physics 55 friday, october 28, 2005 1.the sun as a star. 2.structure of the sun. 3.nuclear reactions...

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Physics 55 Friday, October 28, 2005 1. The Sun as a star. 2. Structure of the Sun. 3. Nuclear reactions that power the Sun. 4. How do we know what we know?

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Page 1: Physics 55 Friday, October 28, 2005 1.The Sun as a star. 2.Structure of the Sun. 3.Nuclear reactions that power the Sun. 4.How do we know what we know?

Physics 55Friday, October 28, 2005

1. The Sun as a star.2. Structure of the Sun.3. Nuclear reactions that power the Sun.4. How do we know what we know?

http://sohowww.nascom.nasa.gov/data/realtime/mpeg

Page 2: Physics 55 Friday, October 28, 2005 1.The Sun as a star. 2.Structure of the Sun. 3.Nuclear reactions that power the Sun. 4.How do we know what we know?

Talk by Dr. Jocelyn Bell Burnell TonightUNC 7pm Morehead Planetarium

Jocelyn Bell in 1968

Page 3: Physics 55 Friday, October 28, 2005 1.The Sun as a star. 2.Structure of the Sun. 3.Nuclear reactions that power the Sun. 4.How do we know what we know?

Mars, the Pleiades, Taurus, the Hyades

WARNING: Do not confuse the star Aldebaran in Taurus with Alderaan, the home planet of Princess Leia in the Star Wars movies!

Page 4: Physics 55 Friday, October 28, 2005 1.The Sun as a star. 2.Structure of the Sun. 3.Nuclear reactions that power the Sun. 4.How do we know what we know?

Mars Won’t Be This Close for 13 Years

Page 5: Physics 55 Friday, October 28, 2005 1.The Sun as a star. 2.Structure of the Sun. 3.Nuclear reactions that power the Sun. 4.How do we know what we know?

Our Sun as a Star: Chapter 15

Why does it shine?What is its structure?

How are the elements produced?How does the Sun affect Earth?

How do we know what we know?

http://sohowww.nascom.nasa.gov/data/realtime/mpeg

Page 6: Physics 55 Friday, October 28, 2005 1.The Sun as a star. 2.Structure of the Sun. 3.Nuclear reactions that power the Sun. 4.How do we know what we know?

Particular Properties of the Sun

Note: Total human energy consumption about 1011 watts

Page 7: Physics 55 Friday, October 28, 2005 1.The Sun as a star. 2.Structure of the Sun. 3.Nuclear reactions that power the Sun. 4.How do we know what we know?

Structure of the Sun

15,000,000 K

6000K

10,000 K

1,000,000 K

Who remembers role of solar wind in formation of solar system?

Page 8: Physics 55 Friday, October 28, 2005 1.The Sun as a star. 2.Structure of the Sun. 3.Nuclear reactions that power the Sun. 4.How do we know what we know?

Other Stars Have Similar Structures

Page 9: Physics 55 Friday, October 28, 2005 1.The Sun as a star. 2.Structure of the Sun. 3.Nuclear reactions that power the Sun. 4.How do we know what we know?

What Determines the Size of the Sun?Gravitational Equilibrium

Balance of gravitational forcetoward center and pressure outward (from thermal motion):“gravitational equilibrium”“hydrostatic equilibrium”

column,

2

or

versus

r r

PV NkT

P nkT

m MG

d

Page 10: Physics 55 Friday, October 28, 2005 1.The Sun as a star. 2.Structure of the Sun. 3.Nuclear reactions that power the Sun. 4.How do we know what we know?

Attempts to Estimate Lifetime of Sun in 1800s Led to a Mystery: Too Short!

“Calculating the age of the Earth and Sun” by Arthur Stinner,

Physics Education 37(4) 296-305 (2002).

30 7

26

2 10 kg of coal 3 10 J/(kg coal) 5,000 y

4 10 J/s

Helmholtz: Assume Sun with mass 1030 kg is made of combusting coal:30 7

26

2 10 kg coal 3 10 J/(kg coal) 5,000 y

4 10 J/s

Kelvin’s meteoric theory: energy of Sun supplied by meteors steadily falling into Sun, releasing gravitational potential energy. Anyone see a way to test this idea?

Kelvin and Helmholtz: Assume energy released by conversion of gravitational potential energy into kinetic energy of mass falling inward toward center: ~ 60,000,000 years with Sun shrinking only about 80 m in radius per year.

All known mechanisms fail to give age consistent with geology and biology of billions of years, what is going on?

Page 11: Physics 55 Friday, October 28, 2005 1.The Sun as a star. 2.Structure of the Sun. 3.Nuclear reactions that power the Sun. 4.How do we know what we know?

Radioactivity

Page 12: Physics 55 Friday, October 28, 2005 1.The Sun as a star. 2.Structure of the Sun. 3.Nuclear reactions that power the Sun. 4.How do we know what we know?

Nuclear Reactions

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