interior of the sun

Question 1

how to figure out lifetime of the sun

Answer 1

internal heat/ luminosity

Question 2

The Age Crisis: Part I

Answer 2

people thought the sun was powered by chemical or gravitational power.
Geologists estimated that the
Earth was at least a few Million
years old
so atp the sun would be younger than the earth

Question 3

Kelvin-Helmholtz mechanism: gravitational contraction

Answer 3

Gravity and Pressure in equilibrium

Question 4

Luminosity radiates away

Answer 4

heat… presure drops

Question 5

Balance tips in favor of gravity,

Answer 5

sun shrinks

Question 6

As Sun contracts

Answer 6

gas falls inward
* atoms
* gain speed
* are more
likely to
collide with
other atoms
Temperature
increases

Question 7

the sun contracting makes

Answer 7

Contraction makes interior heat up,
increasing the internal pressure
Balance restored, but with higher gravity,
pressure & temperature than before.

Question 8

The Sun could shine by tapping gravitational energy for

Answer 8

30 million years

Question 9

Today the Sun is in

Answer 9

hydrostatic equilibrium

Question 10

hydrostatic equilibrium in sun

Answer 10

Gas pressure due to an interior heat source
counteracts the inward pull of gravity

Question 11

Gas pressure due to an interior heat source
counteracts the inward pull of gravity

Answer 11

Early 20th century: radiometric
dating shows Earth is at least a
billion years old.
again how is the earth older than the sun.REthinking happened again

Question 12

fusion

Answer 12

lighter nuclei
combine to form heavier
nuclei

Question 13

fission

Answer 13

heavier nuclei split
to form lighter nuclei

Question 14

The Sun is powered by

Answer 14

by fusion
* Fuse 1 gram of H into 0.993
grams of He.
* Leftover 0.007 grams is
converted into energy: E = mc2
* Sun converts 600 million tons
of H every second!

Question 15

Only the Sun’s core is hot enough for fusion to occur

Answer 15

Four protons colliding
at once is unlikely.
* Must be hot:
>10 Million K to get
protons close enough
to fuse together

Question 16

The energy emitted by the Sun is produced

Answer 16

in a very small region at the very center of the Sun

Question 17

The chemical composition of the Sun 3 billion years ago was
different from what it is today in that it had

Answer 17

more hydrogen

Question 18

the proton-proton chain

Answer 18

Fuse 4 protons (1H) into one 4He nucleus plus:
* Energy in the form of Gamma-ray photons
* 2 positrons (positive electrons)
* 2 neutrinos that leave the Sun

Question 19

Neutrinos

Answer 19

neutral subatomic particles:
* Nearly massless, travel near c
* Interact weakly with matter
* Can pass through lead 1 parsec thick!
Neutrinos created in the Sun’s core should stream out of the Sun

Question 20

Energy is generated

Answer 20

in the core

Question 21

Energy is then
transported by

Answer 21

photons in the
Radiation Zone

Question 22

Energy is next
transported by

Answer 22

mass motions in the
Convection Zone

Question 23

Solar Oscillations

Answer 23

The Bottom Line
Fuse 4 protons (1H) into one 4He nucleus plus:
* Energy in the form of Gamma-ray photons
* 2 positrons (positive electrons)
* 2 neutrinos that leave the Sun
Fusion Lifetime is ~10 Billion Years
Neutrinos
Neutral subatomic particles:
* Nearly massless, travel near c
* Interact weakly with matter
* Can pass through lead 1 parsec thick!
Neutrinos created in the Sun’s core should stream out of the Sun.
Test: Solar Neutrinos
How do we know that fusion is
occurring in the core of the Sun?
Answer:
* Look for the neutrinos created by
the fusion reactions.
* Neutrinos from nuclear fusion,
with the expected energies,
detected in all experiments
performed to date.
The Solar Interior
1. Energy is generated
in the core.
2. Energy is then
transported by
photons in the
Radiation Zone.
3. Energy is next
transported by
mass motions in the
Convection Zone.
Solar Oscillations
* Doppler measurements
of gas pushed by sound
waves reaching the
surface
* few hundred m/s
* reveal what’s happening
in the Sun’s interior
* helioseismology

Question 24

Radiative zone

Answer 24

Density drops from ~20
g/cm3 (like gold) at the
base to 0.2 g/cm3 (less
than water) at the top
* Temperature drops to
2x106 K

Question 25

convection occurs in

Answer 25

outer 30% of the Sun Below 2x106 K, heavier
atoms (C, N, O, etc.)
hold onto more of their
electrons
* Harder for photons to
get through, heating up
gas
* Gas rises to the
photosphere

Question 26

The Sun is stable as a star because

Answer 26

gravity balances forces from pressure

Question 27

39
The primary source of energy in the Sun i

Answer 27

Fusion of light nuclei (H) to make heavier ones (He)