Presentation on theme: "Walking on the Sun by Smash Mouth"— Presentation transcript:
1 Walking on the Sun by Smash Mouth Donna Kubik Spring, 2006
2 Walking on what? What is the surface of the sun? Although astronomers talk about the surface of the Sun, the Sun is so hot that it has no liquid nor solid materialIt is comprised totally of gas that gets denser and denser toward the centerThe Sun contains >99.85% of the total mass of the solar system
3 Walking on the photosphere? The Sun appears to have a surface only because most of its visible light comes from one specific layer, called the photosphere.The photosphere is the lowest of 3 layers comprising the Sun’s atmosphereBecause the upper 2 layers are transparent to most wavelengths of visible light, we see through them down to the photosphere.We cannot see through the photosphere, so everything below the photosphere is called the Sun’s interior
6 Limb darkening Sun appears darker near the edges This is called limb darkening
7 Limb darkeningAt the edges, we are looking through more of the cooler atmosphere, so there is more absorption of the photons from the hottest (innermost) part of the photosphereIn the center we can receive more photons from the hotter part of the photosphere4000 K5800 K
8 GranulationGranulation is the fine grain structure of the photosphere.Individual granules are about 1000 km across.The granulation is constantly changing, usually over time scales of minutes or less.
9 Granulation Darker because cooler Brighter because hotter Each granule is a convective cell which consists of a bright, roughly-polygonal area of hot rising gas, and a cooler edge of descending gasThe rising and descending is determined via Doppler shift of spectral linesDarker because coolerBrighter because hotterConvectionin photosphere
10 Granulation Darker because cooler Brighter because hotter The energy (E) and temperature (T) according to Stephan- Boltzman law: E~T4So more photons per area emitted from hot regionsDarker because coolerBrighter because hotterConvectionin photosphere
12 The EUV Sun The name, chromosphere “sphere of color” is misleading The name suggests it is the layer we normally seeBut the chromosphere’s light is swamped by that of the photosphere
13 The EUV SunThe chromosphere is only visible when the photosphere is blocked, as during a total solar eclipse, or when viewed at nonvisible wavelengths that the chromosphere is especially bright (as EUV), or when viewed through a filter (Ha) that blocks most of the photosphere’s light
14 The EUV SunImage taken at EUV wavelengths by SOHO (Solar and Heliospheric Observatory) operated by ESA and NASA.The UV light originates from the lower regions of the chromosphereThese wavelengths also indicate active regions.
15 SupergranulationThe dark graininess seen in the image is due to supergranulation.Supergranules contain ~ granulesTypical diameter of a supergranule is slightly larger than the earth’s diameterThe source of this light is the chromosphere
16 Spicules Spicules Supergranules High resolution images of the chromosphere, taken through an Ha filter, reveal numerous spikes, which are jets of gas called spiculesSpicules are usually located on the edge of supergranulesSpicules rise for several minutes at 45,000mph to a height of ~10,000km
17 SpiculesThe image shows spicules on the limb of the Sun as imaged by the Big Bear Solar Observatory.It shows a superposition of 11 limb images taken at different wavelengths
18 Sunspots inhibit formation of supergranules In these photos taken at the same time,there are no supergranules where there are sunspots.
19 Solar observatories Big Bear Solar Observatory The Big Bear Solar Observatory is located in the middle of Big Bear Lake (in CA) to reduce the image distortion which usually occurs when the Sun heats the ground and produces convection in the air just above the groundTurbulent motions in the air near the observatory are also reduced by the smooth flow of the wind across the lake instead of the turbulent flow that occurs over mountain peaks and forests.Big Bear Solar Observatory
20 Solar observatoriesIn addition to the atmospheric effects, solar telescopes suffer from heating by sunlight of the optics and the air within the telescope tube.This causes the image to shiver and become blurred.Modern solar telescopes are either vacuum telescopes, filled with helium or use careful control of the optic's temperature to reduce heating of the air in the telescope.Big Bear Solar Observatory telescopes
21 Solar observatoriesThe 65 cm and 25 cm telescopes are evacuated to avoid air turbulence inside the telescope tubes caused by the solar beam heating air molecules.Special white paint used inside and outside the observatory diffusely reflects sunlight and radiates heat away to reduce turbulence due to solar heating.Big Bear Solar Observatory telescopes
22 Solar observatoriesSome solar telescopes look very different from other optical telescopesKitt Peak National Observatory
23 Solar observatoriesClose to the ground the heating effect of the Sun causes a layer of hot, turbulent air, which makes images formed by mirrors near the ground unsteady, so the first mirror (heliostat) is often placed on a tall tower
24 Solar towers National Solar Observatory Sunspot, New Mexico Kitt Peak, Arizona
25 The Radio SunRadio image taken from Japan’s Nobeyama Radio ObservatoryThe most active regions are the most luminous.The radio image provides information about the transition region between the chromosphere and corona.
27 Corona viewed during eclipse The glow of the corona is a million times less bright than that of the photosphereLike the chromosphere, the corona can only be seen when the photosphere is blocked by special filters, at non-visible wavelengths at which the corona is especially bright, or when the disk of the Sun is blocked during a total solar eclipse…….
28 Coronagraph…..or by using a special instrument called a coronagraph that artificially blocks the disk of the Sun so that it can image the region surrounding the photosphere
29 CoronagraphA very common way to observe the corona is to cover the bright disk of the Sun.This creates a sort of mini-eclipse and allows us to see the Sun's fainter outer atmosphere
30 What can you see with a coronagraph? Streamers are structures formed by the Sun's magnetic field. They can last for months.Sometimes streamers go unstable and erupt in huge magnetic bubbles of plasma known as coronal mass ejections (or CMEs) that blow out from the Sun's corona and travel through space at high speed.
31 CoronaIt seems that the temperature should decrease as one rises through the Sun’s atmosphere (moving away from the apparent heat sourceIt does decrease from the photosphere (~5800K) to the chromosphere (~4000K), but then it rises to much higher temps in the corona (1-2 million K)!
32 CoronaUnexpected increase in temperature was discovered in about 1940 when Fe XIV (an iron atom stripped of 13 e-) was detected in the spectrum of the coronaTakes lots of energy to strip so many electrons from an atom, so the corona must be very hot
33 CoronaAstronomers have mounting evidence that the corona is heated by energy carried aloft and released there by the Sun’s complex magnetic fields (more on that later)
34 TRACETRACE (Transition Region and Coronal Explorer) is a NASA space telescope designed to provide high resolution images and observation of the photosphere and transition region to the corona.The satellite, launched in April 1998
35 TRACEThe telescope is designed to take images in a range of wavelengths from visible light, through the Lyman alpha line to far ultraviolet.The different wavelength passbands correspond to plasma emission temperatures from 4,000 to 4,000,000 K.Sun-synchronous (98°) orbit of 600×650 km.
36 Sun-synchronous orbit Sun-synchronous (98°) orbit of 600×650 km.This type of orbit is designed to keep the satellite in full sun light for nine months a year.The orbit moves the satellite to the west at the exact same rate that the sun appears to move across the Earth's surface.
37 CoronaIf the temperature is to high, why doesn’t the corona outshine the photosphere?According to according to Stephan-Boltzman law: E~T4So more photons should be emitted per area emitted from hot regions!?But the density of the corona is very, very, very low, otherwise it would outshine the photosphere!
38 Solar windThe Sun’s gravity keeps most of its atmosphere from escaping to space, but some of the gas in the corona is moving fast enough to escape.This is the solar wind
39 Space weather Solar Wind speed: 330.9 km/s density: 2.5 protons/cm3 The solar wind is one aspect of space weatherYou can view the current space weather conditions and the space weather forecast atSPACE WEATHER Current ConditionsSolar Wind speed: km/s density: 2.5 protons/cm3
40 Solar wind Solar Wind speed: 330.9 km/s density: 2.5 protons/cm3 The solar wind is comprised mostly of hydrogen and helium nucleiHydrogen nuclei are protonsSPACE WEATHER Current ConditionsSolar Wind speed: km/s density: 2.5 protons/cm3
41 Solar wind Solar Wind speed: 330.9 km/s density: 2.5 protons/cm3 The solar wind particles reach speeds up to 805 km/sThe wind achieves these high speeds in part by being accelerated by the Sun’s magnetic fieldSPACE WEATHER Current ConditionsSolar Wind speed: km/s density: 2.5 protons/cm3
42 Solar wind Solar Wind speed: 330.9 km/s density: 2.5 protons/cm3 The Sun ejects a million tons of matter each secondEven at this rate of emission, the mass loss due to the solar wind will amount to only a few tenths of a percent of the Sun’s total mass throughout its lifetimeSPACE WEATHER Current ConditionsSolar Wind speed: km/s density: 2.5 protons/cm3
43 SOHO orbit is sunward of Earth SOHO (Solar and Heliospheric Observatory), operated by NASA and ESA, is designed to study the internal structure of the Sun, its extensive outer atmosphere and the origin of the solar wind, the stream of highly ionized gas that blows continuously outward through the Solar System.SOHO orbit is sunward of EarthNot to scale
44 SOHO orbit is sunward of Earth All previous solar observatories have orbited the Earth, from where their observations were periodically interrupted as our planet `eclipsed' the Sun.A continuous view of the Sun is achieved by operating SOHO from a permanent vantage point 1.5 million kilometers sunward of the EarthSOHO orbit is sunward of EarthNot to scale
45 Lagrange pointsThe Italian-French mathematician Joseph-Louis Lagrange discovered five special points in the vicinity of two orbiting masses where a third, smaller mass can orbit at a fixed distance from the larger masses.
46 Lagrange pointsOf the five Lagrange points, three are unstable and two are stable.The unstable Lagrange points - labeled L1, L2 and L3 - lie along the line connecting the two large masses.The stable Lagrange points - labeled L4 and L5 - form the apex of two equilateral triangles that have the large masses at their vertices.SOHO
47 Lagrange pointsThe L1 point of the Earth-Sun system provide an uninterrupted view of the sun and is the location of SOHOSOHO
48 Lagrange pointsThe L2 point of the Earth-Sun system is the location of WMAP and (perhaps by the year 2011) the James Webb Space Telescope.The L1 and L2 points are unstable on a time scale of approximately 23 days, which requires satellites parked at these positions to undergo regular course and attitude corrections.
49 The quiet Sun vs. the active Sun Granules, supergranules, spicules, and the solar wind occur continuously. They are features of the quiet Sun.Active SunBut the Sun’s atmosphere is periodically disrupted by magnetic fields that stir things up, creating the active Sun.
50 Solar magnetic fieldIn contrast to the Earth, the Sun has a very weak overall magnetic field (average dipole field).However, the solar surface has very strong and tremendously complicated magnetic fields.Because the surface magnetic fields are so complex, solar astronomers use computers to simulate the Sun's magnetic fields.
51 Solar magnetic fieldIt is the dynamics of the Sun’s magnetic fields that is thought to cause many of the features of the active Sun
52 Discovery of sunspotsSunspots are one of the features of the active SunGalileo looked at the Sun through his telescopeOne should NEVER look directly through a telescope at the SunThis caused Galileo to suffer from partial blindness.
53 Discovery of sunspots Galileo did see spots on the Sun These were sunspotsThis animation shows a sequence of drawings made by Galileo as he observed the Sun from June 2nd to 26th, 1612.
54 Sunspots are cooler spots UmbraPrenumbraA typical sunspot is 10,000 km across and lasts between a few hours and a few mothsIt is comprised of two partsThe dark, central region is called the umbraThe brighter ring around it is called the prenumbra
55 Sunspots are cooler spots UmbraPrenumbraSeen without the surrounding very bright granules that outshine it, the umbra appears red and the penumbra orangeFrom Wein’s Law lmax=0.0029/TThe orange umbra is ~4300 KThe red penumbra is ~5000 KBoth are cooler than the surrounding 5800 K photosphere
56 Zeeman effectIn 1908, George Ellery Hale discovered that sunspots are directly linked to magnetic fieldsWhen he observed the spectra from sunlight coming from a sunspot, he found that each spectral line in the normal solar spectrum was flanked by additional, closely-spaced spectal lines not usually observed
57 Zeeman effectThis “splitting” of a single spectral line into two or more lines is called the Zeeman effectPieter Zeeman first observed such splitting in the laboratory in 1896
58 Zeeman effectZeeman showed that an intense magnetic field splits the lines of a light source if the source is inside the fieldThe more intense the magnetic field, the more the split lines are separated
59 SunspotsThe intense magnetic field below a sunspot strangles the normal up-flow of energy from the hot solar interior, leaving the spot cooler and therefore darker than its surroundings
60 SunspotsThe suppression of the bubbling convective motions forms a kind of plug that prevents some of the energy in the interior from reaching the surface.As a result, the material above the plug cools and becomes denser, causing it to plunge downward at up to 3,000 miles per hour, according to new observations from SOHO
61 SunspotsThis time-lapse movie shows in five seconds what happens in 20 minutes on the Sun's surface near a sunspot.This sunspot measured about 25,000 kilometers across.Visible is boiling granulation outside the sunspot, inward motion of bright grains in the outer penumbral region toward the sunspot, and the churning of small magnetic elements between solar granules.
62 SunspotsSunspots themselves are relatively cool regions of the solar surface depressed by magnetic fields.The dark lanes surrounding the sunspot are called penumbral filaments, and recent computer simulations have shown that their behavior is also dominated by magnetic fields.The movie was taken with the Dutch Open Telescope
63 SunspotsSunspots revealThe solar cycleThe Sun’s rotation
64 Differential rotation Sun rotates differentially25 days for one rotation at equator27 days at latitude 30 deg33 days at latitude 75 deg35 days near poles
65 The Solar Cycle Sunspot maximum and minimum occur on 11-year cycle Orientation of the Sun’s magnetic field flips every 11 yearsSolar cycle is ~22 years
66 Butterfly diagramSunspots do not appear at random locations over the surface of the sun but are concentrated in two latitude bands on either side of the equator.
67 Butterfly diagramA butterfly diagram showing the positions of the spots for each rotation of the sun since May 1874 shows that these bands first form at mid- latitudes, widen, and then move toward the equator as each cycle progresses
68 The Solar CycleProminences, flares, and plages vary with the same 11-year cycle as sunspotsCoronal mass ejections, the major source of hazardous particles from the Sun, occur with varying frequency, but never totally cease.
69 Filaments, plages, and prominences Hotter, therefore brighter, regions in chromosphereCreated by magnetic fields under the photosphere just before they they emergeProminences are filaments viewed from the sideAll associated with sunspotsProminencesPlagesFilaments
70 Filaments, plages, and prominences This image of 1,000,000K gas in the Sun's thin, outer atmosphere indicates ionized iron at 171 ÅThe loops of energized particles clearly follow magnetic field lines around an active region.
71 Filaments, plages, and prominences This image of 1-million degrees Kelvin gas in the Sun's thin, outer atmosphere which detects ionized iron here at 171 ÅThe loops of energized particles clearly follow magnetic field lines around an active region.Compare loops and prominences (left) to models of Solar magnetic fields (right)
72 The x-ray SunThis x-ray image was obtained by the Japanese observatory Yohkoh (Sunbeam), a collaborative effort with the US and UK.The x-rays originate from the Sun’s corona.
73 YohkohThe Japanese satellite, known as Yohkoh ("Sunbeam"), a cooperative mission of Japan, the USA, and the UK, was launched in 1991 (ended operation in 2005)The scientific objective has been to observe the energetic phenomena taking place on the Sun, specifically solar flares in x-ray and gamma-ray emissions
74 The x-ray SunThe brightest regions correspond to violent solar flares which send high energy particles to Earth.Darker regions denote cooler areas which are called coronal holes, because gases can escape this region.
75 Solar flares in the chromosphere Violent eruptive events, solar flares, send out vast quantities of high-energy particles as well as x-rays and UV radiation.Lots of flares at sunspot maximumCan last for hours
76 Solar flares vs. prominences Solar flares are more sudden and violent events than prominences.While they are thought to also be the result of magnetic kinks, flares do not show the arcing or looping pattern characteristic of prominencesFlaresProminences (which are filaments viewed from the side)
77 Solar flares vs. prominences Flares are explosions of incredible power, rising local temperatures to 100,000,000 KProminences release their energy over days or week, while flares release their energy in minutes or hoursFlaresProminences (which are filaments viewed from the side)
78 Coronal mass ejections In the foreground of the 15 degree wide field of view, a bubble of hot plasma, called a coronal mass ejectionCan alter the Sun’s magnetic fieldOften associated with solar flaresImage from SOHO using coronagraph
79 Coronal mass ejections Another Image of a CME from SOHO using coronagraph
80 Effect on EarthSome coronal mass ejections, solar flares, and prominences head toward EarthTakes 8 minutes for radiation to arriveTakes a few days for particles to arriveCan produce auroraCan disrupt communications
81 Maunder Minimum There are irregularities in the cycles Sometimes one pole reverses before the otherSometimes no sunspots for decades (as from , Maunder Minimum)
82 Solar cycle predictions From SCIENCE VOL MARCH 2006Researchers at the National Center for Atmospheric Research (NCAR) predict that the next peak in sunspots will come a little late but will be far bigger than the last peak—bigger, in fact, than all but one of the 12 solar maxima since 1880.
83 Solar cycle predictions They found that it takes a good 20 years for the magnetic remnants of past sunspots to recirculate deep into the interior, where the twisting action of the sun’s rotation amplifies them, and to rise back to the surface near the equator as the next cycle’s sunspots.
84 Solar cycle predictions The model did an impressively accurate job “hindcasting” the size and timing of past cycles.That track record made researchers confident that the next solar cycle will be 30% to 50% stronger than the last solar cycle.The next cycle will begin 6 to 12 month later than average
85 Where does the Sun’s energy come from? We see hot gas, intense magnetic fields, and the many features of both the quiet and active sunWhere does the energy come from?Can’t come from the hot gas or magnetic fields; they have no mechanism to create energy
86 Where does the Sun’s energy come from? In 1905, Einstein showed that mass can be converted into energy: E=mc2In 1920’s, Eddington proposed that temperatures in the core of the sun are high enough to fuse H to He.In this reaction, a tiny amount of mass is lost.This mass is transformed into a very large amount of energy – the energy of the Sun
87 4H He + neutrinos + gamma rays Thermonuclear fusionMass of 4 H atoms = x kg- Mass of 1 He atom = x kgMass lost = x kgE = mc2E = (0.048 x kg)(3x 108 m/s)2E = 4.3 x Joules4H He + neutrinos + gamma rays
88 Sources of the Sun’s energy The energy generated by hydrogen fusion is the Sun’s core eventually escapers through the photosphere into spaceThat energy makes the sun shine
89 Where does the Sun’s energy come from? There are 2 ways stars convert H to HeProton-proton chainCNO cycleBoth yield the same results4H He + energy
90 Where does the Sun’s energy come from? For stars with masses not greater than the Sun’s, the core temperature does not exceed 16 million K, so the proton-proton chain dominatesFor stars more massive than the sun, the core temperature is greater than 16 million K, and hydrogen burning occurs mainly via the CNO cycle
91 Sources of the Sun’s energy ~98.5% of the Sun’s energy comes from the p-p chain~1.5% of the energy comes from the CNO cycle
92 Proton-proton chain Hydrogen fusion - converts hydrogen to helium Possible because of high temperature and pressure in the Sun’s coreMass of 4 H > Mass of 1 HeResults in 4H He + neutrinos + gamma raysThe gamma rays balance inward force of gravity
93 Proton-proton chain There are 4 branches of the proton-proton chain The one below produces 85% of the Sun’s energyIn the other 3 branches, the 3He nucleus follows a different fateNeutrinos are produced by all branchesPhysicists want to study these neutrinos
94 CNO cycleThe initial reaction involves a carbon nucleus (with 6 protons) and a hydrogen nucleus (1 proton)Because of the large electrical charge of the carbon nucleus, there is a stronger electrical repulsionTherefore a higher temperature is needed in order for the reaction to take place
95 CNO cycleSince the CNO cycle recovers the original C nucleus, the carbon, nitrogen, and oxygen are unaffected, in net, by the reactionsSo it could start anywhere in the cycle with the addition of one proton to any of the carbon or nitrogen nuclei
96 CNO cycleConsequently, this cycle is often called the CN cycle (as They Might Be Giants call it!)
97 Why Does the Sun Shine? p-p chain! CN cycle! THEY MIGHT BE GIANTS The sun is large If the sun were hollow, a million Earths could fit inside. And yet, the sun is only a middle- sized star.The sun is far away About 93 million miles away, and that's why it looks so small And even when it's out of sight The sun shines night and day The sun gives heat The sun gives light The sunlight that we see The sunlight comes from our own sun's Atomic energy Scientists have found that the sun is a huge atom-smashing machine. The heat and light of the sun come from the nuclear reactions of hydrogen, carbon, nitrogen, and helium The sun is a mass of incandescent gas A gigantic nuclear furnace Where hydrogen is built into helium At a temperature of millions of degreesWhy Does the Sun Shine?THEY MIGHT BE GIANTSThe sun is a mass of incandescent gas A gigantic nuclear furnace Where hydrogen is built into helium At a temperature of millions of degrees Yo ho, it's hot, the sun is not A place where we could live But here on Earth there'd be no life Without the light it gives We need its light We need its heat We need its energy Without the sun, without a doubt There'd be no you and me The sun is a mass of incandescent gas A gigantic nuclear furnace Where hydrogen is built into helium At a temperature of millions of degrees The sun is hot It is so hot that everything on it is a gas: iron, copper, aluminum, and many others.p-p chain!CN cycle!
98 Direct observation of nuclear processes in the Sun Since the sequence of events, the variety of reactions, and the number of assumptions are so numerous, direct verification of the postulated nuclear reaction is desirableThe most promising observations would involve measuring the neutrinos emitted in the nuclear reactionsNeutrinos can easily escape the SunIf astronomers could detect these neutrinos, they would have a means of probing the reactions occurring at Sun’s core.
99 Direct observation of nuclear processes in the Sun Early attempt by Ray Davis and colleaguesLooked for neutrinos via37Cl + n Ar +e-37Ar is radioactive and decays emitting an x-ray which can be recorded
100 Missing neutrinosThe 37Cl neutrino detector is a tank containing 100,000 gallons of perchloroethylene in the cavity 4,850 feet below ground in the Homestake Mine in Lead, S.D
101 Missing neutrinosBut only 1/3 of the expected number of neutrinos from the Sun were detectedMaybe there are 3 kinds of neutrinos that can change into one anotherIf so, then Ray Davis’ detector would only have detected 1/3 of the expected number of neutrinos emitted by the Sun
102 Neutrino oscillations Changing from on type of neutrino to another is called neutrino oscillationIf neutrinos oscillate, it implies neutrinos have mass
103 Super-KamiokandeNeutrinos can interact in water and give rise to Cherenkov lightThe Cherenkov light provides information about the neutrino energy, direction, and typeThis light can be detected by phototubes lining the inside of the Super-Kamiokande detector which is filled with waterIn 1998, Super-K determined that neutrinos produced in the atmosphere by cosmic rays do oscillateSuper-K
104 Neutrino detectorsIn 2001, evidence of oscillation of solar neutrinos was found in the combined data from Super-K and the Sudbury Neutrino Observatory (SNO)Since then, these oscillations have been confirmed using man-made neutrino beamsSNO
105 Missing neutrinos get 2002 Nobel Prize "for pioneering contributions to astrophysics, in particular for the detection of cosmic neutrinos""for pioneering contributions to astrophysics, which have led to the discovery of cosmic X-ray sources"Raymond Davis Jr.Masatoshi KoshibaRiccardo Giacconi 1/4 of the prize /2 of the prizeUSAJapanUniversity of Pennsylvania Philadelphia, PA, USAUniversity of Tokyo Tokyo, JapanAssociated Universities Inc. Washington, DC, USAb. 1914b. 1926b (in Genoa, Italy)
106 Missing neutrinos get 2002 Nobel Prize Raymond Davis Jr constructed a completely new detector, a gigantic tank filled with 600 tons of perchloroethylene, which was placed in a mine. When a neutrino hits a Cl atom, it can convert one of its neutrons into a proton, creating a radioactive atom of Ar. By measuring the amount of Ar produced, one can infer how many neutrinos were detected.Over a period of 30 years he succeeded in capturing a total of 2,000 neutrinos from the Sun and was thus able to prove that fusion provided the energy from the Sun. With another gigantic detector, called Kamiokande, a group of researchers led by Masatoshi Koshiba was able to confirm Davis’s results.
107 Solar modelHow does the energy produced in the core of the Sun get to us?By combining theoretical modeling of the Sun’s interior with observations of the energy that the sun produces, astronomers have created the standard solar modelThis is a mathematically-based picture of the structure of the Sun.The model seeks to explain both the observable properties of the Sun and the properties of the unobservable interior
108 Solar model There are 3 methods of energy transport Conduction ConvectionRadiation
109 Solar modelExperience tells us that energy always flows from hot regions to cooler onesThe efficiency of this method, called conduction, varies significantly from one substance to anotherConduction is not an efficient means of energy transport inside stars like the SunIt is important in compact stars like white dwarfs (later lecture)
110 Solar ModelIn the Sun, energy moves from the center to the surface by convection and radiative diffusionConvection zoneRadiation zone
111 Solar ModelCoreAt the very high temperatures of the core, all matter is completely ionized (stripped of its electrons).Photons move slowly out of the core into the next layer of the sun’s interior, the radiation zone
112 Solar Model Radiative zone Here the temperature is a bit lower, and the photons emitted from the core of the Sun interact continuously with the charged particles located there, being absorbed and re-emittedThis is called radiative transportThis occurs 80% of the way out to photosphere in the radiative zone
113 Solar Model Convection zone While the photons remain in the radiative zone, heating it and losing energy, some of the energy escapes into the convection zone.
114 Solar Model Convection zone Here hot gases rise to the photosphere and cooling gasses sink back into the convection zoneConvection cells become smaller and smaller, eventually becoming visible as granules at the solar surface (photosphere).
115 Solar modelAt the Sun’s surface, a variety of processes give rise to the electromagnetic radiation that we detect from Earth. Atoms and molecules in the photosphere absorb some of the photons at particular wavelengths giving rise to the Sun’s absorption-line spectrumGiven the temperature of the Sun, most of the radiation is emitted in the visible part of the spectrum, in agreement with the blackbody curve for a body at that temperature
116 Helioseismology The sun vibrates; discovered in 1960 Can study these vibrations to learn about the interior.Learned that the convective zone is twice as thick as first thoughtBelow the convective zone, the Sun rotates as a rigid body (not differentially)
117 HelioseismologyWith a technique that uses ripples on the Sun's visible surface to probe its interior, SOHO scientists have, for the first time, imaged solar storm regions on the far side of the Sun, the side facing away from the Earth.The new technique, which uses the Michelson Doppler Imager (MDI) instrument on SOHO, gives a warning of storms by creating a window to the far side of the Sun.
118 The Sun's motion around the Galaxy’s center Using the VLBA, astronomers plotted the motion of the Milky Way and found that the Sun is orbiting the Galaxy at about 135 miles per second.Used the motion of Sagittarius A* relative to distant quasars135 miles/secSgr A*
119 The Sun's motion around the Galaxy’s center The spiral arms extend in a direction opposite to our motionAt the moment, the motion of the Sun is toward the constellation of Hercules135 miles/secSgr A*
120 The Sun's motion around the Galaxy’s center It takes the Sun 226 million years to orbit the GalaxyThe last time the Sun was at this spot of its Galactic orbit, dinosaurs ruled the worldThe period of time is called a cosmic yearThe Sun has orbited the Galaxy about 20 times during its 5 billion year lifetime135 miles/secSgr A*