1 Chapter 8: The Sun The Sun is the nearest star to Earth, and provides the energy that makes life possible. PRIMARY SOURCE OF INFORMATION about the nature of the Universe NEVER look at the Sun directly!! Must understand its power!! Must understand proper ways to view it!!
2 TEMPERATURE (T) = average kinetic energy of atoms or molecules: Can also think as being the average speed, Vavg T is proportional to Vavg Speed of O2, N2 in the atmosphere at room temperature is about: 1,720 km/hr. Elementary Particles and Forces
3 Surveying the Sun-scape The Sun is a Star shining under its own power with energy from Nuclear FUSION. Nuclei combine to form more complex ones: The Sun also powers the rest of the Solar System, including Earth Produces HUGE amount of energy: 92 billion one-megaton nuclear bombs per second!!!! If made of COAL would burn up in 4,600 years!!!! Fossil evidence on Earth shows formed more than 3 billion years ago, probably 4.6 billion years!!!! Only nuclear fusion could produce so much energy!!!! E = MC 2 CENTER of the Sun HUGE pressure and a temperature of about 16 MILLION 0 C. Hydrogen is FUSED to helium About 700 million tons of hydrogen turn into helium EVERY SECOND near the center of the Sun, AND 5 million toms vanish and turn into PURE ENERGY
4 The Sun s size and shape: A great bundle of gas GRAVITY keeps the Sun held together. As gravity tends to shrink the size of the Sun, gravitational energy is changed in to kinetic (moving) energy of the Hydrogen, and Helium. Radiation/heat pressure pushes the other way!! BALANCE!! The Sun is 300,000 times the mass of Earth The diameter for balance is: 1,391,000 kilometers; huge gravity and pressure Rotates once every 25 days, so fairly round
5 PART 2: The Sun s regions: Caught between the core and the corona Energy Moving from Core to Photosphere (POWER POINT: COSMIC PERSPECTIVE) Sun has two (2) main regions: Inside and Outside ( ATMOSPHER ): Below the PHOTOSPHERE is the STELLAR INTERIOR (core + radiation zone + convection zone)
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7 The (right) illustration depicts two positive protons separated by a distance of r. Because the repulsive electric force is proportional to 1/r 2, at great separation distances it approaches zero. But as the charge gets close together it approaches infinity. But when the protons get as close as 10-15 meters apart, the tremendously large nuclear attractive force kicks in and fuses the protons together. At the CENTER is the CORE (v) (1.) p + p 2 H + e + (positron) + neutrino (2.) 2 H + p 3 He + gamma ray (y) (3.) 3 He + 3 He 4 He + p ( 1 H) + p ( 1 H) Note that steps 1 and 2 must be done twice for each step 3.
8 CORE: Fusion takes place, releasing light (gamma rays) and neutrinos While the gamma rays bounce off free electrons and protons they on average migrate upwards, but very randomly and gradually It takes HUNDREDS of THOUSANDS of years for energy to go from the core to the photosphere!!! The neutrinos have very little interaction, and zip straightly out of the Sun Moving upwards and outwards it becomes cooler, and less pressure The inner ENERGY GENERATING CORE extends 180,000 miles!! RADIATIVE ZONE: Photons move at speed of light while continuously scattering of other particles in a very random fashion, while very slowly moving outwards on average.
9 CONVECTION ZONE starts at about 494,000 miles from core center Like boiling water, heat and gas move upwards, is cooled, and falls back downwards. From bottom to top the temperature drops from 2.2 million to 5,500 0 C. Lots of turbulence while creating fluctuating magnetic fields.
MAGNETIC FIELDS 10 Magnet Fields A stationary charge, like an electron produces an Electric field (E) A moving electric charge produces a magnetic field (B) A moving charged particle spirals around magnetic field lines An accelerated charge produces electro-magnetic waves (LIGHT)
11 The rotation of the Sun is quite complex, since it is composed of ionized gas (atoms stripped down to positive nuclei (protons) and free electrons). At the equator this gas has a rotational speed of one cycle in about 25 Earth days. At the poles it is much slower, taking about 38 Earth days to make one revolution. Thus, the magnetic fields produced by the rotating charge become complicated and twisted, since it results from mixtures originating in various regions of the Sun. Further there is the rising and falling charge and great turbulence in the convective zone. The illustration above shows how the resulting magnetic fields become entangled and complex.
Atmosphere of the Sun 12 Photosphere, which is the origin of the light we see. We see it because there is a high intensity of light in the visible region Black SUNSPOTS are seen on the Photosphere where strong magnetic fields protrude CHROMOSPHERE (color sphere); 1,600 km thick; 10,000C; VERY TURBULENT; charged particles rushing along field lines and flying out of Sun From this region UV light is strong CORONA, extremely rarified and electrified; shape determined by the magnetic field; ONE MILLION 0 C: Thus lots of X-rays Energy is pumped into this region along magnetic field lines. But the density of atoms is very LOW. PRMONENCES: loops of magnetic field lines along which charged particles move
Solar activity: What s going on out there? 13 Various things: 11-year sunspot cycle; other longer ones that involve magnetism. Sun spots regions of intense magnetic fields Coronal mass ejections: The mother of solar flares People thought main ejections are solar flares, originating in the photosphere Now believe believed to be CORONAL MASS EJECTIONS, huge eruptions high in the chromospheres During the peak of the 11-year cycle, a pole reversal also takes place where north becomes south, and vise versa.
14 Can be more clearly seen during an eclipse of the Sun Cycles within cycles: The Sun ands its spots Sunspots are regions of the photosphere where the magnetic fields are strong. Usually 11 years between the peaks of the cycles Number of spots varies; reason unknown Move across the surface due to the Sun s rotation. The solar constant : Time to face the changes Total amount of energy produced by the Sun is solar luminosity The amount that reaches Earth is the solar constant But not really constant: less energy when the sunspots face Earth
15 Solar wind: Playing with magnets Solar wind (electrons and protons) is constantly streaming out from the CORONA Travels at a speed of about one million miles per hour This produces the aurora Solar CS1: The mystery of the missing solar neutrinos During fusion in the core and huge amount of NEUTRINOS are produced These have almost (???) no mass and travel at the speed of light and can pass through anything Detectors around the world counted fewer neutrinos than expected, which was a huge mystery This was solved when noticed that there are different varieties of neutrinos, and they can switch while in flight Before could not detect these, but now can, and numbers are good
16 Four billion and counting: The life expectancy of the Sun Sun has about 5 billion years more to live Will eventually become unstable, shrink, then expand to a red giant, and the explode the outer atmosphere OBSERVING (NO LECTURE; read this part of book by self)