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The Science of the Sune know very little about the Sun although it provides our heat and light and drives mostW mechanisms on Earth from the weather to our food chain, and most of what we know is onlytheory. The theories we have used are modelledon similar things on Earth where they can be, sothey could be wrong, and for other processes wehave nothing to model them on.One thing we are certain of is the composition ofthe Sun: through absorption spectra we can tellthat its surface is made up of 71.0% (by mass)hydrogen, 27.1% helium and 0.97% oxygen, aswell as about eight other detectable elements. TheSun has seven different layers, like the geographicalmodel of the Earth: inner core, outer core,mantle and crust, but different.The core of the Sun has a density ten times that of lead – which rationally would mean that it is solid,but because it has a temperature of 15 million degrees Kelvin (K) (add 273 for degrees Celsius) thecore of the Sun is a gas. Because of this intense heat and the high density, fusion reactions take placereadily (two heavy hydrogen atoms making a helium atom), producing gamma rays (the most energeticform of radiation) and neutrinos which are notoriously difficult to detect; because of absorbanceand re-emittance, the one high-energy gamma ray leaves the Sun as 1000 low-energy photons (smallpackets of light).The next layer is the solar envelope, made up of the radiative and convective envelopes whichtogether make up 60% of the mass and 90% of the volume of the Sun. Its temperature is 4 million K.The cooler a gas is the less efficient it is at transferring energy via radiation, so it starts forming convectioncells. Hence the convective envelope, which is made up of layers of convection cells withthe smallest ones (but still about the size of the Earth) nearest the surface, and the separation in thesolar envelope.The light that we see from the Sun is from the photosphere; this is a comparatively thin layer, only acouple of hundred kilometres thick, of a much lower temperature (6000 K). At this point it has takena single photon of light 30,000 years to come from the core to the surface because of interactions onthe way (it cannot move 1 cm before hitting an atom and changing direction, even though at thespeed of light (c) it would take it 2.3 seconds to complete the journey).Even though the photosphere is technically the surface of the Sun, there are two more layers: thechromosphere and the corona. The chromosphere is red due to an abundance of hydrogen and is at7000 K (first mystery; nobody yet knows why, there are theories but none have been proved) whichis hotter than the photosphere, but even more surprising the corona has an average temperature of1 million K but can reach 3 million K in places. The corona is visible only during eclipses and is alow-density cloud of plasma (simply, a plasma is a gas where all electrons have been ripped offatoms so it is fully ionised); it is white but not as bright and many times larger than rest of the Sun.The Sun has a magnetic field much like the Earth’s magnetic field but about 100 times stronger; thisis distorted by the rotation of the Sun, which interestingly is 34.4 days at the top and bottom but 25.1days in the middle because the Sun is not a sphere but elliptical and a gaseous body. This distortionof the magnetic field causes sunspots and solar flares which I will explain later. The magnetic fieldflips like the Earth’s: the Sun’s magnetic field flips every 11 years (the Earth’s switch interval ismillions of years) and is followed directly by changes in sunspot activity, so I am going to have toexplain what they are.30
Sunspots are areas where the magnetic field of the Sun gets twisted and anarea of high flux density occurs (effectively a concentrated localised magneticfield) that protrudes though the Sun’s surface; this causes the area tocool, which is why it looks black because the area surrounding it is muchhotter. These magnetic protrusions cause solar flares – surges of magneticenergy released suddenly when a twist of magnetic field crosses itself. Asanyone who has been taught about magnets knows, field lines don’t cross;however, they don’t break either and magnetic reconnection occurs to amore energetically favourable situation, causing radiation that crosses theentirety of the electromagnetic spectrum so we can see it. The energyreleased by this is about equivalent to millions of 100-megaton (100 million ton) hydrogen bombs.That’s really big: 1,000,000,000,000,000,000 calories big! To put it in perspective a Mars Bar has230 calories in it. As these flares are one of the few things that can extend into the corona and areabout 20 million K, they could be what keeps the corona as hot as it is.Another possibility for this is coronal mass ejections (CMEs).A CME is a huge burst of plasma that releases a huge amount of material.In my research for this article I could find no references giving a reasonwhy CMEs happen, apart from the fact they coincide with a large solarflare some of the time. The shape of the CME follows that of the magneticfield. Unlike solar flares, which can be pre-empted although notquite predicted, CMEs cannot be predicted as yet. They can only be seenby placing a disc over the Sun (as shown left) because the Sun is sobright, which also explains why they were not seen until the Space Agestarted. A few years ago a very infrequent event occurred: a CME came directly at us, there werestunning Northern Lights but telecommunications were severely disrupted, the Earth’s atmospherewas in danger of being blown away and a large number of satellites had to be shut down when wesaw it coming because their circuits would have been fried by the high-energy particles. Happily thishappens only very rarely and our magnetic field protects us. There is, however, a constant lowerenergystream of particles which fall down gaps in the Earth’s magnetic field and heat up in theatmosphere causing the aurora; this stream of particles is called the solar wind and without it ourmagnetic field would have prevented any life forming on this planet.We have very few satellites watching the Sun; the main one is the Solar and Heliospheric Observatory(SOHO) which is now in its 11th year. This is placed at the first of five points around our planetwhere a satellite can orbit about a point of empty space due to cancellation of forces and gravitationalpotential, these are called Lagrange points.————————————————————————————————————————Thank you to Dr Lucie Green at Mullard Space Science Laboratory, University College London, forinspiring me to write this article.Appendices and further reading: www-solar.mcs.st-and.ac.uk/~lorna/WORK/moves, wwwastronomy.mps.ohio-state.edu/~dhw/Intro/lec7,www.astro.umd.edu/~miller/Gallery/sun/cme.gif,science.nasa.gov/headlines/y2000/ast13sep_1, science.msfc.nasa.gov/ssl/pad/solar/cmes, hyperphysics.phy-astr.gsu.edu/hbase/solar/sunspot,www.cnn.com/TECH/space/9903/09/coronal.ejections,www.nasa.gov/vision/universe/solarsystem/flare_sept7, www-solar.mcs.st-and.ac.uk/~lorna/WORK/moves, spaceweather.com/images2001/24sep01/cme_c3_big.gif, www.physics.montana.edu/faculty/cornish/lagrange, fusedweb.pppl.gov/CPEP/Chart_Pages/5.Plasmas/SunLayers, hesperia.gsfc.nasa.gov/sftheory/flare,hyperphysics.phy-astr.gsu.edu/hbase/solar/sun, science.msfc.nasa.gov/ssl/pad/solar/the_keyAlistair Barrie 6-231
Page 2 and 3: Contents:An Interview with Harry Pe
Page 4 and 5: The Bedales Science Magazine
Page 6 and 7: An Interview with Harry PearsonCan
Page 8 and 9: 6-2 Physics Trip to CERN, Genevaver
Page 10 and 11: The Final Century?t the end of Worl
Page 12 and 13: Spring at the North Polehere’s a
Page 14 and 15: PC hazards and the lawHAZARDOUS WAS
Page 16 and 17: Incinerators are some of the larges
Page 18 and 19: IJoseph Rotblatfind myself writing
Page 20 and 21: Many resins are brittle and unstabl
Page 22 and 23: RECYCLINGThe reprocessing of plasti
Page 24 and 25: and processed to drinking water sta
Page 26 and 27: Interview with Professor Tony Marmo
Page 28 and 29: Finally, what should Bedales be doi
Page 30 and 31: Hydrogen Fuel Cell Car(We built one
Page 32 and 33: • Less land needed for landfill s
Page 36 and 37: The 6-1 Physics Trip to Thorpe Park
Page 38 and 39: Stem Cell Researchlthough medicine
Page 40 and 41: The potential for technological adv
Page 42 and 43: How Aspirin Worksrostaglandins are
Page 44 and 45: effectively a single species model
Page 46 and 47: References and notes:[1] Roy Porter
Page 48: The B-Sci CrosswordAcross1. The pro

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