Feeds:
Posts

## The birth and death of stars

A few months ago this story caught my attention on the BBC news website. It is an image of part of the Large Magellanic Cloud (LMC), a satellite galaxy of our Milky Way galaxy, and shows both star birth and star death.

The circular looking “shell” of gas towards the left of the image is a supernova remnant, part of the gases which have been blown off by an exploding massive star. To the right of the image is an area called the Dragon Nebula, which is an area of current star formation.

The LMC is about 170,000 light years from our Milky Way, visible to the naked eye from the Southern Hemisphere. It is a small irregular galaxy which is actually in orbit about our much larger Milky Way, and is so named because the first European to note it was Ferdinand Magellan, who was also captain of the first expedition to circumnavigate the Earth. It is called the Large Magellanic Cloud because near to it (and also visible to the naked eye) is a smaller irregular galaxy, which is called the Small Magellanic Cloud (astronomers are nothing if not inventive in their naming 😉 ).

In 1987 a massive star exploded (a supernova) in the LMC, SN1987A, which was the first naked-eye supernova visible since Kepler’s supernova in 1604. However, it is not the SN1987A supernova which is shown in this image, the supernova here is older than that, something we can determine from the size of the remnant (the expanding shell of gases which the supernova blows off when it explodes).

It may seem to be quite a coincidence to capture a supernova remnant and a region of star formation in the same image, but in fact it is not so surprising. The shock waves caused by a supernova explosion are thought to often trigger the collapse of giant molecular clouds which lead to new star formation, so stellar death leads to stellar re-birth. Not only that, but the new generation of stars will contain heavier elements which have been created in the massive star and its supernova. Elements up to iron can be created in the massive star itself, but the many elements beyond iron in the periodic table are mostly created in the supernova explosion itself.

The wispy (mainly) red areas in the image are due to the gases fluorescing, just as I have described in previous blogs, for example here and here. The red colour is due to the dominant line-emission process, the h-alpha emission in hydrogen. You may also notice some dark areas (lanes) in the right hand part of the image where the star formation is going on. This is not the absence of stars, but is due to stars being hidden by dust, the same kind of dust I mentioned in my blog on BICEP2 last week. To see through the dust and to see the stars which are currently still forming, we need to look in the infrared and millimetre, where we can see through the dust and see the much cooler “proto-stars”, I will blog about this in the near future.

## Djokovic denies Federer in a classic

Nova Djokovic denied Roger Federer his 8th Wimbledon title in a 5-set match which will go down as a classic. Both players sustained tennis of the highest level to thrill the crowd for over three and a half hours. At 2-5 down in the 4th set, and facing match point, it looked like it was all over for Federer, but remarkably he won 5 games in a row to take the 4th set 7-5 and take it into a 5th and deciding set.

Djokovic has described his victory in yesterday’s Wimbledon final as the most special of his career.

Federer won the first set in a tie-break, but then was broken early in the 2nd set, which Djokovic went on to take 6-4. Djokovic also took the 3rd set, this time in a tie-breaker, and when he stood at 5-2 up in the 4th set it looked like it was all over for Federer. But, digging deep and coming up with some amazing shots, Federer levelled the match at two sets all, and it looked like the dream of his winning his 8th Wimbledon was back on.

Importantly, after losing 5 games in a row, Djokovic won the opening game of the final set, which eventually went to 4-4 before Djokovic broke Federer’s serve for the 2nd time in the set, and then served out the match to take the final set 6-4. For a match which lasted for over three and a half hours, it was remarkable how high the level of tennis was for nearly the entire match. Although I was hoping Federer would win, no-one can deny that Djokovic played superbly well and it was a match he won rather than Federer losing it.

A number of commentators have said that, at soon to be 33, there is no reason that Federer cannot carry on for several more years. He has stayed remarkably injury-free for nearly his entire career, testimony to how balanced a player he is. For a player who has achieved everything in tennis very few things can still motivate him, but it is no secret that winning 8 Wimbledons is one thing he still wishes to achieve, so I fully expect Federer to be back in 2015 trying to win that elusive 8th title.

## Can Federer make it 8 Wimbledon titles?

Not for the first time, today Roger Federer stands on the verge of creating tennis history. This afternoon he will take on Novak Djokovic in the men’s final at Wimbledon, and should he win he will have won “The Championships” (as Wimbledon calls itself) more times than any other man in history. Currently, he holds 7 Wimbledon titles, and so jointly holds the record with Pete Sampras. And, in some ways, with William Renshaw from the 1800s, although I am not sure Renshaw can really be counted for reasons I will now explain.

Until 1922, the defending Wimbledon champion did not have to go through any qualifying rounds, he (or she) would merely play in the final against whoever had gone through a knockout competition to challenge him (or her). So, of Renshaw’s 7 titles, which he won in 1881-1886 and 1889, he only had to go through the “challenge rounds” in 1881 and 1889, his other 5 titles involved winning merely one match, the final. So, with all respect to Renshaw, I don’t think it is fair to compare his 7 titles to the 7 won by Sampras and Federer.

Sampras won his 7 Wimbledon titles from 1993-1995 and 1997-2000. For the best part of a decade, Sampras dominated Wimbledon. The only Wimbledon he failed to win between 1993 and 2000 was in 1996, when Dutchman Richard Krajicek won, beating Sampras in the Quarter Finals on his way to the title. Sampras also broke the record for the most number of major titles won (all four majors), eventually winning 14 before he retired.

Pete Sampras winning his first of 7 Wimbledon titles in 1993

Pete Sampras winning the last of his 7 Wimbledon titles in 2000

Federer won the first of his 7 Wimbledon titles in 2003, by which time the era of “serve-volleyers” had come to and end. The 2001 title was won by Croatian Goran Ivanišvić who was a serve volleyer, but the 2002 title was won by Australian Leyton Hewitt, who rallied from the baseline. Federer won Wimbledon in 2003-2007, 2009 and 2012. He was also runner-up in 2008, when he lost to Spaniard Rafael Nadal.

Roger Federer winning the first of his 7 Wimbledon titles in 2003

Roger Federer winning his 7th Wimbledon title in 2012

Federer has won a total of 17 major titles, so currently holds that record, but Nadal has now equalled Sampras’ total of 14 titles. And, should be win today, Federer will also become the oldest Wimbledon men’s champion in the open era, as he will soon turn 33.

There is also an interesting auxiliary rivalry to today’s match, as Djokovic now has Boris Becker helping him, and Federer has recently started employing Stefan Edberg to help him. As Becker and Edberg met each other in 3 successive Wimbledon finals (1988-1990), I am sure there is still a healthy rivalry between them, even though they are also good friends.

I for one will be shouting for Federer. I have said this before in previous tennis blogs, but for me Federer is the most skilful player since John McEnroe in the 1980s. His range of shots is, I believe, greater than anyone since McEnroe, and I also feel that Edberg has brought a new confidence to Federer coming to the net, which has never been a natural part of his game but could give him that extra element to win his 8th Wimbledon title in the twilight of his career.

My main fear for Federer is that his progress through Wimbledon this year has just been too easy. He’s only dropped one service game so far in the tournament, and hasn’t yet been challenged in the way that Djokovic will surely challenge him. But, he also knows what winning Wimbledon is all about, and must realise that his chances of winning that elusive 8th Wimbledon title are getting slimmer and slimmer with each passing year.

Fingers crossed that he manages to do it today!

## White Rabbit – Jefferson Airplane (song)

Today I thought I would share this great song by Jefferson Airplane – “White Rabbit”. This is pretty much the only Jefferson Airplane song I know. It was released in June 1967, during the “summer of love”. The song was written by the band’s lead singer Grace Slick in the winter of 1965/66 just before she joined the band, and is obviously about drugs (“And you’ve just had some kind of mushroom”) and the mind-expanding nature of hallucinogenic drugs with which people were experimenting at the time.

The song also contains references to Alice and other characters and scenes from Lewis Caroll’s famous stories “Alice’s Adventures in Wonderland” and “Through the Looking-Glass”, written in 1865 and 1871 respectively. In interviews Slick has said that she vividly remembers being read these stories as a child, and how the bizarre imagery in them made an early impression on her.

One pill makes you larger
And one pill makes you small
And the ones that mother gives you
Don’t do anything at all
When she’s ten feet tall

And if you go chasing rabbits
And you know you’re going to fall
Tell ’em a hookah-smoking caterpillar
Has given you the call
Call Alice
When she was just small

When the men on the chessboard
Get up and tell you where to go
And you’ve just had some kind of mushroom
And your mind is moving low
I think she’ll know

When logic and proportion
And the White Knight is talking backwards
And the Red Queen’s off with her head
Remember what the dormouse said

Here is the video of this great song. Enjoy!

## Wonga should be prosecuted

I heard last week that the “pay-day” loan company Wonga sent fake lawyer letters to its customers to intimidate them into repaying their outstanding debts. The financial watchdog the “Financial Conduct Authority” has ordered Wonga to compensate their customers, but it is not clear whether anyone will face criminal prosecution.

The pay-day loan company “Wonga” have been found guilty of sending fake lawyer letters to their customers

Surely doing this is illegal, as it amounts to fraudulent representation. I’m no legal expert, but my understanding of fraud is to make false representations with the aim of perfunctory gain. Wonga were pretending the letters were coming from lawyer firms precisely to gain financially (re-coup their outstanding loans), and so I don’t see why the people responsible for this should not face criminal prosecution.

Pay-day loans are something which have sadly become quite common in the last half a dozen years. Anyone who has watched afternoon TV (which I have ended up doing when ill last year when I got back from India) will have seen their advertisements. Out of curiosity, I have gone to the Wonga website to see how much interest I would pay if I borrowed £400 (the maximum one can borrow as a first time customer) for 35 days (5 weeks). The interest is an unbelievable £147.43, which translates to an annual interest rate of something ridiculous of nearly 6000%!!!!!

To borrow £400 for 35 days (5 weeks) would involve paying £147.43 in interest!!

The quote from Wonga’s UK Managing Director Tessa Cook in my screen capture above is, to say the least, less than sufficient. Not only should Wonga not be proud of making up fake lawyer letters, but the people involved should face prosecution.

## Does polarised glass have to be tinted?

I was listening to BBC Radio 5’s “Dr. Karl” phone-in last Wednesday/Thursday night (25th/26th), which had Wendy Zukerman (@wendyzuk on Twitter), a science journalist, replacing the usual Dr. Karl as he is currently travelling in the USA. One of the many interesting questions asked by listeners was “Does polarised glass have to be tinted?”. The question made me think that it was high time I wrote a blog about what polarisation is, and why wearing polarised sunglasses cuts down on glare (what with the summer here and all….)

## Light is an electromagnetic wave

Light is an example of a more general phenomenon called electromagnetic radiation, which also includes radio waves, x-rays, microwaves and the infrared. We can think of light as a wave which travels from its source, and in a vacuum it travels at the speed of light (it travels slower in other media, but in air it travels nearly at the speed of light in a vacuum). The light wave actually consists of a fluctuating electric field and a fluctuating magnetic field at right angles to each other, as the figure below shows. The blue wave is the changing electric field, the red wave is the changing magnetic field.

An example of an electromagnetic wave. The blue wave is the electric field, the red wave is the magnetic field. They are at right angles to each other, and the variation of one produces the other. As illustrated on the right, in this example the wave is travelling to the right, but if we looked at it end-on it would be coming towards us (a circle with dot in the middle is the way physicists show that something is coming out of the paper/screen).

## What is polarisation?

Normally light is unpolarised, which basically means that the direction of the electric field vector ($\vec{E}$ as shown in the diagram above) can be in any direction and is always changing as light waves stream from the source. In the diagram below, the unpolarised light is shown with four different directions (vertically, horizontally, and at 45 degrees each side of the vertical), but in reality all directions occur for unpolarised light.

If we pass this unpolarised light through a polarising filter, only the light whose electric field is in the direction of the “slits” in the polarising filter will be allowed through. So the light emerging to the right of the polarising filter is polarised. This is nicely shown in the figure below.

A polarising filter will only allow the light whose Electric field vector is in the same direction as the lines in the filter to pass through

If we now put a second polarising filter in the path of the polarised light, and the orientation of the second filter is the same as the first filter, then the light will be unaffected by the second filter because the light is already polarised. This is shown in the middle diagram in the figure below.

If, however, we put a second polarising filter in the path of that polarised light, and the orientation of the second polarising filter is not the same orientation as that of the first filter, then no light will emerge through the second filter. This is shown in the bottom diagram in the figure below.

Normally light is unpolarised, which means the electric field vector is at random orientations. When it passes through a polarising filter, only the Electric field vector in the direction of the slits in the filter can pass through, all other orientations are blocked. If we put a second filter at a different orientation to the first filter, no light will get through the second filter.

## Why do polarised sunglasses reduce glare near water?

When light is reflected off of a surface, such as water in a lake, swimming pool or the sea, the reflected light is polarised. The reasons for this are more involved than I want to go into in this non-technical blogpost, but it has to do with the direction in which the electric field can jiggle the electrons in the surface of the water. It can jiggle the electrons in the plane of the surface, but not perpendicular to the surface. This leads to the reflected light being polarised, in the sense that the reflected wave only has a polarisation parallel to the surface of the water. This is illustrated in the figure below.

When unpolarised light reflects off of a surface, such as water, it becomes polarised. The only reflected part is the light whose electric field vector is parallel to the reflecting surface.

This is why polarised sunglasses cut down so much on the glare at an outdoor swimming pool, a lake or on the beach. Polarised sunglasses have the polarising filters arranged so that the only light allowed through the filter is with the polarisation in the vertical direction, that is in the same direction as your body if you are standing up. Even in itself, this will cut down on even the direct light entering your eyes, as it cuts out all the light with the electric field vector in other directions, only allowing the light whose electric field vector is in the vertical direction to pass through. So, polarising sunglasses darken the scene, even if you are nowhere near water or other horizontal reflecting surfaces.

But, even more usefully, if you are standing up and look out towards water and the light which is being reflected off of the water, the polarised sunglasses are going to cut out all the light which has been reflected off of the water’s surface! This is because that light is polarised parallel to the surface of the water, which is at right angles to the polarising filter in your sunglasses, so it does not get through. This significantly reduces the glare one would normally have if you looked at strong sunlight being reflected off of water.

## Does polarised glass have to be tinted?

Going back to the original question, “Does polarised glass have to be tinted?”, I guess the correct answer is that it depends what you mean by “tinted”. Polarised glass will always cut down on the amount of unpolarised light getting through, so anything illuminated by unpolarised light will look darker through polarised glass. But, tinting is a separate thing from polarisation. Cheap sunglasses are tinted, in that they have darkened glass or plastic to cut down on the amount of light passing through to your eye (and, hopefully, something to filter out the damaging UV rays from getting to your eyes). But, tinted glass does not polarise the light.

It is possible to also add tint to polarised glass so that even the “clear” parts of the filter, which allow light through, will cut down on the amount of that light. But, polarised glass and tinted glass are really two separate things. If you can afford it, polarised sunglasses are better, but they are also a lot more expensive than tinted sunglasses. Personally, I break (usually by sitting on) any sunglasses within a few months of buying them, so I have never bought an expensive pair of sunglasses, nor am I very likely to. But, if you are less clumsy than I am, polarised sunglasses are very nice and kind on the eyes.

So, a rather complicated answer to a simple question 🙂