© 2010 Pearson Education, Inc. The Sun

© 2010 Pearson Education, Inc. Why was the Sun’s energy source a major mystery?

© 2010 Pearson Education, Inc. Is it on FIRE?

© 2010 Pearson Education, Inc. Is it on FIRE? Luminosity ~ 10,000 years Chemical energy content

© 2010 Pearson Education, Inc. Is it on FIRE? … NO! Luminosity ~ 10,000 years Chemical energy content

© 2010 Pearson Education, Inc. Is it CONTRACTING? Insert TCP 6e Chapter 14 opener

© 2010 Pearson Education, Inc. Is it CONTRACTING? Luminosity Gravitational potential energy ~ 25 million years

© 2010 Pearson Education, Inc. Is it CONTRACTING? … NO! Luminosity ~ 10,000 years Chemical energy content

© 2010 Pearson Education, Inc. Why does the Sun shine?

© 2010 Pearson Education, Inc. It can be powered by NUCLEAR ENERGY! (E = mc 2 ) Luminosity ~ 10 billion years Nuclear potential energy (core)

© 2010 Pearson Education, Inc. Weight of upper layers compresses lower layers. Insert TCP 6e Figure 14.1

© 2010 Pearson Education, Inc. Gravitational equilibrium: Energy supplied by fusion maintains the pressure that balances the inward crush of gravity.

© 2010 Pearson Education, Inc. Gravitational contraction: Provided the energy that heated the core as Sun was forming Contraction stopped when fusion began.

© 2010 Pearson Education, Inc. Radius: 6.9  10 8 m (109 times Earth) Mass: 2  kg (300,000 Earths) Luminosity: 3.8  watts

© 2010 Pearson Education, Inc. What is the Sun’s structure? Insert TCP 6e Figure 14.3

© 2010 Pearson Education, Inc. Solar wind: A flow of charged particles from the surface of the Sun

© 2010 Pearson Education, Inc. Corona: Outermost layer of solar atmosphere ~1 million K

© 2010 Pearson Education, Inc. Chromosphere: Middle layer of solar atmosphere ~ 10 4 –10 5 K

© 2010 Pearson Education, Inc. Photosphere: Visible surface of Sun ~ 6000 K

© 2010 Pearson Education, Inc. Convection Zone: Energy transported upward by rising hot gas

© 2010 Pearson Education, Inc. Radiation Zone: Energy transported upward by photons

© 2010 Pearson Education, Inc. Core: Energy generated by nuclear fusion ~ 15 million K

© 2010 Pearson Education, Inc. How does nuclear fusion occur in the Sun?

© 2010 Pearson Education, Inc. Fission Big nucleus splits into smaller pieces. (Example: nuclear power plants) Fusion Small nuclei stick together to make a bigger one. (Example: the Sun, stars)

© 2010 Pearson Education, Inc. High temperatures enable nuclear fusion to happen in the core.

© 2010 Pearson Education, Inc. The Sun releases energy by fusing four hydrogen nuclei into one helium nucleus.

© 2010 Pearson Education, Inc. The proton–proton chain is how hydrogen fuses into helium in Sun.

© 2010 Pearson Education, Inc. IN 4 protons OUT 4 He nucleus 2 gamma rays 2 positrons 2 neutrinos Total mass is 0.7% lower.

© 2010 Pearson Education, Inc. Convection (rising hot gas) takes energy to surface.

© 2010 Pearson Education, Inc. Bright blobs on photosphere show where hot gas is reaching the surface.

© 2010 Pearson Education, Inc. Neutrinos created during fusion fly directly through the Sun. Observations of these solar neutrinos can tell us what’s happening in core.

© 2010 Pearson Education, Inc. Solar neutrino problem: Early searches for solar neutrinos failed to find the predicted number. More recent observations find the right number of neutrinos, but some have changed form.

© 2010 Pearson Education, Inc. What causes solar activity?

© 2010 Pearson Education, Inc. Solar activity is like “weather”. Sunspots Solar flares Solar prominences All these phenomena are related to magnetic fields.

© 2010 Pearson Education, Inc. Sunspots Are cooler than other parts of the Sun’s surface (4000 K) Are regions with strong magnetic fields

© 2010 Pearson Education, Inc. Zeeman Effect We can measure magnetic fields in sunspots by observing the splitting of spectral lines.

© 2010 Pearson Education, Inc. Loops of bright gas often connect sunspot pairs.

© 2010 Pearson Education, Inc. Magnetic activity causes solar flares that send bursts of X rays and charged particles into space.

© 2010 Pearson Education, Inc. Magnetic activity also causes solar prominences that erupt high above the Sun’s surface.

© 2010 Pearson Education, Inc. Charged particles streaming from the Sun can disrupt electrical power grids and can disable communications satellites.

© 2010 Pearson Education, Inc. How does solar activity vary with time?

© 2010 Pearson Education, Inc. The number of sunspots rises and falls in an 11-year cycle. Insert TCP 6e Figure 14.21a unannotated Insert TCP 6e Figure 14.21b unannotated

© 2010 Pearson Education, Inc. The sunspot cycle has something to do with winding and twisting of the Sun’s magnetic field.