Goals Describe the internal structure of the Sun Describe the surface detail and how it probes the interior Describe how the Sun’s magnetic field effects solar activity Explain the energy source of the Sun: Nuclear fusion Explain how understanding the Sun has helped define Physics

The Sun is our nearest star The Sun is our nearest star. The next closest star is 300,000 times further away (Alpha Centauri). Alpha Centauri is 4.3 light years away and our Sun is 8 light minutes away. Our Sun is absolutely average in every aspect (size,mass, brightness, etc.) compared to the other stars in our galaxy. The Sun is 300,000 times more massive than the Earth and its radius is more than 100 times the size of Earth’s.

The Sun is a mass of incandescent gas. It has no solid surface. The “surface”, called the photosphere is simply where the gas becomes optically thick and we can’t see through it. Since the surface becomes “thick” in just 0.1 percent of the radius, the Sun appears to have a sharp edge.

There are three well defined regions which are defined by the way energy is transported within them. In the core is the site of continuous nuclear reactions which convert mass into energy according to E=MC2 . (100 billion, 1-megaton nuclear bombs/sec). The radiation zone is where the Sun appears transparent to the energy and photons move freely. The convection zone is where hot material rises to the surface like a pot of boiling water.

The Sun is stable because of hydrostatic equilibrium

The Sun, being made up of gasses, wiggles, shakes, and rings like a giant bowel of Jell-O. The way in which it rings tells us about its interior just like seismic waves tell us about the interior of the Sun just like seismic waves tell us about the interior of the Earth. This field of study is called helioseismology

Scientists modeling the Sun calculate that the temperature at the core is near 15,000,000 K while we measure the black body radiation curve at the surface and get 5,800 K. As the convection cells near the surface and radiate their energy away, we see their effect as granulation.

The Solar Atmosphere A Spectrum of our Sun shows many dark absorption lines, indicating the presence, in the lower solar atmosphere, of 67 elements in various stages of ionization.

Solar Chromosphere Solar Surface Corona Holes in X-rays Solar Corona

Sun Spots Sunspots are actually cool spots on the Sun which look dark because they give off less light than the surroundings

Sunspots occur in pairs, one being a north pole the other being the south. They are produced when knots of magnetic fields surface from below caused by their wrapping due to differential rotation.

Because of the coupling between matter and magnetic fields, the differential rotation and convection twist the magnetic field lines.

It takes about 11 years for the magnetic field lines to get all wrapped around, and then the poles of the sun actually flip. What was north is now south. This causes the 11 year sunspot cycle.

Hot gasses which are boiling off the Sun tend to follow the magnetic field lines, producing loops, prominences, and flares. Those that escape make the Solar wind.

Energy from the Sun It wasn’t till early this century when Albert (Al) Einstein produced the Special Theory of Relativity that we understood how the Sun gets its energy. The famous equation E = MC2 shows how matter can be converted to energy (and vise versa)

The Sun (and all stars) through a process called the proton-proton cycle converts 4 H nuclei into He and giving up energy. This is the same process used in a Hydrogen bomb. A Hydrogen bomb is just a piece of the core of the Sun released on Earth for a brief amount of time.

The only major unknown concerning the energy production of the Sun is the amount of neutrinos (30-50% less) being produced. Several underground chambers have been built to detect neutrinos to help solve this problem.