Helios in Greek and Sol in Roman

Transcription

1 Helios in Greek and Sol in Roman Drove his chariot across the sky to provide daylight Returned each night in a huge golden cup on the river Oceanus His son Phaeton drove the chariot one day but lost control burning Africa and turning the Ethiopians black Japanese sun goddess Amatersasu emerges from her cave Ra and his barge

2 The Sun Radius is 100 times Earth s Rotates in ~25 days at Equator and ~40 days at poles Mass is 1,000 times Jupiter s mass. 1 Jupiter = 300 Earths Density = 1.4gm/cm 3 Surface Temperature 5780K

3 Lifetime of the Sun Sun radiates watts Burning oxygen and hydrogen sun lasts years Gravitational potential energy 30 million years But geologists and radioactive dates say billions of years

4 Hydrogen Fusion Powers the Sun Largest bomb USA made was 15 Megaton Bikini Atoll blast 1954 Nuclear (Strong force) is a million times the chemical (Electromagnetic force) 4 Hydrogen nuclei equal 1 Helium + energy

5 Binding Energy Fission produces energy by breaking up high mass nuclei Fusion produces energy by forming higher mass nuclei

6 Fusion Animation Protons repel each other since both have positive charge Coulomb barrier overcome by temperature of Millions Kelvin

7 Fusion Animation & Antiparticles Two protons make a deuterium ejecting a positron and a neutrino Neutrino escapes sun in seconds Positron is antielectron and annihilates an electron => gamma ray Every particle has an antiparticle When we make them we always get both anti-stars, anti-earths, anti?? A proton and a deuterium make a Helium 3 and a gamma ray Two Helium 3 s make a Helium nucleus and release two protons

8 Mass Disappears(?) 4 protons have more mass than 1 Helium 0.7% of input mass M becomes energy (m=0.007m) E=mc 2 with E in Joules, m in kg and c=3x10 8 m/sec Per second sun converts 600million tons of Hydrogen to Helium 4 million tons of mass to energy

9 Antiparticles - Positrons When a particle meets its antiparticle they annihilate Producing only energy = gamma rays Lucky for us the universe seems to be all matter

10 Ray Davis Solar Neutrino Detector Standard Model - four forces, four particles, three families, no gravity Average neutrino not stopped by a light year of lead First Neutrino detectors only found a third of the expected number Problem with sun?, neutrino detector?, neutrinos? Won Noble Prize in 2002 for NOT finding something

11 Sudbury Solar Neutrino Observatory Neutrinos oscillate from electron to muon to tau type

12 Components of Sun

13 Core, Radiation Zone, Convection Zone Heat/energy produced in hot dense core (15 million Kelvin) Transported by radiation initially and By convection after 70% of Radius By radiation from Photosphere to Earth

14 Core, Radiation, Convection Zones, Photosphere, Chromosphere, Corona Each gamma ray photon produced in core is absorbed and reemitted As possibly two or more lower energy photons Trip to surface takes ~million years One gamma ray becomes ~1800 visible photons

15 Photosphere - Sun with Giant Spots Effective temperature 5780K so sun is gaseous/plasma throughout Photosphere is apparent surface where hot gas becomes opaque H - Photosphere is 3400 times less dense than air on Earth 500km deep

16 Granulation Movie Granules are the top of convection cells About 1000km across

17 Granulation Model Granules last about 20 minutes Difference in temperature between center and edge is about 100K

18 3-D Sun, Near Edge Notice granules blocking each other s image Gas rises/falls with a speed of ~1km/sec

19 Supergranules & Limb Darkening 35,000 km across last about a day &contain ~300 granules Best seen in chromospheric network (bright circular areas) Edge of sun (limb) appears fainter than the center

20 Chromosphere in H-Alpha Thin layer above Photosphere ~1000km thick Filaments are dark & plage are bright regions Spectrum taken during eclipse shows emission lines - curves (chromo) and rings (corona)

21 Chromosphere and Venus Transit Temperature increases through chromosphere In transition region between Chromosphere and Corona temperature increases most quickly 10,000-1,000,000K

22 Spicules on Limb Spikes of gas rise 7000km through chromosphere They last ~5 minutes Seen here in H-Alpha

23 Corona in X-rays Corona heated to millions of degrees by flares?, spicules?,?? Photosphere emits few X-rays so it is dark Some other stars are bright in X-rays so they probably have a corona

24 Pearly White Corona Seen during a solar eclipse or with coronagraph Light scattered from dust and electrons - continuum Emission lines from highly ionized elements Very rarified and hot (Millions Kelvin)

25 Dark Coronal Holes Emit Solar Wind Solar Wind speed ~400km/sec and density ~7 protons/cm 3 Sun looses 10 million tons/year or solar masses

26 Helioseismology Solar surface moves up and down like ocean waves 5 minute oscillations were first of millions of modes to be discovered

27 Oscillation Modes Sound waves refracted back to surface Longer wavelengths reach further into sun Wavelength X Frequency = sound speed Sound speed gives temperature & density with depth

28 Differential Rotation Red fastest Blue slowest Left side shows rotation period is ~25 days at equator and ~40 days at poles Right side shows rotation in interior

29 The Active Sun Surface gas is electrically charged and moving So it generates magnetic fields Notice bright plage regions, filaments and prominence

30 Spot Motion and Evolution Spots last a few days to a month Big spots last longer Group of spots is called an active region

31 Sunspot Close-up Dark central region called umbra Temp~4000K Grey surrounding region is penumbra Temp~5000K

32 Sunspot at Various Heights in Sun From photosphere to a few hundred kilometers to chromosphere at few thousand km.

33 Under A Sunspot Spots are cooler due to deceased circulation Blocked energy is radiated from nearby regions

34 Latitude of Spot Appearance Spots first appear at +/-35 degrees latitude Appear closer to equator later in cycle Spots from new cycle can overlap with old cycle

35 Sunspot Number by Year More sunspots at maximum & sometimes none at minimum Number of spots varies with 11 year cycle Discovered by Schwabe in 1843

36 Solar Constant Solar irradiance more easily measured from above atmosphere A change of ~3% would start an ice age

37 Is the Solar Constant Constant? Lack of sunspots: called Maunder Minimum Coincides with Little Ice Age

38 Solar Constant / Sunspot Number Some stars exhibit brightness changes like rotation & spot cycles Ca H&K emission lines from active regions on other stars

39 Detecting a Sunspot s Magnetic Field Sunspots have magnetic field 1000 times Sun s average field, which is 1000 times Earth s magnetic field Magnetic fields are seen on some stars

40 Magnetic Polarity of Spots

41 Babcock Model Differential Rotation winds up field lines Which loop through the photosphere making a pair of spots Spots appear closer to equator during cycle Overall field reverses with 22 year cycle

42 Solar Flare Movie Flares can last from a few seconds to hours Seen in Visible, UV and X-Rays Also seen on other stars in Visible, UV and X-rays

43 3 rd Largest Solar Flare in X-rays 28 Oct 2003 Observed with EIT on SOHO Jupiter sized group in white light Visible to naked eye

44 3 rd Most Powerful Flare 28 Oct 2003 Frames ~30 min spacing Related Coronal Mass Ejection Noise caused by ejected protons X-rays seen from corona of other stars

45 Eruptive Prominence Over Half Hour Magnetically confined gas which is 70,000K

46 Flare and Eruptive Prominence

47 Coronal Mass Ejections

48 Heliosphere Solar wind is eventually stopped by interstellar medium

49 Solar Flares Affect Magnetosphere Solar flares and coronal mass ejections Impact Earth and guided by magnetic field Hit upper atmosphere and cause aurora

50 Sun-Earth-Aurora Connection Aurora forms oval surrounding magnetic pole Big storm big oval

51 Aurora Movie by Andre Clay in Alaska