Chapter 9 The Sun

Chapter 9 The Sun

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.

Chapter 9 The Sun

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.

Chapter 9 The Sun

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.

Chapter 9 The Sun

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

Chapter 9 The Sun

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.

Chapter 9 The Sun

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.

Chapter 9 The Sun

Solar Chromosphere

Solar Corona

Solar Surface

Corona Holes in X-rays

Chapter 9 The Sun

Sun Spots

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

Chapter 9 The Sun

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.

Chapter 9 The Sun

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.

Chapter 9 The Sun

Hot gasses which are boiling off the Sun tend to follow the magnetic field lines, producing loops, prominences, and flares.

Chapter 9 The Sun

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)

Chapter 9 The Sun

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.

Chapter 9 The Sun

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.

Chapter 9 The Sun

Sun grazing comets 1Sun grazing comets 2Sun blows off comet tailDifferential rotation animationSolar rotationSolar eruption