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The Sun - challenge for scientists M.L. Khodachenko Institut für Weltraumforschung, Österreichische Akademie der Wissenschaften Graz, Austria Summer University, Graz in space 2006 – Sep. 7-8, 2006, Graz ¾ The Sun – our star ● Why do we study the Sun? ♦ The Sun is the nearest star: Many physical processes important for our understanding of the Universe can be observed and studied on the Sun. ♦ The Sun sustains the life on Earth, it A year (1992) of the Sun in soft X-rays (Yohkoh) 2 weeks during Jan. 2005. SOHO / MDI (~6,768 Å) controls terrestrial environment and impacts our technological civilization. ♦ The Sun is unique plasma physics laboratory of an astrophysical scale, close enough for precise measurements. SOHO/MDI magnetogram Sun in white light (HAO, Mauna Loa coronameter) Summer University, Graz in space 2006 – Sep. 7-8, 2006, Graz ¾ The Sun – our star Unsolved problems of the solar physics stimulate progress in the fundamental science, as well as in the technological and engineering branches. Summer University, Graz in space 2006 – Sep. 7-8, 2006, Graz ¾ The Sun – our star ● Two main focus areas of the modern solar science ♦ Understanding of the physical mechanisms of the solar dynamics and magnetism. Determination of ways by which the energy generated in the Sun’s core is released into space Detailed study of interaction of the solar plasmas and magnetic field. Theoretical analysis and modelling of the fundamental physical processes underlying the dynamic phenomena on the Sun should be combined with observations which are able to resolve scales and time intervals characteristic to these processes. ♦ Understanding and prediction of the geo-spheric and bio-spheric effects of the Sun Study of the solar activity phenomena and their manifestation in the heliosphere and the near Earth space, performed in close collaboration with life-sciences (biology, climatology, meteorology, ecology, etc.) Summer University, Graz in space 2006 – Sep. 7-8, 2006, Graz ¾ The Sun – our star The Sun – challenge for scientists Challenge to see Challenge to understand The main structure of the lection: ♦ What do we know (see and understand) about the Sun ? ♦ What is still the unclear (open questions) ? Summer University, Graz in space 2006 – Sep. 7-8, 2006, Graz ¾ The Sun – our star Hα 15,000 K He II, EUV 60,000 K Fe IX/X, EUV 1 MK UV 1600 Å 8000 K Magnetic field 5000 K Visible 5000 K Fe XII, EUV 1.5 MK Fe XIV, EUV 2 MK Broad window to the Sun Summer University, Graz in space 2006 – Sep. 7-8, 2006, Graz X-rays 4-6 MK ¾ The Sun : basic parameters Spectral type: G2 V (dwarf) Age: 4.5 billion years Diameter: 1,39 million km (108 Earth diameters) Mass: 1.99 x 1030 kg (333,000 Earth masses, or 99.9% of all matter in Solar System ) Luminosity: ~ 3.9 x 1026 W Temperature at Core: at surface: in Sunspots: Solar Cycle: 15 million K 5,700 K 4,000 K 8 - 11 years Summer University, Graz in space 2006 – Sep. 7-8, 2006, Graz ¾ The Sun : basic parameters Composition percentage of total number of atoms: 92.1% hydrogen (H) 7.8% helium (He) 0.1% other elements percentage of total mass: 74% hydrogen (H) 25% helium (He) 1% other elements Rotation Period (relative stars / relative Earth) at Equator: at Poles: ~ 25 / 27 Earth days ~ 30 / 32 Earth days Distance to Nearest Star: 4.3 light years Average Distance to Earth: 149,600,000 km (1AU) (147,100,000 km in January / 152,100,000 km in July) Summer University, Graz in space 2006 – Sep. 7-8, 2006, Graz ¾ Structure of the Sun : Inner regions ● Three main sections inside the Sun: ♦ Core – the innermost part of the Sun. - T= 15 million K - Occupies 1/50 of the solar volume, - Contains 1/2 of the whole solar mass - Generates 99% of the solar energy Summer University, Graz in space 2006 – Sep. 7-8, 2006, Graz ¾ Structure of the Sun : Inner regions ● Three main sections inside the Sun: ♦ Radiative zone (RZ) – the largest layer of the Sun (overlaps partially with the Core) -T ä from 15 million K to 2 million K - Outward transfer of energy by radiative diffusion - High opacity fi Multiple absorptions and re-emissions of photons (radiation diffusion time to the surface â up to 107 years) - Multiple collisions fi wavelength â from high-energy gamma-rays (in the core) to visible light (at the solar surface) Summer University, Graz in space 2006 – Sep. 7-8, 2006, Graz ¾ Structure of the Sun : Inner regions ● Three main sections inside the Sun: ♦ Convection zone – the outermost part of the Sun. - occurs at -T ä ~ (0.7 - 0.8) R from center from 2 million K to 6000 K - Material convection is dominating mechanism of energy transport - Energy reaches the surface mainly in the form of visible light. ♦ Altogether, across inner regions of the Sun - Temperature ä 3 ½ orders of magnitude (down to 6000 K) - Density ä 8 ½ orders of magnitude (down to 4 x 10-4 kg/m3) Summer University, Graz in space 2006 – Sep. 7-8, 2006, Graz ¾ Solar power supply : Nuclear fusion in the Core ● Extremely hot and dense plasma conditions in the solar Core : ♦ The temperature of 15 million K prevents the dense (160,000 kg/m3) core from reaching the solid state. ♦ High density and temperature fi nuclear fusion reactions fi energy release in the form of electromagnetic energy (gamma-rays) and energetic particles. Summer University, Graz in space 2006 – Sep. 7-8, 2006, Graz ¾ Solar power supply : Nuclear fusion in the Core ● Extremely hot and dense plasma conditions in the solar Core : ♦ The temperature of 15 million K prevents the dense (160,000 kg/m3) core from reaching the solid state. ♦ High density and temperature fi nuclear fusion reactions fi energy release in the form of electromagnetic energy (gamma-rays) and energetic particles. ● Hydrogen fusion cycle inside the Sun (proton-proton reaction) : involves: 4 Hydrogen nuclei (protons) and 2 electrons yields: Helium nucleus, 2 neutrinos and 6 photons 0.7 % of the Hydrogen supply mass turns into energy (typical for a main sequence star) Summer University, Graz in space 2006 – Sep. 7-8, 2006, Graz ¾ Solar power supply : Nuclear fusion in the Core ● Extremely hot and dense plasma conditions in the solar Core : ♦ The temperature of 15 million K prevents the dense (160,000 kg/m3) core from reaching the solid state. ♦ High density and temperature fi nuclear fusion reactions fi energy release in the form of electromagnetic energy (gamma-rays) and energetic particles. ● Hydrogen fusion cycle inside the Sun (proton-proton reaction) : involves: 4 Hydrogen nuclei (protons) and 2 electrons 1 + 2 e → 4He + 2 neutrinos + 6 photons Helium nucleus, 2 neutrinos and 6 photons yields: 4 H 0.7 % of the Hydrogen supply mass turns into energy (typical for a main sequence star) Summer University, Graz in space 2006 – Sep. 7-8, 2006, Graz ¾ Solar power supply : Nuclear fusion in the Core ● Extremely hot and dense plasma conditions in the solar Core : ♦ The temperature of 15 million K prevents the dense (160,000 kg/m3) core from reaching the solid state. ♦ High density and temperature fi nuclear fusion reactions fi energy release in the form of electromagnetic energy (gamma-rays) and energetic particles. ● Hydrogen fusion cycle inside the Sun (proton-proton reaction) : involves: 4 Hydrogen and electrons tons of He Every second 700,000,000 tonsnuclei of H is(protons) converted to 2695,000,000 and 4,900,000 tons of energy (E = mc2) Helium nucleus, 2 neutrinos and 6 photons yields: ⇓ 0.7 % of the Hydrogen supply mass turns into energy (typical for a main sequence star) Sun loses 4,900,000 tons of mass each second. Summer University, Graz in space 2006 – Sep. 7-8, 2006, Graz ¾ Solar power supply : Nuclear fusion in the Core ● Fusion reaction 4 1H + 2 e → 4He + 2 neutrinos + 6 photons goes in 3 steps 1. Fusion of Hydrogen into Deuterium : 1H + 1H → 2H + antielectron + neutrino 2 protons collide ⇓ proton 1 proton 2 antielectron → bounds to annihilates with neutron + antielectron + neutrino neutron → heavy Hydrogen (Deuterium) electron → 2 high-energy photons. Summer University, Graz in space 2006 – Sep. 7-8, 2006, Graz ¾ Solar power supply : Nuclear fusion in the Core ● Fusion reaction 4 1H + 2 e → 4He + 2 neutrinos + 6 photons goes in 3 steps 1. Fusion of Hydrogen into Deuterium : 1H + 1H → 2H + antielectron + neutrino 2 protons collide ⇓ proton 1 proton 2 antielectron → bounds to annihilates with neutron + antielectron + neutrino neutron → heavy Hydrogen (Deuterium) electron → 2 high-energy photons. Summer University, Graz in space 2006 – Sep. 7-8, 2006, Graz ¾ Solar power supply : Nuclear fusion in the Core ● Fusion reaction 4 1H + 2 e → 4He + 2 neutrinos + 6 photons 2. Formation of Helium-3 : 2H + 1H → 3He + photon Deuterium captures a proton ⇓ emittion of formination of photon 3He nucleus. Summer University, Graz in space 2006 – Sep. 7-8, 2006, Graz goes in 3 steps ¾ Solar power supply : Nuclear fusion in the Core ● Fusion reaction 4 1H + 2 e → 4He + 2 neutrinos + 6 photons 3. Recombination of Helium-3 into Helium : 3He + 3He → 4He + 1H+ 1H 2 Helium-3 recombine ⇓ emission of formination of 2 protons He nucleus. Summer University, Graz in space 2006 – Sep. 7-8, 2006, Graz goes in 3 steps ¾ Solar power supply : Nuclear fusion in the Core ● Fusion reaction 4 1H + 2 e → 4He + 2 neutrinos + 6 photons goes in 3 steps Reaction summary + 1H → 2H + antielectron + neutrino 1H + 1H → 2H + antielectron + neutrino electron + antielectron → photon + photon electron + antielectron → photon + photon 1H Step 1 Step 2 Step 3 + 1H → 3He + photon 2H + 1H → 3He + photon 2H 3He + 3He → 4He + 1H+ 1H ⇓ 6 1H + 2 e → 4He + 2 1H + 2 neutrinos + 6 photons net energy release is 26 MeV Summer University, Graz in space 2006 – Sep. 7-8, 2006, Graz ¾ Solar interior : Look under the surface ● Helioseismology: - Primary physics: wave motions excited and propagating in the solar interior - Sources of solar waves: processes in convection region (continuum source) - 3 kinds of waves in helioseismology: acoustic (p-modes), gravity (g-modes), surface gravity waves (f-modes) ♦ Sun acts as a resonant cavity: about 107 p- and f- modes - On the Sun's surface: waves appear Red / blue – opposite displacements f = 2935.88 +/- 0.2 microHz (SOHO/MDI) as up and down motions observed as Doppler shifts of spectrum lines Summer University, Graz in space 2006 – Sep. 7-8, 2006, Graz ¾ Solar interior : Look under the surface ● Helioseismology: ♦ Each oscillation mode is sampling different parts of the solar interior Periods of analyzed oscillations: ~ 1.5 min … ~ 20 min Wavelengths: 1000 km … 2 R Summer University, Graz in space 2006 – Sep. 7-8, 2006, Graz ¾ Solar interior : Look under the surface ● Helioseismology: ♦ L-nu Diagram – shows amount of acoustic energy per frequency for each spatial mode ℓ – angular degree = the number of node lines in a wave pattern at solar surface n – mode‘s order = number of radial nodes (different n → different curved lines) ♦ Most of the power (yellow) is concentrated in a band near 3 mHz (~ 5 min) Summer University, Graz in space 2006 – Sep. 7-8, 2006, Graz ¾ Solar interior : Look under the surface ● Time-distance helioseismology (with SOHO/MDI): Measure travel time for sound waves fi Sonogram image (subsurface structure of the sound speed) fi Temperature distribution & Subsurface Inhomogeneities = Acoustic tomography ♦ Temperature variation inside the Sun Summer University, Graz in space 2006 – Sep. 7-8, 2006, Graz ¾ Solar interior : Look under the surface ● Time-distance helioseismology (with SOHO/MDI): ♦ Subsurface flows of gas measured by SOHO/MDI convection flows motion from the equator towards the poles Summer University, Graz in space 2006 – Sep. 7-8, 2006, Graz ¾ Solar interior : Look under the surface ● Time-distance helioseismology (with SOHO/MDI): ♦ Difference in speed between various areas on the Sun (SOHO/MDI) Change of the time averaged rotation rate on/in the Sun red – faster then average blue – slower then average Summer University, Graz in space 2006 – Sep. 7-8, 2006, Graz ¾ Solar interior : Look under the surface ● Time-distance helioseismology (with SOHO/MDI): ♦ Difference in speed between various areas on the Sun (SOHO/MDI) Rotation rate of the solar sphere: Orange – rotation of the bulk of the Sun (~30 degrees latitude) Red – faster than average rotation Yellow / blue – slower than average rotation Summer University, Graz in space 2006 – Sep. 7-8, 2006, Graz ¾ Solar interior : Look under the surface ● Time-distance helioseismology (with SOHO/MDI): ♦ Difference in speed between various areas on the Sun (SOHO/MDI) Depth and latitude variation of the solar rotation rate: - The inner 70% of the Sun rotates at nearly the same rate - Differential rotation in the outer 30% of the Sun (in convection zone) Summer University, Graz in space 2006 – Sep. 7-8, 2006, Graz ¾ Solar interior : Look under the surface ● Time-distance helioseismology (with SOHO/MDI): ♦ Difference in speed between various areas on the Sun (SOHO/MDI) Depth and latitude variation of the solar rotation rate: - Change in rotation rate with depth, in a very thin layer just under the surface - yellow line - Jet-stream at about 75 degrees latitude and about 45,000 km below the surface Summer University, Graz in space 2006 – Sep. 7-8, 2006, Graz ¾ Solar interior : Look under the surface ● Time-distance helioseismology (with SOHO/MDI): ♦ Difference in speed between various areas on the Sun (SOHO/MDI) Spatial and temporal variation of the solar rotational flows speed red – faster then average blue – slower then average Summer University, Graz in space 2006 – Sep. 7-8, 2006, Graz ¾ Solar interior : Look under the surface ● Time-distance helioseismology (with SOHO/MDI): ♦ Difference in speed between various areas on the Sun (SOHO/MDI) Speed change measurements give more details on the structure and dynamics of the solar surface and sub-surface flows - Jet-stream at about 75 degrees latitude and about 45,000 km below the surface Summer University, Graz in space 2006 – Sep. 7-8, 2006, Graz ¾ Solar interior : Look under the surface ● Time-distance helioseismology (with SOHO/MDI): ♦ Difference in speed between various areas on the Sun (SOHO/MDI) - Jet-stream at about 75 degrees latitude and about 45,000 km below the surface Summer University, Graz in space 2006 – Sep. 7-8, 2006, Graz ¾ Solar atmosphere : Photosphere ● Photosphere – the most dense part of the solar atmosphere (0.02 g/m3) - 550 km thick layer in which the solar material changes from being completely opaque (to radiation) to being transparent. Visible surface of the Sun. - the layer which emits most of the solar energy (in white light) - one of the coolest regions of the Sun (6000 K) fraction (0.1% ) of the gas is ionized - Photospheric minimum: T ~ 4200 K (at 550 km above the surface) fi only a small Summer University, Graz in space 2006 – Sep. 7-8, 2006, Graz ¾ Solar atmosphere : Photosphere ● View in white-light: a disk with dark spots. Summer University, Graz in space 2006 – Sep. 7-8, 2006, Graz ¾ Solar atmosphere : Photosphere ● Photospheric Convection / granulation Maretial convection inside the Sun fi granulation pattern on the solar surface ♦ Granulation parameters: - Size of granula: 700-1500 km - Average granula life time: ~10 min - Convection velosity: 0.2 - 0.5 km/s ♦ Super-ganulation: organized granula clusters (20,000 – 30,000 km) Summer University, Graz in space 2006 – Sep. 7-8, 2006, Graz ¾ Solar atmosphere : Photosphere ● Photospheric Convection / granulation ♦ Numeric simulation of solar convection on super-computers There is still a lot of work to include all the appropriate physics into the numerical models Summer University, Graz in space 2006 – Sep. 7-8, 2006, Graz ¾ Solar atmosphere : Photosphere ● Sunspots – the sites of strong magnetic fields (2000-5000 G) - Low temperature of sunspots (~ 4000 K) is due to strong magnetic field which promotes material cooling fi dark appearance on the photospheric background (~ 6000 K) - Size: ~1500 km – 50000 km in diameter - Structure: umbra, penumbra Summer University, Graz in space 2006 – Sep. 7-8, 2006, Graz ¾ Solar atmosphere : Photosphere ● Sunspots – the sites of strong magnetic fields (2000-5000 G) - Low temperature of sunspots (~ 4000 K) is due to strong magnetic field which promotes material cooling fi dark appearance on the photospheric background (~ 6000 K) - Size: ~1500 km – 50000 km in diameter - Structure: umbra, penumbra Summer University, Graz in space 2006 – Sep. 7-8, 2006, Graz ¾ Solar atmosphere : Photosphere ● Complex dynamics and evolution of sun spots - Appearance / disappearance by successive fragmentation into smaller elements (formation: days – weeks; life time: weeks – months) - Rotation - Mutual interactions SOHO/MDI Mar. – May 2001 Summer University, Graz in space 2006 – Sep. 7-8, 2006, Graz ¾ Solar atmosphere : Photosphere ● Complex dynamics and evolution of sun spots - Appearance / disappearance by successive fragmentation into smaller elements (formation: days – weeks; life time: weeks – months) - Rotation - Mutual interactions Sun spot birth TRACE (white light) Jul. 27- Aug. 06, 2001 Summer University, Graz in space 2006 – Sep. 7-8, 2006, Graz ¾ Solar atmosphere : Photosphere ● Magnetograph measurements of solar magnetic fields at the photosphere ♦ Full disk magnetograms – monitoring of sunspots and large-scale m. fields - Sunspots are usually grouped in pairs of opposite magnetic polarities - Sunspots are confined to low latitudes (< 40 degrees) - Sunspots pairs tend to line up in the East-West direction and drift towards higher latitudes - Magnetic polarities of sunspot pairs in the northern and southern solar hemispheres are reversed (Hale’s law) SOHO MDI magnetogram Light – south polarity; Dark – north polarity Summer University, Graz in space 2006 – Sep. 7-8, 2006, Graz ¾ Solar atmosphere : Photosphere ● Magnetograph measurements of solar magnetic fields at the photosphere ♦ Full disk magnetograms – monitoring of sunspots and large-scale m. fields - Sunspots are usually grouped in pairs of opposite magnetic polarities - Sunspots pairs tend to line up in the East-West direction and drift towards higher latitudes - Magnetic polarities of sunspot pairs in the northern and southern solar hemispheres are reversed (Hale’s law) Light – south polarity; Dark – north polarity Summer University, Graz in space 2006 – Sep. 7-8, 2006, Graz ¾ Solar atmosphere : Photosphere ● Magnetograph measurements of solar magnetic fields at the photosphere ♦ Full disk magnetograms – monitoring of sunspots and large-scale m. fields - Each next sunspot cycle, magnetic polarities of the sunspot pairs undergo a reversal fi full solar cycle is ~ 22 years Summer University, Graz in space 2006 – Sep. 7-8, 2006, Graz ¾ Solar atmosphere : Photosphere ● Magnetograph measurements of solar magnetic fields at the photosphere ♦ High resolution magnetograms – study of dynamics of small-scale m. fields Magnetic carpet Light – south polarity Dark – north polarity SOHO/MDI Numeric simulations Summer University, Graz in space 2006 – Sep. 7-8, 2006, Graz ¾ Solar atmosphere : Photosphere ● Origin and development of sunspots ♦ Solar dynamo: stretch of the magnetic field lines by differential rotation ♦ Magnetic buoyancy Summer University, Graz in space 2006 – Sep. 7-8, 2006, Graz ¾ Solar atmosphere : Photosphere ● Origin / development of sunspots Artist concept of magnetic flux emergence Numeric simulation of magnetic flux emergence (Naval Research Laboratory, USA) Summer University, Graz in space 2006 – Sep. 7-8, 2006, Graz ¾ Solar atmosphere : Photosphere ● 3-D structure of sun spots – subsurface temperature profile (with SOHO/MDI): Blue Red – cooler then average; – warmer then average Magnetic field blocks the Higher temperatures below the surprisingly shallow (just ~6000temperatures km) flowsSunspots that carryare heat up fi blockage and cooler from the solar interior above. Summer University, Graz in space 2006 – Sep. 7-8, 2006, Graz ¾ Solar atmosphere : Photosphere ● Subsurface structure and material circulation in sunspots (with SOHO/MDI): Blue – cooler then average; Red – warmer then average Strong m. fields promote cooling fi Cool material sinks down (speed up to 6000 km/h) fi Inward flow, holding the sunspot together (while m.field is strong enough) Summer University, Graz in space 2006 – Sep. 7-8, 2006, Graz ¾ Solar atmosphere : Photosphere ● Monitoring of sun spots behind visible solar disk spots ♦ sonogram imaging of the solar far side Important for the tasks of forecasting of sunspots appearance on the Earth directed side of the Sun ⇓ Space Weather Summer University, Graz in space 2006 – Sep. 7-8, 2006, Graz ¾ Solar atmosphere : Chromosphere ● Chromosphere – the layer of the solar atmosphere located above the photosphere and beneath the corona - ~ 2500 kilometers thick layer - appears as a thin reddish ring prior and just after the peak of a total solar eclipse - slow â of T from 4300 K to 104 K at heights 550-1700 km and sharp â from 104 K to 3x105 K at ~ 50 km interval near 2000 km fi Transition region - Strongly inhomogeneous: cold (~104 K) structures co-exist with hot (~106 K) plasmas Summer University, Graz in space 2006 – Sep. 7-8, 2006, Graz ¾ Solar atmosphere : Chromosphere ● Most easily chromosphere is viewed in emission lines: H-alpha, Ca K, UV (He II) ♦ Chromosphere in H-alpha (λ = 6563 Å) : - bright regions – plages, actve regions - dark features - filaments (prominences) H-alpha image (NSO at Sacramento Peak) Sun in H-alpha (1/1/95-4/9/95) (HAO, Mauna Loa Solar Obs.) Summer University, Graz in space 2006 – Sep. 7-8, 2006, Graz ¾ Solar atmosphere : Chromosphere ● Most easily chromosphere is viewed in emission lines: H-alpha, Ca K, UV (He II) ♦ Chromosphere in Ca K (λ = 3933 Å) : - magn. sensitivity of Ca K line ⇓ contrast between magn. active regions and the rest of the solar surface - features of the solar disk seen in white light remain visible ⇓ sunspots can be seen - plages (faculae) appear as bright Ca K image (NSO) areas surrounding the sunspot groups (associated with regions of ~100G m.field) Summer University, Graz in space 2006 – Sep. 7-8, 2006, Graz ¾ Solar atmosphere : Chromosphere ● Most easily chromosphere is viewed in emission lines: H-alpha, Ca K, UV (He II) ♦ Chromosphere in Ca K (λ = 3933 Å) : High solar activity - Mar. 28, 2001 (NASA/GSFC) Moderate solar activity - Apr. 27, 2002 (NASA/GSFC) Low solar activity - Oct.28, 1998 (NASA/GSFC ) ♦ hotter than sunspots faculae contribute to increasing the solar flux Summer University, Graz in space 2006 – Sep. 7-8, 2006, Graz ¾ Solar atmosphere : Chromosphere ● Most easily chromosphere is viewed in emission lines: H-alpha, Ca K, UV (He II) ♦ Chromosphere in UV: He I (λ = 584,3 Å), He II line (λ = 304 Å) Sun in He I line (upper chromosphere: 2 x 104K) SOHO/SUMMER Sun in He II line (upper chromosphere: 6 x 104K) SOHO/EIT Summer University, Graz in space 2006 – Sep. 7-8, 2006, Graz ¾ Solar atmosphere : Chromosphere ● Most easily chromosphere is viewed in emission lines: H-alpha, Ca K, UV (He II) ♦ The sources of EUV radiation in the Transition region (T ~ 2.5 x 105 K) are connected to the chromospheric parts of magnetic loops Correlation of location of the EUV emission sources in transition region and the photospheric magnetic fields SOHO/MDI/CDS Summer University, Graz in space 2006 – Sep. 7-8, 2006, Graz ¾ Solar atmosphere : Chromosphere ● On the limb: jets of plasma shooting up from supergranule boundaries – Spicules Spicules (Big Bear Observatory) - Diameter: 500-1200 km - Height: 10000-15000 km - Temperature: (1..2) x 104 K - Material upward speed: 20-30 km/s - Life-time: 5 - 10 min ♦ Macro-spicules in polar regions of open m.field - Diameter: 4000-11000 km - Height: 4000-40000 km - Material upward speed: 10-150 km/s - Life-time: 8 - 45 min Summer University, Graz in space 2006 – Sep. 7-8, 2006, Graz ¾ Solar atmosphere : Corona ● Corona – the outermost layer of the solar atmosphere visibility only during solar Small density (108 cm-3); fi higher transparency fi eclipses (natural/artificial) i.e. when light from the decrease with distance than the inner layers photosphere is blocked - Temperature > 1 x 106 K (200 times hotter Nov.3, 1993, Bolivia (Fred Espenak) than the Sun‘s surface) - Coronal heating mechanism is still in question (should be connected with complex m.fields and related phenomena: flares; electr.currents; waves) Summer University, Graz in space 2006 – Sep. 7-8, 2006, Graz ¾ Solar atmosphere : Corona magnetogram based reconstruction ● Coronal structure elements: - coronal loops - streamers (up to 10 R) with 3-10 times higher density SOHO/LASCO: Solar corona in 05-07/1996 3-D reconstruction of solar corona - coronal holes (open m.field line regions) → fast solar wind Summer University, Graz in space 2006 – Sep. 7-8, 2006, Graz ¾ Solar atmosphere : Corona ● The heat and energy release in the corona cause its soft X-rays, UV radiation ♦ Solar corona in soft X-rays: - Dark areas – coronal holes (above poles) - Bright X-ray regions – T > 2 x 106 K (typical in active regions, near sunspots) - Flares – short increases in brightness Yohkoh X-ray image - Streamers are connected to large active regions (sunspot groups) - coronal holes are dark in white light because of lower gas densities White-light (Mauna Loa Solar Obs.) and soft X-ray (Yohkoh) Summer University, Graz in space 2006 – Sep. 7-8, 2006, Graz ¾ Solar atmosphere : Corona ● The heat and energy release in the corona cause its soft X-rays, UV radiation ♦ Solar corona in EUV : - Fe XII line (195 Å): Corresp. temperature: ~ 1.5 x 106 K SOHO/EIT movie - active regions are seen as bright; - flares followed by proton shower - coronal holes SOHO/EIT movie Summer University, Graz in space 2006 – Sep. 7-8, 2006, Graz ¾ Solar atmosphere : Corona ● The heat and energy release in the corona cause its soft X-rays, UV radiation ♦ Solar corona in EUV : - Composite view in 3 wavelengths: Fe IX/X (171 Å) blue: ~ 1.0 x 106 K Fe XII (195 Å) green: ~ 1.5 x 106 K Fe XIV (284 Å) orange: ~ 2.0 x 106 K - active regions - hot coronal loops - coronal holes Summer University, Graz in space 2006 – Sep. 7-8, 2006, Graz ¾ Solar atmosphere : Corona ● The heat and energy release in the corona cause its soft X-rays, UV radiation ♦ Extended solar corona (above 1.25 R) in UV : - Outer corona in 3-D - Helmet streamer (~ 3 x 106 km) in - Lyman-alpha (atomic Hydrogen) - Oxygen VI combined UV/EUV observations (SOHO: UVCS / EIT) Summer University, Graz in space 2006 – Sep. 7-8, 2006, Graz ¾ Solar atmosphere : Corona ● The heat and energy release in the corona cause its soft X-rays, UV radiation ♦ Solar corona in EUV / UV : - Composite UV image the Sun's extended corona: SOHO/UVCS (outside black circle) SOHO/EIT (inside circle). ♦ Recent finding: Protons and the more massive ions (oxygen, magnesium etc.) are hotter than the electrons in the outflowing coronal gas. Preferential heating and acceleration of heavy particles may be due to absorption of high frequency MHD waves. Summer University, Graz in space 2006 – Sep. 7-8, 2006, Graz ¾ Solar atmosphere : Corona ● Coronal holes (CH) in white light and X-rays and EUV/UV lower gas densities in CH less heating in CH dark appearance of CH in white light (as compared to bright helmet streamers) dark appearance of CH in X-rays and EUV/UV › › › › › › › › › › › › CH are regions of open magnetic field lines fi easy and fast outflow of coronal gas (as solar wind) along the field lines. In helmet streamers the coronal material is trapped by the closed magnetic field lines fi enhanced densities fi detectable levels of X-ray emission Summer University, Graz in space 2006 – Sep. 7-8, 2006, Graz ¾ Solar atmosphere : Corona ● Coronal loops (CL) – one of the main structural elements of the solar atmosphere ♦ 5 Types of CLs (observed in X-rays & EUV): - Active region (AR) loop – part of an AR structure L ~ (10-100)x103 km; T ~ 104-2.5x106 K; n ~ (0.5-5.0)x109 cm-3 - Quite region loop – not related to an AR L ~ (20-700)x103 km; T ~ 1.8x106 K; n ~ (0.2-1.0)x109 cm-3 - Connecting loop – link different ARs SOHO/EIT: EUV L ~ (20-700)x103 km; T ~ (2-3)x106 K; n ~ 7x108 cm-3 - Flare loop L ~ (5-50)x103 km; T ≤ 4x107 K; n ≤ 1012 cm-3 - Post-flare loop L ~ (10-100)x103 km; T ~ 104-4x106 K; n ~ 1011 cm-3 Summer University, Graz in space 2006 – Sep. 7-8, 2006, Graz Yohkoh: X-ray ¾ Solar atmosphere : Corona ● Coronal loops (CL) – one of the main structural elements of the solar atmosphere 1. Active region (AR) loop – part of an AR structure L ~ (10 - 100) x 103 km T ~ 104 - 2.5 x 106 K n ~ (0.5 - 5.0) x 109 cm-3 ♦ AR loops with different T: He I: 2 x 104 K O V: 2.5 x 105 K Mg IX: 106 K Si XII: 2 x 106 K SOHO/CDS Summer University, Graz in space 2006 – Sep. 7-8, 2006, Graz ¾ Solar atmosphere : Corona ● Coronal loops (CL) – one of the main structural elements of the solar atmosphere 2. Quite region loop – not related to an AR TRACE (171Å), May 5, 1998 L ~ (20 - 700) x 103 km T ~ 1.8 x 106 K n ~ (0.2 - 1.0) x 109 cm-3 ♦ Quiet corona and limb loops observed by TRACE (171Å) Summer University, Graz in space 2006 – Sep. 7-8, 2006, Graz ¾ Solar atmosphere : Corona ● Coronal loops (CL) – one of the main structural elements of the solar atmosphere 3. Connecting loop – link different ARs L ~ (20 - 700) x 103 km T ~ (2 - 3) x 106 K n ~ 7 x 108 cm-3 ♦ 2 days of development of connecting loops seen by SOHO/EIT: Fe XII (195Å): 1.5x106 K Summer University, Graz in space 2006 – Sep. 7-8, 2006, Graz ¾ Solar atmosphere : Corona ● Coronal loops (CL) – one of the main structural elements of the solar atmosphere 4. Flare loop L ~ (5 - 50) x 103 km T ≤ 4 x 107 K n ≤ 1012 cm-3 X-ray M1 flare, May 16, 1999,TRACE (171Å) X-ray M2 flare, May 10, 1999, TRACE (171Å) Summer University, Graz in space 2006 – Sep. 7-8, 2006, Graz ¾ Solar atmosphere : Corona ● Coronal loops (CL) – one of the main structural elements of the solar atmosphere 5. Post-flare loop L ~ (10 - 100) x 103 km T ~ 104 – 4 x 106 K n ~ 1011 cm-3 ♦ Post-flare loops observed by TRACE on the disk: flare on 14.07.2000 (195Å) („Bastille Day flare“) on the limb: flare on 15.04.2001 (171Å) Summer University, Graz in space 2006 – Sep. 7-8, 2006, Graz ¾ Solar atmosphere : Corona ● Coronal loops (CL) – one of the main structural elements of the solar atmosphere ♦ Hot plasma tends to flow along the magnetic field lines, making the CLs to be visible in X-rays & EUV corresponding to high temperatures CLs observed in EUV (by TRACE) Summer University, Graz in space 2006 – Sep. 7-8, 2006, Graz ¾ Solar atmosphere : Corona ● Coronal loops (CL) – one of the main structural elements of the solar atmosphere ♦ Hot plasma tends to flow along the magnetic field lines, creating the CLs which are visible in X-rays & EUV corresponding to high temperatures CLs observed in EUV (by TRACE) Summer University, Graz in space 2006 – Sep. 7-8, 2006, Graz ¾ Solar atmosphere : Corona ● Coronal loops (CL) – one of the main structural elements of the solar atmosphere ♦ 3-D reconstruction of the solar CLs structure based on magnetogram and EUV (SOHO/MDI/EIT) data: Magnetogram data were processed through the Potential Field Source Surface (PFSS) model which constructs the magnetic field above the solar surface. Summer University, Graz in space 2006 – Sep. 7-8, 2006, Graz ¾ Solar atmosphere : Corona ● Solar prominences or filaments (when observed on the disk) ♦ Cold and dense (as compared to surrounding plasma) condensations of coronal material supported by the magnetic field Typical values: T ~ 5000 – 10000 K n ~ 1010 – 1011 cm-3 ⇓ Visible in H-alpha on the limb: bright on the disk: dark H-alpha image (NOAA, Aug. 1980) ♦ Two different types of the solar prominences: - Quiescent prominence - Active prominence Summer University, Graz in space 2006 – Sep. 7-8, 2006, Graz ¾ Solar atmosphere : Corona ♦ Quiescent prominence (quiet filament) – very stable and long living object (usually located along the magnetic neutral line) Life-time: up to several months Temperature: 5000 – 8000 K Density: 1010 – 1011 cm-3 Length: 6 x 104 – 106 km TRACE (171Å), May 21, 1998 Height: 1.5 x 104 – 105 km Thickness: 4000 – 1.5 x 104 km Magnetic field: ≤ 40 G Summer University, Graz in space 2006 – Sep. 7-8, 2006, Graz ¾ Solar atmosphere : Corona ♦ Quiescent prominence (quiet filament) – very stable and long living object (usually located along the magnetic neutral line) Dancing prominences (TRACE 171 Å, Jul. 27, 1998) Summer University, Graz in space 2006 – Sep. 7-8, 2006, Graz ¾ Solar atmosphere : Corona ♦ Quiescent prominences tend to form along the boundaries between regions of opposite magnetic polarity, i.e. along the magnetic neutral line The fact that filaments are usually aligned with magnetic neutral lines strongly suggests that magnetic fields are responsible for supporting filaments against the gravity. Summer University, Graz in space 2006 – Sep. 7-8, 2006, Graz ¾ Solar atmosphere : Corona ♦ Support of a quiescent prominence against gravity: Prominence fibrils are confined in the dipped top part of a magnetic arcade Summer University, Graz in space 2006 – Sep. 7-8, 2006, Graz ¾ Solar atmosphere : Corona ♦ Active prominence – dynamical object with intensive motion of material (located in active regions and usually connected with solar flares) Life-time: minutes – hours Temperature: 10000 – 80000 K Density: ≥ 1011 cm-3 Filament eruption (SOHO/EIT: 195Å) Height: TRACE, 171Å, Jul.19, 2000 1.5 x 104 – 2 x 105 km Magnetic field: ≤ 100 – 200 G Summer University, Graz in space 2006 – Sep. 7-8, 2006, Graz ¾ Solar atmosphere : Corona ♦ Activation of prominences → Eruptive prominences - Increase of the size and brightness - Increase of material flow speed fi - Oscillations (T ~ 6 – 40 min) Prominence oscillations after flare material eruption (up to 100 km/s) Eruptive prominences observed by SOHO/EIT, He II line (304Å): 60000 – 80000 K Summer University, Graz in space 2006 – Sep. 7-8, 2006, Graz ¾ Solar atmosphere : Corona ♦ Activation of prominences → Eruptive prominences Eruptive prominences observed by SOHO/EIT, He II line (304Å): 60000 – 80000 K Summer University, Graz in space 2006 – Sep. 7-8, 2006, Graz ¾ Solar atmosphere : Corona ♦ Activation of prominences → Eruptive prominences Eruption of a prominence observed by SOHO/EIT in He II line (304Å) The whole process took 3 hours Summer University, Graz in space 2006 – Sep. 7-8, 2006, Graz ¾ Solar atmosphere : Corona ♦ Activation of quiescent prominences – development of an instability in a filament, “disparition brusque” - Filament lifts up as an eruptive prominence and completely disappears. - The whole process takes from several min to several hours. - Brightness increase in X-rays and H-alpha → flare Summer University, Graz in space 2006 – Sep. 7-8, 2006, Graz ¾ Solar atmosphere : Corona ♦ Activation of quiescent prominences – development of an instability in a filament, “disparition brusque” Filament eruption with formation of a set of hot, bright, activated coronal loops (500,000 – 2,000,000 K) Oct. 20, 1999 TRACE (195Å) SOHO/EIT, He II line (304Å): 60000 – 80000 K Summer University, Graz in space 2006 – Sep. 7-8, 2006, Graz ¾ Solar atmosphere : Corona ● Solar corona is a non-stationary, dynamic object: - Magnetic loops - Filaments & Prominences - Flares, Eruptions - Coronal Mass Ejections (CMEs) Long-time evolution of active regions dynamics of coronal structures The corona extends outward as solar wind Summer University, Graz in space 2006 – Sep. 7-8, 2006, Graz ¾ Solar phenomena : Solar flares ● Solar Flare – rapid release of energy from a localized region on the Sun in the form of electromagnetic radiation, energetic particles, and mass motions. - sudden, localized, transient increases in brightness occurred in active regions near sunspots - most easily seen in H-alpha and X-rays, but have also effects in all the elecromagnetic spectrum Flare in H-alpha Flare in EUV (171 Å)TRACE Summer University, Graz in space 2006 – Sep. 7-8, 2006, Graz ¾ Solar phenomena : ● Energy release of solar flare: Solar flares 1029 – 3 x 1032 erg ♦ Distribution of energy in solar flare: - Electromagnetic radiation (up to X-ray): 35 % - Interplanetary shock wave: 35 % - Energetic electrons (hard X-ray): 15 % - Sub-relativistic protons: 6 % - Relativistic protons: 9 % ♦ Energy source – the solar magnetic field Annihilation of 500 G magnetic field in a 30000 x 30000 x 30000 km cube „Bastille Day flare“ in EUV (TRACE, Jul. 14, 1998) 3 x 1032 erg Details of the flaring energy release mechanism are still a puzzle Summer University, Graz in space 2006 – Sep. 7-8, 2006, Graz ¾ Solar phenomena : ● 3 different phases of a typical Solar flares solar flare: observed in electromagnetic and particle radiation (from Kane 1974) Precursor ~5-10 min (before) Impulsive phase ~2 - 5 min Extended phase - Flash phase - Main phase (~10 min + ~1 h) Summer University, Graz in space 2006 – Sep. 7-8, 2006, Graz ¾ Solar phenomena : Solar flares ● Indication of physical processes in flaring phenomena: ● Presence of energetic particle fluxes ● Indication of running shock waves ● Presence of hot plasma clouds ¾ Solar phenomena : Solar flares ● Development and structure of solar flares ♦ Trigger of flare – emergence of a new magnetic flux ♦ Two types of flares: 1. Simple loop flare (compact flare) - increase of brightness of a separate loop - one pulse of X-rays (~ 1 min) - main energy release in an impulsive phase - high temperature (~ 3 x 107 K) kernel 1500 – 4000 km in the top of the loop - whole duration ~ 1-2 hours Loop flare in EUV (TRACE) Summer University, Graz in space 2006 – Sep. 7-8, 2006, Graz ¾ Solar phenomena : Solar flares ● Development and structure of solar flares ♦ Trigger of flare – emergence of a new magnetic flux ♦ Two types of flares: 2. Two-ribbon flare – large flare - eruption of filament (begins 10-60 min before the flash phase) - Flash phase: formation of two bright ribbons – footpoints of flaring magnetic arcade - bright post-flare loops - whole duration several hours flare in EUV (TRACE) Summer University, Graz in space 2006 – Sep. 7-8, 2006, Graz ¾ Solar phenomena : Solar flares ● Development and structure of solar flares Combined observations (AR10720) – simultaneous TRACE & RHESSI imagery RHESSI: gamma-rays (blue) – energetic protons. High-energy emission marks the footpoints of coronal loops X-rays (red) – the hottest part of flare. Emission from the loop structure TRACE: UV images Flare ribbons - multiple hot-spots at the loop footpoints Summer University, Graz in space 2006 – Sep. 7-8, 2006, Graz ¾ Solar phenomena : Solar flares ● Development and structure of solar flares Theoretical model: Primary energy release in the corona Particle acceleration Collisional interaction of fast electrons with a background plasma • thick-target bremsstrahlung • heating of the low chromosphere to soft X-ray emitting temperatures • creation of steep pressure gradients resulting in material upflows Summer University, Graz in space 2006 – Sep. 7-8, 2006, Graz ¾ Solar phenomena : Solar flares ● Development and structure of solar flares Simultaneous obstervations of “Bastille Day flare” (Jul. 14, 2000): by SOHO (EUV + Coronographs) TRACE (close up EUV) and Summer University, Graz in space 2006 – Sep. 7-8, 2006, Graz ¾ Solar phenomena : Solar flares ● Long-distance (heliospheric) effects of solar flares: Multi instrument & multi spacecraft observations of solar flares in Oct-Nov. 2003: SOHO: EUV + Coronographs (C2,C3) SORCE: (X-ray photometry ) Record-breaking solar flares in the Fall of 2003: ● X17 flare on Oct. 28, 2003 ● X11 flare on Oct. 29, 2003 ● X28 flare on Nov. 4, 2003 Summer University, Graz in space 2006 – Sep. 7-8, 2006, Graz ¾ Solar phenomena : Coronal Mass Ejections ● Coronal Mass Ejection (CME) – a huge cloud of plasma that erupts from the Sun's corona and travels through space (in the solar wind) at high speed - High speed (~ 200-2000 km s-1); - Intrinsic magnetic field; - Billions of tons of material ⇒ Significant disturbances in Interplanetary medium ♦ CMEs are considered as critical element of solar dynamo Summer University, Graz in space 2006 – Sep. 7-8, 2006, Graz ¾ Solar phenomena : Coronal Mass Ejections ● Origin of CMEs, Relation to flares - CMEs are associated with flares and prominence eruptions - CME source location: active regions (groups of sunspots), prominence sites (not only in active regions) Summer University, Graz in space 2006 – Sep. 7-8, 2006, Graz ¾ Solar phenomena : Coronal Mass Ejections ● Origin of CMEs, Relation to flares CME originate from closed magnetic field regions on the Sun ⇓ Presence of a closed magnetic field structure – basic characteristic of CME Producing regions Summer University, Graz in space 2006 – Sep. 7-8, 2006, Graz ¾ Solar phenomena : Coronal Mass Ejections ● Origin of CMEs, Relation to flares Probability of CME–flare association increases with a duration of a flare: ~ 26% for duration < 1 h 100% for duration > 6 h Summer University, Graz in space 2006 – Sep. 7-8, 2006, Graz ¾ Solar phenomena : Coronal Mass Ejections ● Origin of CMEs, Relation to flares There is a physical link between flares and CMEs (yet poorly known...) Common-cause scenario: falres and CMEs are manifestations of the same large-scale magnetic process Summer University, Graz in space 2006 – Sep. 7-8, 2006, Graz ¾ Solar phenomena : Coronal Mass Ejections ● Multi-thermal structure of CMEs - coronal material in the front region (~ 2 MK) - prominence material (~8000 K), or hot flare plasma (~10 MK) ♦ CME with an ordered magnetic field → Magnetic Cloud (MC) Summer University, Graz in space 2006 – Sep. 7-8, 2006, Graz ¾ Solar phenomena : ● Parameters of CMEs: Coronal Mass Ejections speed - Tracking a CME feature ⇒ vCME from tens km/s to > 2500 km/s (average vCME 489 km/s ) - Annaual average vCME has a tendency to increase towards solar maximum (Yashiro, et al., Adv. Space Res., 32, 2631, 2003) Summer University, Graz in space 2006 – Sep. 7-8, 2006, Graz ¾ Solar phenomena : ● Parameters of CMEs: Coronal Mass Ejections size - angular width ΔCME increases in the beginning (< 5 RSun ) of propagation - Annual average widths of CMEs range from 45° (solar minimum) to 61° (close before activity maximum) ● Parameters of CMEs: density - No direct measurements of nCME close to the Sun (< 30 Rsun = 0.14 AU) - Analysis of CMEs brightness in the white-light (Thomson scattering) ⇒ Summer University, Graz in space 2006 – Sep. 7-8, 2006, Graz nCME ¾ Solar phenomena : ● Parameters of CMEs: Coronal Mass Ejections size - angular width ΔCME increases in the beginning (< 5 RSun ) of propagation - Annual average widths of CMEs range from 45° (solar minimum) to 61° (close before activity maximum) ● Parameters of CMEs: density white light (Vourlidas, A., et al., ESA SP-506, 1, 91, 2002), radio (Gopalswamy & Kundu, Solar Phys., 143, 327, 1993), UV (Ciaravella, A., et al., ApJ., 597, 1118, 2003) ⇒ similar values at (3 - 5) RSun: nCME ~10 6 cm –3 Summer University, Graz in space 2006 – Sep. 7-8, 2006, Graz ¾ Solar phenomena : ● Parameters of CMEs: Coronal Mass Ejections latitude distribution ± Θ - Θ depends on distribution of closed magnetic field regions (active regions) on the solar surface. Average Θ = 60° (near the equatorial plane) - In the maximum of solar activity cycle, Θ spread up to all latitudes (± 90°) ● Parameters of CMEs: occurrence rate fCME correlates with Sunspot number ( SSN ), but differences in details: fCME peaks with a delay (~ 2 years) after the peak in the SSN Summer University, Graz in space 2006 – Sep. 7-8, 2006, Graz ¾ Solar phenomena : ● Parameters of CMEs: Coronal Mass Ejections latitude distribution ± Θ - Θ depends on distribution of closed magnetic field regions (active regions) on the solar surface. Average Θ = 60° (near the equatorial plane) - In the maximum of solar activity cycle, Θ spread up to all latitudes (± 90°) ● Parameters of CMEs: occurrence rate fCME correlates with Sunspot number ( SSN ), but differences in details: fCME peaks with a delay (~ 2 years) after the peak in the SSN Sunspot activity is confined to the active regions belt, but the CME activity occurs during the maxima at all latitudes Summer University, Graz in space 2006 – Sep. 7-8, 2006, Graz ¾ Solar phenomena : Coronal Mass Ejections ● Numeric simulation of CME eruptions (2.5D AMR-MHD numerical code) (S. Antiochos, J. Klimchuk, MacNeice, Naval Research Laboratory, USA) ♦ Key features of the model: - multipolar topology of mag. filed ( >2 flux systems with a null point above the erupting arcade); - strong photospheric shear near the central arcade neutral line - magnetic reconnection above the central arcade decreases the stabilizing effect of unsheared flux and allows the low-lying sheared flux to erupt. Summer University, Graz in space 2006 – Sep. 7-8, 2006, Graz ¾ Solar activity : Solar cycle ● Varying level of solar activity is closely related to the number of sunspots - 1843: Discovery of cyclic, ~ 11 year, variation in sunspot counts, i.e. in topology & strength of the global solar magnetic field (S. H. Schwabe, Germany) – the “Sunspot Cycle” - The 11 year sunspot cycle is related to 22 year cycle for reversal of the Sun's magnetic field Sunspot number variation (11-year cycle) Change of sunspot number and of solar UV Summer University, Graz in space 2006 – Sep. 7-8, 2006, Graz ¾ Solar activity : Solar cycle ● Monitoring of solar cycle ♦ Wolf number – method of sunspots counting (1848, J. R. Wolf, Switzerland): R = K ( 10 g +f ) K – observer’s personal features (~ 0.6) f – number of sunspots g – number of sunspot groups ♦ Variations of solar cycle in the past: Maunder Minimum (1645 – 1715) - corresponds to a “Little Ice Age” in Europe - Almost no sunspots on the Sun ♦ 11 years – the approximate value - 1750–1958: average period between max 10.9 yrs (7.3 - 17.1yrs) between min 11.1 yrs (9.0 - 13.6 yrs) Summer University, Graz in space 2006 – Sep. 7-8, 2006, Graz ¾ Solar activity : Solar cycle ● Butterfly diagram – first constructed in 1904 by E.W. Maunder ♦ Location of sunspots (latitudes) varies throughout the sunspot cycle: - solar min: around of 30° to 45° North & South - solar max: around of 15° North & South - end of a cycle (approaching the solar min): around 7° North & South Latitude migration of sunspot sites during the solar cycle forms butterfly pattern Summer University, Graz in space 2006 – Sep. 7-8, 2006, Graz ¾ The Sun : Open questions ● The most critical questions of the solar physics deal with the problems of the solar interior as well as with its outer atmosphere and heliosphere: ♦ How are the magnetic fields, observed at the solar surface, generated by dynamo processes and how are they destroyed ? The nature of Solar Cycle? ♦ What role do magnetic fields play in the organization of plasma structures and impulsive release of energy during the solar flares ? ♦ What are the mechanisms for heating of the solar corona and acceleration of the solar wind ? ♦ What magnetic configurations and evolutionary paths lead to formation of solar prominences and CMEs? ♦ What are the influences of the Sun on the Earth’s climate and on the near-Earth space weather ? Summer University, Graz in space 2006 – Sep. 7-8, 2006, Graz ¾ The Sun : Open questions Theoretical analysis and numeric modelling of the fundamental physical processes underlying the dynamic phenomena on the Sun should be combined with observations providing a resolution sufficient to observe scales characteristic to these processes. Summer University, Graz in space 2006 – Sep. 7-8, 2006, Graz ¾ Final Remark ● Herzsprung-Russell (H-R) diagram: the life cycle of the Sun (Change of the temperature and the luminosity) A: The Sun starts nuclear fusion in its core. `Birth' of the Sun. Summer University, Graz in space 2006 – Sep. 7-8, 2006, Graz ¾ Final Remark ● Herzsprung-Russell (H-R) diagram: the life cycle of the Sun (Change of the temperature and the luminosity) B: About half of the hydrogen supply in the core has been used up. The present time situation. Summer University, Graz in space 2006 – Sep. 7-8, 2006, Graz ¾ Final Remark ● Herzsprung-Russell (H-R) diagram: the life cycle of the Sun (Change of the temperature and the luminosity) C: There is no more hydrogen in the core. Fusion of hydrogen in the shell around the core starts. Radius: R → 1.4 x R Luminosity: L → 2 x L Summer University, Graz in space 2006 – Sep. 7-8, 2006, Graz ¾ Final Remark ● Herzsprung-Russell (H-R) diagram: the life cycle of the Sun (Change of the temperature and the luminosity) D: About 5 billion years from now: R → 3.3 x R and T ~ 4300 K. The temperature on Earth will â by ~ 100 degrees. The seas will be evaporated and present life will be destroyed. Within another 250 million years: R → 100 x R and L → 500 x L → Red Giant Summer University, Graz in space 2006 – Sep. 7-8, 2006, Graz ¾ Final Remark ● Herzsprung-Russell (H-R) diagram: the life cycle of the Sun (Change of the temperature and the luminosity) E: The core temperature of the Sun will rise so high that in one bang, all the rest of the He will fuse into carbon. By this explosion 1/3 of the solar envelope will be thrown out into space. Summer University, Graz in space 2006 – Sep. 7-8, 2006, Graz ¾ Final Remark ● Herzsprung-Russell (H-R) diagram: the life cycle of the Sun (Change of the temperature and the luminosity) The Sun will become brighter and the outer layers will be blown out into space in the form of a very dense solar wind → planetary nebula. Summer University, Graz in space 2006 – Sep. 7-8, 2006, Graz ¾ Final Remark ● Herzsprung-Russell (H-R) diagram: the life cycle of the Sun (Change of the temperature and the luminosity) Then, only a white dwarf remains, with a mass of about half of the mass of the current sun, but with a density of 2 tons per cm^3. This white dwarf will slowly cool down. The end of the solar system: Black dwarf Summer University, Graz in space 2006 – Sep. 7-8, 2006, Graz ¾ Final Remark ● Herzsprung-Russell (H-R) diagram: the life cycle of the Sun (Change of the temperature and the luminosity) So is the final… But we still have some time to learn more about our star the Sun ☺ Welcome on board !!! Summer University, Graz in space 2006 – Sep. 7-8, 2006, Graz ¾ Credits ● SOHO – Solar and Heliospheric Observatory: MDI - Michelson Doppler Imager; EIT - Extreme ultraviolet Imaging Telescope; SUMER - Solar Ultraviolet Measurements of Emitted Radiation; UVCS - Ultraviolet Coronagraph Spectrometer; CDS - Coronal Diagnostic Spectrometer LASCO - Large Angle Spectroscopic Coronagraph ● TRACE – Transition Region and Coronal Explorer ● NASA/Goddard Space Flight Center, Scientific Visualization Studio ● High Altitude Observatory which is a division of the National Center for Atmospheric Research, sponsored by the National Science Foundation ● Solar Theory section of Naval Research Laboratory, USA ● Windows to the Universe (http://www.windows.ucar.edu/) at the University Corporation for Atmospheric Research (UCAR) ● Jörg Weingrill – technical support and help in material preparation Summer University, Graz in space 2006 – Sep. 7-8, 2006, Graz