in the preamble:

Supernovas

I have to confess that I much prefer the latin plural “supernovae” to the modernised “supernovas”, although most dictionaries (including the One True Chambers) give these both as valid forms.  In the interest of full disclosure I will point out that I did five years of Latin at school, and very much enjoyed it…

When I tweeted about my dislike for supernovas and preference for supernovae some replied that English words should have English plurals so that supernovas was preferred (although I wonder if that logic extends to, e.g. datums and phenomenons). Others said that supernovae was fine among experts but for science communication purposes it was better to say “supernovas” as this more obviously means “more than one supernova”. That’s a reasonable argument, but I have to admit I find it a little condescending to assume that an audience can cope with the idea of a massive star exploding as a consequence of gravitational collapse but be utterly bewildered by a straightforward latin plural.

One of the reasons I prefer the Latin plural – along with some other forms that may appear archaic, e.g. Nebulae – is that Astronomy is unique among sciences for having such a long history. Many astronomical terms derive from very ancient sources and in my view we should celebrate this fact because it’s part of the subject’s fascination. That’s just my opinion, of course. You are welcome to disagree with that too.

Anyway, you might be interested to know a couple of things. One is that the first use of “super-nova” recorded in the Oxford English Dictionary was in 1932 in a paper by Swedish astronomer Knut Lundmark. This word is however formed from “nova” (which means “new” in Latin) and the first use of this term in an astronomical setting was in a book by Tycho Brahe, published in 1573:

Brahe_book(I’ll leave it as an exercise to the student to translate the full title.)

Nowadays a nova is taken to be a much lower budget feature than a supernova but the “nova” described in Tycho’s book was was actually a supernova, SN1572 which he, along with many others, had observed the previous year. Historical novae were very often supernovae, in fact, because they are much brighter than mere novae. The real difference between these two classes of object wasn’t understood until the 20th Century, however, which is why the term supernova was coined much later than nova.

Anyway, back to pedantry.

A subsequent tweet from Roberto Trotta asserted  that in fact supernovae and supernovas are both wrong; the correct plural should be supernovæ, in which the two letters of the digraph “ae” are replaced with a single glyph known as a ligature. Often, as in this case, a ligature stands for a diphthong, a sort of composite vowel sound made by running two vowels together.   It’s one of the peculiarities of English that there are only five vowels, but these can represent quite different sounds depending on the context (and on the regional accent). This  means that English has many hidden diphthongs. For example,  the “o” in “no” is a diphthong in English. In languages such as Italian, in which the vowels are very pure, “no” is pronounced quite differently from English. The best test of whether a vowel is pure or not is whether your mouth changes shape as you pronounce it: your mouth moves as you say an English “no”, closing the vowel that stays open in the Italian “no”…

So, not all diphthongs are represented by ligatures. It’s also the case that not all ligatures represent diphthongs. Indeed some are composed entirely of consonants. My current employer’s logo features a ligature formed from the letters U and S:

image

The use of the ligature æ arose in Mediaeval Latin (or should I say Mediæval?). In fact if you look at the frontispiece of the Brahe book shown above you will see a number of examples of it in its upper-case form Æ. I’m by no means an expert in such things but my guess is that the use of such ligatures in printed works was favoured simply to speed up the typesetting process – which was very primitive – by allowing the compositor to use a single piece of type to set two characters. However, it does appear in handwritten documents e.g. in Old English, long before printing was invented so easier typesetting doesn’t explain it all.

Use of the specific ligature in question caught on particularly well in Scandinavia where it eventually became promoted to a letter in its own right (“aesc”) and is listed as a separate vowel in the modern Danish and Norwegian alphabets.  Early word-processing and computer typesetting software generally couldn’t render ligatures because they were just too complicated, so their use fell out of favour in the Eighties, though there are significant exceptions to this rule. Latex, for example, always allowed ligatures to be created quite easily. Software – even Microsoft Word – is much more sophisticated than it used to be, so it’s now not so much of a problem to use ligatures in digital text. Maybe they will make a comeback!

Anyway, the use of æ was optional even in Mediaeval Latin so I don’t think it can be argued that supernovæ is really more correct than supernovae, though to go back to a point I made earlier, I do admit that a rambling discussion of ligatures and diphthongs would not add much to a public lecture on exploding stars.

 

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Four Times a Supernova

Posted in The Universe and Stuff with tags , , , , on March 9, 2015 by telescoper

I’ve been a bit pressed for time recently (to put it mildly) so am a bit late catching up on a wonderful observation (by Kelly et al.) reported in last week’s issue of Science. Here’s the abstract:

In 1964, Refsdal hypothesized that a supernova whose light traversed multiple paths around a strong gravitational lens could be used to measure the rate of cosmic expansion. We report the discovery of such a system. In Hubble Space Telescope imaging, we have found four images of a single supernova forming an Einstein cross configuration around a redshift z = 0.54 elliptical galaxy in the MACS J1149.6+2223 cluster. The cluster’s gravitational potential also creates multiple images of the z = 1.49 spiral supernova host galaxy, and a future appearance of the supernova elsewhere in the cluster field is expected. The magnifications and staggered arrivals of the supernova images probe the cosmic expansion rate, as well as the distribution of matter in the galaxy and cluster lenses.

And here’s a nice picture of the system which I ripped of from a nice report in Physics World:

PW-2015-03-05-Commissariat-supernovae

Multiple images of background objects caused by gravitational lensing have been observed before, but the key thing about this particular “Einstein Cross” is that the background object is a type of exploding star called a supernova. That means that the light it emits will decay over time. That light reaches us via four different paths around the intervening galaxy cluster so monitoring the different evolution in the four images will yield direct measurements of the physical scale of the cluster and hopefully  answer a host of interesting cosmological questions.

Do-It-Yourself Supernova Explosion

Posted in Education, The Universe and Stuff with tags , , , , on August 15, 2014 by telescoper

Visitors to the office of the Head of the School of Mathematical and Physical Sciences at the University of Sussex often remark upon the presence of these two objects and inquire as to their purpose:

Supernova

Since I don’t play golf and am a bit long in the tooth to be a fan of Peppa Pig, most assume that it must be for some strange astrophysical reason. I tried asking on Twitter what people think I use them for, and the most common answer was to demonstrate the relative size of the Earth and Moon. As Roy Walker would have said, “That’s a good answer, but it’s wrong”.

In fact I use the objects concerned to demonstrate what goes on when a star goes supernova.

The point is that a supernova explosion begins with gravitational collapse of the progenitor star, so why does that manifest itself as an explosion? The point is that the outer layers are blown off while the core collapses into a compact object such as a neutron star or, perhaps, a black hole.

The way to demonstrate this is first to balance the golf ball (representing the outer layers) on top of the beach ball; the air hole in the latter is a useful place to do this. You then lift the conjoined objects to a reasonable height and drop them onto the table or bench provided for such a purpose in a lecture theatre. The objects fall together under gravity until the beach ball hits the surface. You will find that the beach ball (representing the core) stops still while the golf ball (representing the outer shells) shoots upwards as most of the kinetic energy of the system is transferred to it during the bounce.

I think this is quite an effective demonstration, but I’d encourage inexperienced lecturers to note that there is a Health and Safety Issue, so it is necessary to carry out a risk assessment before attempting it. When I first did this during a lecture many years ago, I used a ball bearing rather than a golf ball and a fully-inflated and much larger beach ball instead of the more manageable (and slightly deflated) Peppa Pig one I now use. I told the students in the audience to watch carefully what happened and then dropped them as described above…

What happened in that case was that the ball bearing rocketed up so fast that it reached the ceiling and smashed into the lights above the lecturer’s bench, whereupon there was a very loud bang and I was showered with broken glass and other debris. I have to say that got the loudest round of applause I’ve ever had while lecturing, but it wasn’t exactly the effect I’d been hoping for.

But the real reason for posting today is to wish a very happy 65th birthday to supernova expert extraordinaire and occasional reader of this blog, Robert Kirshner of Harvard University, who has celebrating along with a number of my astro-chums at a conference in Australia.

Many happy returns, Bob!

Hot News! Supernova in M82

Posted in The Universe and Stuff with tags , , , , , on January 22, 2014 by telescoper

Very exciting news today – a supernova has gone off in Messier 82. In fact, according to this sequence of images from Japan it actually started to brighten about a week ago:

psn-m82

Being arranged in Japanese fashion, you have to read these from top to bottom but starting at the right, so the supernova can be seen to be steadily brightening, i.e. decreasing in magnitude from 17.0 to 11.9. That means it’s now visible with binoculars and will have been seen already by many amateur astronomers. The exciting question this time is whether we’ll get any neutrinos from it!

UPDATE: I’m told that, close as it is, M82 is probably too far to detect neutrinos. Boo.

This is the nearest supernova since 1987a which was observed in, er, 1987. This is the nearest Type Ia supernova for a very long time (possibly 1937), so it’s of considerable interest for the use of such objects in cosmology. There have been other close ones since the nearest one I can remember, 1987a, which was observed in, er, 1987 but all have been Type II.

UPDATE: Thanks for the people who pointed out my error which I’ve left in to show that I don’t know much about supernovae so you shouldn’t phone me up to ask.