The Sun - II Alexei Gilchrist
Some resources • http://www.nineplanets.org/sol.html • “The Universe: Secrets of the Sun” video Secrets of the Sun – Search on youtube (references are to clips here http://www.youtube.com/view_play_list?p=4EEF5255D3EEF425 parts 1-5) • Chp 14 of Voyages (references and links at end) • References noted in these slides
Why does the sun shine? Long and fascinating history involving - geology - evolution - meteors - E = mc 2 - quantum mechanics - particle physics - two Nobel prizes More detail: http://nobelprize.org/nobel_prizes/physics/articles/fusion/index.html http://www.cerritos.edu/ladkins/a106/sunshine.htm http://nobelprize.org/nobel_prizes/physics/articles/bahcall/
How much energy does the sun put out? Imagine an ice cube in the sun during summer ... takes about 30min to melt say If you put all those ice cubes out there at same That ice cube could time – a shell 1cm thick and be anywhere in a surrounding the sun it sphere with radius would all melt in about 30 150,000,000 km min around the sun ... 1 calorie (=4.2 J) -> 1g water by 1 degree o C 6 W = 6.3 x10 2
How much do we produce? recommended daily dietary intake ~ 2000 Calories (food Calorie = 1000 calories) NB most of the energy we consume goes in heat
Age of the sun? First edition of The Origin of The Species by Natural Selection In 1859 Charles Darwin estimated it at 300 million years based on the erosion of the Weald in south England (time enough for evolution to occur) http://en.wikipedia.org/wiki/Image:KentGeologyWealdenDomeSimple.svg
Problem ... no fuel source known Chemical? No source known that would supply that much energy The sun would burn out in only 3,000 years
Problem ... no fuel source known Meteoric impact? Initially favored by Lord Kelvin That some form of the meteoric theory is certainly the true and complete explanation of solar heat can scarcely be doubted, when the following reasons are considered: (1) No other natural explanation, except by chemical action, can be conceived. (2) The chemical theory is quite insufficient, because the most energetic chemical action we know, taking place between substances amounting to the whole sun's mass, would only generate about 3,000 years’ heat. (3) There is no difficulty in accounting for 20,000,000 years’ heat by the meteoric theory. ... What then are we to think of such geological estimates as [Darwin's] 300,000,000 years for the “denudation of the Weald”? but a huge number should be hitting earth too ... http://nobelprize.org/nobel_prizes/physics/articles/fusion/index.html
Problem ... no fuel source known Gravitational Contraction? Helmoltz & Kelvin Sun shrinking ~ 7inches / day 7000 miles in 10,000 years (recorded history) not noticeable at that time Estimated age of the sun at 18 million years (Not enough for evolution) Darwin removes mention of timescales in later editions of The Origin of The Species by Natural Selection
http://fds.oup.com/www.oup.co.uk/images/oxed/children/yoes/atoms/fission.jpg Fission 1896 Radioactivity discovered (Henri Becquerel) Heavy unstable nuclei split apart release of energy The discovery of the radio-active elements, which in their disintegration liberate enormous amounts of energy, thus increases the possible limit of the duration of life on this planet, and allows the time claimed by the geologist and biologist for the process of evolution. Rutherford, 1904 Problem – requires massive unstable elements ... inconsistent with sun’s density and composition
Fusion Nucleus 2 protons 2 neutrons 1905 Albert Einstein: E = mc 2 Sun is mostly Hydrogen weight He < weight 2p +2n Fusion will form Helium (Aston 1920 looking for isotopes of Neon) Lots of energy released Difference in weight is released as energy ... a lot of energy
but like charges repel... protons will repel each other as they both have +ve charge Is the sun hot enough so that they slam into each and get close enough for fusion to occur? Eddington 1925: Sun not collapsing – hydrostatic equilibrium (pressure in = pressure out) for a gas (pressure) = (density) (temperature) working from surface down estimated core of sun at 10 million K Not hot enough!
Quantum again Since matter has wave-like behaviour we can get “quantum mechanical tunneling” Even though the protons don’t have enough energy to fuse they can sort of leak into each other and fuse some of the time http://hyperphysics.phy-astr.gsu.edu/Hbase/quantum/barr.html#c1
p-p cycle Hans Bethe received the 1967 Nobel Prize in Physics "for his contributions to the theory of nuclear reactions, especially his discoveries concerning the energy production in stars"
The p-p cycle
neutrinos
neutrinos probability of hitting something in earth Hard to detect is < 1/1,000,000,000,000 100,000,000,000 pass through your thumbnail every second could travel through 100 light years of iron without hitting anything Detection: e.g. super-Kamiokande: first: o 50,000 tons of ultra pure water o 100,000 gallons of cleaning o 11,000 tv-sized detectors fluid (perchloroethylene) o detect flashes of light from a o Occasional collision with neutrino collision chlorine -> Argon o Detect the Argon o expect only a few atoms / week
http://www.oobject.com/ghost-particle-detectors/super-kamiokande/2172/ super-Kamiokande
“solar neutrino problem” too few neutrinos detected (factor of three) Energy correct; T of sun verified independently; rate depends on T 2 5 ! x3 is particularly good Raymond Davis, Jr. & Masatoshi Koshiba, 2002 Nobel Prize in Phyics "for pioneering contributions to astrophysics, in particular for the detection of cosmic neutrinos" Required a modification of our basic understanding of particle physics o neutrinos have mass o can oscillate between other types (electron neutrino, muon neutrino, tau neutrino) o Only electron neutrino detected initially Sudbury Neutrino Observatory
Secrets of the Sun (nuclear fusion) (1) 1:14 (5min)
Solar Cycle http://www.lmsal.com/YPOP/Spotlight/Tour/tour07.html o Solar activity goes on an 11 year cycle o last maximum in 2001 http://www.lmsal.com/YPOP/Classroom/Lessons/Cycles/Images/butterfly.gif
http://www.lmsal.com/YPOP/Spotlight/Tour/images/cycle2.jpeg
http://www.nso.edu/gifs/minmax.gif
Secrets of the Sun (solar cycle) (4) 4:40 (2min)
Magnetic environment o Suns activity is driven by magnetism (originating in movement of charged gasses) o Can measure this through the Zeeman effect Strong magnetic fields split the quantum energy levels and this can be seen in the spectra Sunspots are regions of strong magnetic fields
Magnetic Environment o coronal loops align with magnetic field lines http://stargazers.gsfc.nasa.gov/students/magnetism.htm http://www.space.com/scienceastronomy/solarsystem/trace_update_000926.html
Magnetic Environment o Suns magnetic field is enormously complex – the differential rotation twists the field lines (~ million poles)
Sunspots ... Plages... bright clouds: o higher temp and density Prominences... o usually originate near sunspots (release of energy from twisted magnetic field lines) o relatively cool: 60,000 K o loops can remain stable for hours or days o eruptions faster 1,300 km/s & heights of a million km
Solar flares o Violent eruptions (some of the largest explosions in solar system) a billion Mt of TNT o usually 5-10 minutes (largest several hours) o near solar maximum: several smaller flares a day; a large flare every few weeks o 10 million K ; lots of UV and X-rays o can cause solar quakes A solar quake from a flare o can emit large amount of coronal material e.g equivalent to mount everest (coronal mass ejections or CMEs) - bubble of 10s of millions of tons gas blown into space - can reach earch in a few days - can change the orbits of satellites - distorts earths magnetic field - disrupts communication satellites
Secrets of the Sun ( magnetics; coronal loops; sun spots; solar flares; sun quakes; coronal mass ejections) (2) 2:50 – (3) 1:38 (11min)
Solar wind o Discovered by observing comets tails o stream of charged particles o coronal gases are so hot particles can escape suns gravity o 400km/s outward o sun losing 10 million tons / year o bright regions of corona – gases trapped by magnetic fields o dark regions – magnetic field extends outwards o solar wind predominantly from these “holes”
Effect on Earth - auroras o interaction of solar wind with earths magnetic field o complex! aurora_img_2005254_sm http://science.nasa.gov/spaceweather/aurora/gallery_12oct01.html http://science.nasa.gov/spaceweather/aurora/gallery_12oct01.html
Effect on Earth - auroras http://en.wikipedia.org/wiki/Aurora_(astronomy)
Effect on Earth - auroras http://en.wikipedia.org/wiki/Aurora_(astronomy)
Effect on Earth - climate o “little ice age” in europe during maunder minimum (Thames froze at least 11 times) Why? Solar luminance change too small More ozone produced Recent model: UV changes 10x – 100x bigger transfer of heat around earth Absorbs sunlight changes wind patterns Warms stratosphere
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