The Sun. 1a. The Photosphere. A. The Solar Atmosphere. 1b. Limb Darkening. A. Solar Atmosphere. B. Phenomena (Sunspots) C.

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1 The Sun 1 The Sun A. Solar Atmosphere 2 B. Phenomena (Sunspots) Dr. Bill Pezzaglia C. Interior Updated 2006Oct31 A. The Solar Atmosphere 1. Photosphere 2. Chromosphere 3. Corona 4. Solar Wind 3 1a. The Photosphere Most of the light we see comes from the photosphere. It corresponds to a black body 4 1b. Limb Darkening Sun appears fainter near edge. Tells us about the change in temperature from bottom to top of photosphere. 5 1c. Temperature plot distinguishes parts of solar atmosphere 6 1

2 1d. Fraunhofer Lines The Fraunhofer lines in the solar spectra tells us the composition of the sun Fraunhofer lines come from absorption in the cooler upper photosphere (lower chromosphere). 7 8 Composition of Sun 9 2a. The Chromosphere About 1000x fainter than photosphere See it using H-alpha filter 10 2b. Spicules Small, jet-like eruptions seen throughout the chromospheric network. They appear as short dark streaks in the H-alpha image to the. They last but a few minutes but in the process eject material off of the surface and outward into the hot corona at speeds of 20 to 30 km/s. 11 2c. Filaments & Plage Filaments are dark, threadlike features seen in the red light of hydrogen (H-alpha). These are dense, somewhat cooler, clouds of material that are suspended above the solar surface by loops of magnetic field. Plage, the French word for beach, are bright patches surrounding sunspots that are best seen in H-alpha. Plage are also associated with concentrations of magnetic fields and form a part of the network of bright emissions that characterize the chromosphere. 12 2

3 2d. Prominences 13 2e. The Transition Region 14 Prominences are dense clouds of material suspended above the surface of the Sun by loops of magnetic field. Prominences and filaments are actually the same things except that prominences are seen projecting out above the limb, or edge, of the Sun. Both filaments and prominences can remain in a quiet or quiescent state for days or weeks. However, as the magnetic loops that support them slowly change, filaments and prominences can erupt and rise off of the Sun over the course of a few minutes or hours Viewed with Carbon IV emission line Temperature of about 100,000ºC The transition region is a thin and very irregular layer of the Sun's atmosphere that separates the hot corona from the much cooler chromosphere. Heat flows down from the corona into the chromosphere and in the process produces this thin region where the temperature changes rapidly from 1,000,000ºC (1,800,000ºF) down to about 20,000ºC (40,000ºF). Hydrogen is ionized (stripped of its electron) at these temperatures and is therefore difficult to see. Instead of hydrogen, the light emitted by the transition region is dominated by such ions as C IV, O IV, and Si IV (carbon, oxygen, and silicon each with three electrons stripped off). These ions emit light in the ultraviolet region of the solar spectrum that is only accessible from space. 3a. The Corona 15 3b. The Coronagraph 16 A million times fainter than photosphere, and its fainter than blue sky. Hence can only see it during solar eclipses Or you fake a solar eclipse using a coronagraph, invented 1930 by the French astronomer Bernard Lyot 3c. Corona Mass Ejection 17 3d. Corona from Space 18 CME: An explosion that takes place in the corona that ejects particles into the solar wind, caused by an energy release in the Sun's magnetic field From UV and X-Ray telescopes out in space we can now see the full corona using various spectral lines. 3

4 3e. Corona Holes Holes in the Corona are often associated with massive ejections and flares. 19 4a. The Solar Wind Made of charged particles (protons and electrons), hits the earth s magnetic field and reshape it. 20 4b. Auroras When bursts of solar wind hit the earth s magnetic field, we get auroras. 21 4c. More Auroras 22 4d. More Auroras 23 B. Surface Phenomena Sunspots 2. Sunspot Cycle 3. Flares, etc 4

5 1a. Sunspots 25 1b. Sunspots 26 Umbra is dark spot in center, cooler at 4000K Penumbra is around it, with filaments They last several weeks. 1c. Sunspots Solar Rotation 28 Galileo uses sunspots to determine the sun is rotating. 2b. Differential Rotation Sun doesn t spin as a single ball Differential rotation messes up magnetic field of sun 29 3a. Magnetic Fields Zeeman effect: splitting of spectral lines due to magnetic fields, shows us sunspots have BIG magnetic fields 30 5

6 3b. Magnetographs 31 You can map the sun s magnetic field using Zeeman effect and see the sunspots correlate to it. 3c. Sunspots Theory Theory is magnetic fields mess up convection, so makes a local cool spot. 32 3d. Sunspot Pairs 33 Sunspots come in pairs of opposite magnetic poles, in east-west direction 3e. Sunspots and flares The flares follow the magnetic field lines. 34 3f. Sunspot and flares 35 4a. Sunspot Cycle year cycle of sunspot activity During minima there are often no sunspots at all Correlated to flipping of sun s magnetic poles. 6

7 4b. Butterfly Diagram 1904 Maunder showed that sunspots tend to be in higher latitudes at beginning of solar cycle, but closer to equator during solar maximum. 37 4c. Sunspot Cycle Sunspot cycle stopped for (Maunder Minimum). The earth got slightly colder then. 38 4d. Father Ricard, Santa Clara U. Had a theory that sunspots were correlated with weather, but he was not taken too seriously 39 4e. Sun is warmer with sunspots Recent study has shown it may be true! The sun is hotter when there are sunspots. 40 4f. Sunspot activity and Earth s Climate 41 C. The Interior 1. Energy Production in Core The Radiation Zone 3. The Convection Zone 7

8 43 1. Helioseismography 44 How do we KNOW anything about the inside of the sun? Measure vibrations on the surface of the sun (doppler effect) Can tell us about the inside Find that Radiation Zone rotates as a single ball Convection zone size is bigger than previously thought Can t tell much about the core this way. Can tell if there are sunspots on the back side of the sun! 1b. Energy is produced in core Only in center is pressure and temperature hot enough to fuse hydrogen into helium. Mass is lost, converted into energy Einstein s formula: E=mc 2 E=Energy M=mass c= speed of light 45 1c. Proton Proton Chain Hydrogen burning at the center of the Sun usually takes place in a three-step process. Step 1: Two protons (hydrogen nuclei, shown in red) combine to form a deuterium (proton+neutron), plus a massless neutrino and positron (anti electron). The positron annihilates an electron producing gamma rays (photons). Step 2: The deuteron combines with a third proton, forming an isotope of helium (3He) and releasing another gamma-ray photon. 46 Step 3: Two 3He nuclei formed via the first and second steps collide, forming a different helium isotope with two protons and two neutrons (4He) and releasing two protons. The gamma-ray photons released in these steps, as well as the kinetic energy (energy of motion) of the released protons, are the source of the Sun's energy. 2a. The Radiation Zone 47 2b. The Radiation Zone 48 It is so dense inside, that it takes light over a million years to get from core to the surface through the radiation zone But neutrinos from the core will escape and arrive in earth in 8 minutes. 8

9 2c. The Neutrino Experiment 49 3a. The Convection Zone 50 Measurements of neutrinos on the earth would tell us what is happening in the core right now! First results: ZERO Is the sun off? About to go dark? 2 nd Results: nonzero but lower than expected. Scientists are CONFUSED! Heat goes through the last layer of the sun fairly fast. 3b. Granulation You see the tops of the convection cells on the sun as granulation 3c. Granulation What about supergranules? Notes/References