Gaitskell PH0021 Astronomy Lecture 19 (The Sun) v7 The Sun, in all its glory! Prof Rick Gaitskell Department of Physics Brown University See course pages for source

PH0008 Gaitskell Class Spring2002 Rick Gaitskell Sun Data

PH0008 Gaitskell Class Spring2002 Rick Gaitskell The Sun - Photosphere Size o Scale o Composition Compare terrestrial planets Compare Jovian planets Sun — GAS/PLASMA - No solids, even at core, despite pressure… Why does it appear as a well defined “ball”? o (i) Gas distribution is nearly spherical o (ii) Only seeing gas from thin layer of gas PHOTOSPHERE o Thin layer of gas 400 km o 1/2000 th radius (Rsun~0.7x10 6 km) o “Limb darkening”

PH0008 Gaitskell Class Spring2002 Rick Gaitskell Absorption Lines - Photosphere

PH0008 Gaitskell Class Spring2002 Rick Gaitskell The Sun - Structure of Photosphere Typical grain ~1000 km (hires solar images) [DEMO Silicon Oil & Al flakes]

PH0008 Gaitskell Class Spring2002 Rick Gaitskell Chromosphere Above Photosphere (  Photo ~0.01% of  Earth atmosphere) Is even less dense Chromosphere (  Chromo ~0.01% of  Photo ) o Difficult to see, except during real or artificial eclipse o Pink in colour! Why pink?? Emission Spectrum [BOARD]

PH0008 Gaitskell Class Spring2002 Rick Gaitskell Emission Lines

PH0008 Gaitskell Class Spring2002 Rick Gaitskell Corona Outermost layer of Sun is the Corona (“Crown”) o Requires eclipse (or coronagraph to observe) o Not sphereical Streamers/projections o Emission lines [see next] indicate hotter than Chromosph. Not just Fe + but Fe 13+ => T~2x10 6 o Intensity? (Flux ~  T 4 )

PH0008 Gaitskell Class Spring2002 Rick Gaitskell Corona in x-rays

PH0008 Gaitskell Class Spring2002 Rick Gaitskell Coronal Mass Ejection SOHO Satellite observation o C3 coronagraph (obs range solar corona radii) Coronal Mass Ejection o 18 Feb, 2000 (Medium Sized) o Follows onset of solar flare previous day (but not necessarily linked) o Takes ~2 days to arrive (this one is heading direct for Eath, hence “halo” like appearance o Up to 10 9 tonnes 0.01 c Like solar flares, they occur whenever there's a rapid, large-scale change in the sun's magnetic field. Solar flares and CMEs often occur together, but not necessarily because the flare triggers the CME or vice versa. One can happen without the other and frequently during solar maximum we see CMEs without an associated flare

PH0008 Gaitskell Class Spring2002 Rick Gaitskell SOHO Satellite observation (few hours prior to C3 movie) o C2 coronagraph (obs range solar corona radii)

PH0008 Gaitskell Class Spring2002 Rick Gaitskell Sun Spots And the Brightest and Hottest parts of Corona are… o …directly above another conspicuous feature: SUN SPOTS 4300K 5700K Photosphere 6300K [DEMO]

PH0008 Gaitskell Class Spring2002 Rick Gaitskell Differential Rotation of Sun Sun Spot Observation o Clear that different horizontal bands (latitudes) rotate at different rates Gallileo made first rot obs — (Live ~2 months) Richard Carrington, 1859 — Differential rotation Helioseismology o 1980’s able to determine how bulk is behaving 26 days 36 days

PH0008 Gaitskell Class Spring2002 Rick Gaitskell Sun Spot Cycle (# of Sun Spots & Position) 11 year cycle o i.e. ~11 years between max # o max -> min (no sun spots) -> max Position migrates over cycle o Min -> Starts ~30 deg lat o Max as moves toward equator o Next Min as Spots annihilate at equator [BOARD]

PH0008 Gaitskell Class Spring2002 Rick Gaitskell Zeeman Spliting of Abs. Lines in Sun Spots George Hale 1908 Permit determination of magnetic field strength and polarity

PH0008 Gaitskell Class Spring2002 Rick Gaitskell Magnetic-Dynamo Model (explain 22-year cycle) Horace Babcock 1960 o Proposes Magnetic-Dynamo Model to explain 22-year cycle (with polarity flips) o Makes use of Differential Rotation Convection See for dynamo discussion and figshttp://science.msfc.nasa.gov/ssl/pad/solar/quests.htm

PH0008 Gaitskell Class Spring2002 Rick Gaitskell Sun Spot Movie

PH0008 Gaitskell Class Spring2002 Rick Gaitskell Sun Spot Movie First part o Differential Rotation of Sun Spots o Sphere is then mapped onto sheet Second Part o Again see differential rotation Makes higher latitudes move slower than equator o Evolution of Sun Spots over 22 year cycle 1980 max — Top Hemisph: Yellow leads Blue — Bot Hemisph: Blue leads Yellow 1986 minima 1991 max (Poles Reversed) — Top Hemisph: Blue leads Yellow — Bot Hemisph: Yellow leads Blue 1997 minima

PH0008 Gaitskell Class Spring2002 Rick Gaitskell Solar Flares

PH0008 Gaitskell Class Spring2002 Rick Gaitskell Hydrostatic Equilibrium [DEMO - Balloons]

PH0008 Gaitskell Class Spring2002 Rick Gaitskell Regions of Sun What happens at radius~0.7? o Inside - radiation o Outside - convection T is low enough that neutral hydrogen forms o H absorbs visible light much better o Opacity increases o ->Convection

PH0008 Gaitskell Class Spring2002 Rick Gaitskell Summary Starting at the top… Corona (Flares/CME) o Very high temperature gas/plasma o Flares (hot ionized gas from sun spot) and CME (larger amounts of coronal gas) Chromasphere Photosphere (Sun Spots) o 400 km thick, 5800 K (Blackbody appears Yellow) o Sun spots show 22-year cycle (magnetic behaviour of Sun) Convection Zone [cell structure] Radiation Zone [r<0.7] Core (Fusion) [r<0.25] o Has it gone out, no! We see neutrinos! o But not as many as we expected…particle physics!

PH0008 Gaitskell Class Spring2002 Rick Gaitskell Did Not Cover in Lecture 19…

PH0008 Gaitskell Class Spring2002 Rick Gaitskell What is the Sun’s Source of Energy? Chemical Gravitational Infall? Fision? Fusion?

PH0008 Gaitskell Class Spring2002 Rick Gaitskell Solar Fusion Solar Core T~16x10 6 K

PH0008 Gaitskell Class Spring2002 Rick Gaitskell Solar Neutrinos Observed flux of electron neutrinos only ~1/3 that expected

PH0008 Gaitskell Class Spring2002 Rick Gaitskell Super-Kamiokande 20 stories high ~10 4 photo tubes 50 ktonnes of water

PH0008 Gaitskell Class Spring2002 Rick Gaitskell Image of Sun in Neutrinos ( ) Image from 500 days exposure… o 1km underground o Super-Kamiokande Experiment Angular scale o 90x90 degrees - what is angular scale of sun?

PH0008 Gaitskell Class Spring2002 Rick Gaitskell Extra Slides

PH0008 Gaitskell Class Spring2002 Rick Gaitskell Sun Profiles