Posted in Biographical with tags Blogs on September 15, 2016 by telescoper
When I logged onto WordPress today I received a message that it was the 8th anniversary of my registration with them as a blogger, which is when I took my first step into the blogosphere; that was way back on 15th September 2008. I actually wrote my first post that day too. Unfortunately I didn’t really know what I was doing on my first day at blogging – no change there, then – and I didn’t actually manage to figure out how to publish this earth-shattering piece. It was only after I’d written my second post that I realized that the first one wasn’t actually visible to the general public because I hadn’t pressed the right buttons, so the two appear in the wrong order in my archive.
I’d like to take this opportunity to send my best wishes, and to thank, everyone who reads this blog, however occasionally. According to the WordPress stats, I’ve got readers from all round the world, including one in the Vatican! If you’re interested in statistics then, as of 14.00 BST today, I have published 3,343 blog posts, and have received 2,853,105 hits altogether; I get an average of about 1200 per day, but this varies in a very erratic fashion. The greatest number of hits I have received in a day is 8,864 (at the peak of the BICEP2 controversy). There have been 24,907 comments published on here and 1,556,259 rejected. Most of the rejected comments were from automated spam bots, but a small number have been removed for various violations, usually for abuse of some kind. Yes, I do get to decide what is published. It’s my blog!
While I am on the subject of comments, I’ll just repeat here my comments policy as stated on the home page of this blog:
Feel free to comment on any of the posts on this blog but comments may be moderated; anonymous comments and any considered by me to be abusive will not be accepted. I do not necessarily endorse, support, sanction, encourage, verify or agree with the opinions or statements of any information or other content in the comments on this site and do not in any way guarantee their accuracy or reliability.
It does mean a lot to me to know that there are people who find my ramblings interesting enough to look at, and sometimes even to come back for more, so I’d like to take this opportunity to send my best wishes to all those who follow this blog and especially those who take the trouble to comment on it in such interesting and unpredictable ways!
Just a year ago today, after travelling some 1.4 billion years, the gravitational wave chirp we christened GW150914 passed through Earth. It disturbed the two gravitational wave detectors of the LIGO observatory enough for us to notice it, to get excited about it, and to get a large fraction of the general public excited about it! But GW150914 just kept on going and is now one further year along in its journey through the Universe. And it will keep going, spreading out and getting weaker but not otherwise being much disturbed, forever. Literally forever.
And GW150914 hardly noticed us! When we observe the Universe with our telescopes, detecting light or radio waves or gamma rays from the enormous variety of luminous objects out there, we capture the energy that enters our telescopes. The photons from a distant star terminate their journeys in our telescopes, leaving a tiny hole in the…
After today’s first release of data by the Gaia Mission, as a service to the community, for the edification of the public at large, and by popular demand, here is a list of Top Ten Gaia Facts.
Gaia looks nothing like the Herschel Space Observatory shown here.
The correct pronunciation of GAIA is as in “gayer”. Please bear this in mind when reading any press articles about the mission.
The GAIA spacecraft will orbit the Sun at the Second Lagrange Point, the only place in the Solar System where the effects of cuts in the UK science budget can not be felt.
The data processing challenges posed by GAIA are immense; the billions of astrometric measurements resulting from the mission will be analysed using the world’s biggest Excel Spreadsheet.
To provide secure backup storage of the complete GAIA data set, the European Space Agency has commandeered the world’s entire stock of 3½ inch floppy disks.
As well as measuring billions of star positions and velocities, GAIA is expected to discover thousands of new asteroids and the hiding place of Lord Lucan.
GAIA can measure star positions to an accuracy of a few microarcseconds. That’s the angle subtended by a single pubic hair at a distance of 1000km.
The precursor to GAIA was a satellite called Hipparcos, which is not how you spell Hipparchus.
The BBC will be shortly be broadcasting a new 26-part TV series about GAIA. Entitled WOW! Gaia! That’s Soo Amaazing… it will be presented by Britain’s leading expert on astrometry, Professor Brian Cox.
It seems like only yesterday that I was blogging excitedly about the imminent launch of the European Space Agency’s Gaia Mission. In fact it was almost three years ago – 1000 days to be precise – and today the world of astronomy is a-flutter with excitement because we’ve just seen the first release of data from the mission. You can find an overview with links to all the yummy data here. I can’t resist pointing out the adoption of a rigorously Bayesian method for dealing with partial or incomplete data when a full astrometric solution is not possible due to insufficient observations. If you want to go straight to the data archive you go here or you could try one of the other data centres listed here. It’s great that all this data is being made freely available, but this is only the first set of data. It’s just a hint of what the mission overall will achieve.
If you would prefer some less technical background to the mission have a look here.
Here’s a summary (courtesy of ESA) of what Gaia has achieved so far:
There’s much more to Gaia than pictures, but here’s the first map of the sky it produced:
I remember first hearing about Gaia about 15 years ago when I was on a PPARC advisory panel and was immediately amazed by the ambition of its objectives. As I mentioned above, Gaia is a global space astrometry mission, which will make the largest, most precise three-dimensional map of our Galaxy by surveying more than a billion stars; DR1 is really just a taster as the measurements will become more complete and more accurate as the mission continues.
In some sense Gaia is the descendant of the Hipparcos mission launched in 1989, but it’s very much more than that. Gaia monitors each of its target stars about 70 times over a five-year period. It is expected to discover hundreds of thousands of new celestial objects, such as extra-solar planets and brown dwarfs, and observe hundreds of thousands of asteroids within our own Solar System. The mission is also expected to yield a wide variety of other benefits, including new tests of the General Theory of Relativity.
Gaia will created an extraordinarily precise three-dimensional map of more than a thousand million stars throughout our Galaxy (The Milky Way) and beyond, mapping their motion, luminosity, temperature and chemical composition as well as any changes in such properties. This huge stellar census will provide the data needed to tackle an enormous range of important problems related to the origin, structure and evolutionary history of our Galaxy. Gaia will do all this by repeatedly measuring the positions of all objects down to an apparent magnitude of 20. A billion stars is about 1% of the entire stellar population of the Milky Way.
For the brighter objects, i.e. those brighter than magnitude 15, Gaia measures their positions to an accuracy of 24 microarcseconds, comparable to measuring the diameter of a human hair at a distance of 1000 km. Distances of relatively nearby stars are measured to an accuracy of 0.001%. Even stars near the Galactic Centre, some 30,000 light-years away, have their distances measured to within an accuracy of 20%.
It’s an astonishing mission that will leave an unbelievably rich legacy not only for the astronomers working on the front-line operations of Gaia but for generations to come.
Today is the 100th anniversary of the birth of author Roald Dahl, who was born in Llandaff, Cardiff, on 13th September 1916. To celebrate this occasion, Cardiff University’s School of Chemistry has tried to recreate some of the phenomena described in one of Dahl’s children’s books, George’s Marvellous Medicine. Enjoy!
There’s been a lot of discussion in the news about changes to electoral constituencies in the United Kingdom proposed by the Boundary Commissions for England, Wales, Scotland and Northern Ireland. These proposals are intended to achieve two goals: (a) to reduce the total number of constituencies (and hence Members of Parliament) from 650 to 600; and (b) to ensure that the resulting constituencies contain roughly the same number of votes (within 5% either way of the mean number).
In a bit more detail: each constituency in the UK should contain roughly the same number of eligible voters, the so-called “electoral quota” which is reached by dividing the total electorate of the UK by the number of required constituencies, except for the Isle of Wight and two Scottish island constituencies. The quota is then 74,769, based on the electoral register as it stood on 1 December 2015.
The purported aim of (a) is to reduce the running cost of Parliament. I’d be more convinced of that if the previous Prime Minister hadn’t appointed no fewer than 260 Members to the House of Lords, at considerably greater expense than the saving incurred by losing 50 MPs from the House of Commons. The intention of (b) is more reasonable, but it does threaten the rationale of the constituency-based system as it creates some larger and less homogeneous constituencies.
The Boundary Commisssion for Wales has proposed that the Welsh MPs be reduced from 40 to 29, which means the loss of some historically important constituencies altogether and a significant rearrangement of many others. In fact there isn’t a seat in Wales that isn’t changed in some way. Here’s what the proposals mean for Cardiff, with the existing constituencies on the left and the proposed boundaries on the right:
I reside in Cardiff West (marked 12 on the left). You will see that the proposal involves extending this constituency on the western side of the River Taff down towards Cardiff Bay. This splits the former constituency Cardiff South and Penarth (11) into two, the western part (mainly Penarth) being absorbed into a new constituency called Vale of Glamorgan East (20 on the right). The other big change is that Cardiff Central (9 on the left) is eliminated entirely, absorbed by an enlarged Cardiff North (18 on the right, formerly 10 on the left) and a new Cardiff South and East (19) on the right. The net change is the loss of one seat in the City of Cardiff, which is currently held by Labour MP Jo Stevens.
I’m sure there’ll be quite a strong reaction to these changes, not least because they are based on the electoral register as it was on December 1st 2015 because the switch to individual electoral registration meant that 770,000 names dropped off the list before this date. The list also does not reflect those who registered to vote ahead of the EU referendum in June.
Going back to Wales for a moment, I think it’s unfair that while Scotland excluded two island constituencies from the quota formula to reflect their specific character, the same did not happen for Ynys Môn (Anglesey), a constituency which has been around since 1536, but which is now to be enlarged into a new entity called Ynys Môn and Arfon. I’m sure someone will comment on that!
Anyway, these are proposals and there is now a period of consultation. The final boundaries will not be determined until 2018.
I was listening to this wonderful track yesterday and couldn’t resist reposting a piece I wrote I wrote about it over 7 years ago. If I were ever to be asked on one of those programmes where you have to pick examples of your favourite music, this would probably be the first I’d write on my list.
Years ago in 1980, when the great pianist Bill Evans passed away suddenly, Humphrey Lyttelton paid tribute to him on his radio programme “The Best of Jazz” by playing a number of tracks featuring him. I didn’t really know much about Bill Evans at the time – I was only 17 then – but one track that Humph chose has been imprinted on my mind ever since, and it’s one of those pieces of music that I listen to over and over again.
The track is On Green Dolphin Street, as recorded in 1958 by the great Miles Davis sextet of the time that featured himself on trumpet, John Coltrane on tenor sax, Julian “Cannonball” Adderley on alto sax, Jimmy Cobb on drums, Paul Chambers on bass and Bill Evans on piano. This is the same band that played on the classic album Kind of Blue, one of the most popular and also most innovative jazz records of all time, which was recorded a bit after the recording of On Green Dolphin Street. I love Kind of Blue, of course, but I think this track is even better than the many great tracks on that album (All Blues, Flamenco Sketches, Blue in Green, etc). In fact, I’d venture the opinion – despite certainty of contradiction – that this is the greatest Jazz recording ever made.
On Green Dolphin Street was suggested to Miles Davis the band’s leader by the saxophonist Cannonball Adderley. It was the theme tune from a film from the late 1940s. It’s also the title of a more recent very fine novel by Sebastian Faulks.
I think the Miles Davis version demonstrates his genius not only as a musician himself but also as a bandleader. On Green Dolphin Street definitely bears the Miles Davis hallmark, but it also manages to accommodate the very different styles of the other musicians and allows them also to impose their personality on it. This is done by having each solo introduced with a passage with the rhythm section playing a different, less propulsive, 3/4 time behind it. This allows each musician to set out their stall before the superb rhythm section kicks into a more swinging straight-ahead beat (although it still keeps the 3/4 feel alongside the 4-4, courtesy of brilliant drumming by Jimmy Cobb) and they head off into their own territory. As the soloists hand over from one to the other there are moments of beautiful contrast and dramatic tension, especially – and this is the reason why Humph picked this one in 1980 – when Bill Evans takes over for his solo from Cannonball Adderley. He starts with hesitant single-note phrases before moving into a richly voiced two handed solo fully of lush harmonies. It’s amazing to me to hear how the mood changes completely and immediately when he starts playing, and it always sends shivers down my spine.
Not that the other soloists play badly either. After Bill Evans’s short but exquisite prelude, Miles Davis takes over on muted trumpet, more lyrical and less introspective than in Kind of Blue but still with a moody, melancholic edge. He’s followed by John Coltrane’s passionately virtuosic solo which floods out of him in an agonized stream which contrasts with Miles’ poised simplicity. By contrast, Cannonball Adderley is jaunty and upbeat, sauntering through his solo up to that wonderful moment where he hands over to the piano. Then Miles Davis takes over again to take them to the conclusion of the piece.
I’m not into League tables for music, but this is definitely fit to put up alongside the greatest of them all…
We outline a new method to compute the Bayes Factor for model selection which bypasses the Bayesian Evidence. Our method combines multiple models into a single, nested, Supermodel using one or more hyperparameters. Since the models are now nested the Bayes Factors between the models can be efficiently computed using the Savage-Dickey Density Ratio (SDDR). In this way model selection becomes a problem of parameter estimation. We consider two ways of constructing the supermodel in detail: one based on combined models, and a second based on combined likelihoods. We report on these two approaches for a Gaussian linear model for which the Bayesian evidence can be calculated analytically and a toy nonlinear problem. Unlike the combined model approach, where a standard Monte Carlo Markov Chain (MCMC) struggles, the combined-likelihood approach fares much better in providing a reliable estimate of the log-Bayes Factor. This scheme potentially opens the way to…
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Feel free to comment on any of the posts on this blog but comments may be moderated; anonymous comments and any considered by me to be vexatious and/or abusive and/or defamatory will not be accepted. I do not necessarily endorse, support, sanction, encourage, verify or agree with the opinions or statements of any information or other content in the comments on this site and do not in any way guarantee their accuracy or reliability.
In the Dark 