ASTR100 (Spring 2008) Introduction to Astronomy Our Star Prof. D.C. Richardson Sections 0101-0106.
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Transcript of ASTR100 (Spring 2008) Introduction to Astronomy Our Star Prof. D.C. Richardson Sections 0101-0106.
Lifetime =
Total EnergyLuminosity
• This helps explain why the Sun shines!…
Luminosity
Luminosity is light energy emitted per unit time.
Measured in Watts (Joules per second).
Our Sun’s luminosity is 3.8 × 1026 W. That’s a lot of 100-W lightbulbs!!
Is it powered by NUCLEAR ENERGY?
Luminosity~ 10 billion yearsNuclear Potential Energy (core)
E = mc2
- Einstein, 1905
Is it powered by NUCLEAR ENERGY? … YES!
Luminosity~ 10 billion yearsNuclear Potential Energy (core)
E = mc2
- Einstein, 1905
The Sun is in gravitational equilibrium…
The outward push of pressure balances the inward pull of gravity.
Gravitational contraction…
Provided energy that heated core as Sun was forming.
Contraction stopped when fusion began.
Radius:
6.9 x 108 m
(109 times Earth)
Mass:
2 x 1030 kg
(300,000 Earths)
Luminosity:
3.8 x 1026 Watts
Fission
Big nucleus splits into smaller pieces.
(Nuclear power plants)
Fusion
Small nuclei stick together to make a bigger one.
(Sun, stars)
High temperature enables nuclear fusion to happen in the core.
(Atoms move faster when they’re hotter.)
The Sun releases energy by fusing four hydrogen nuclei into one helium nucleus in several steps.
The sequence of steps is called the proton-proton chain.
Thought Question
What would happen inside the Sun if a slight rise in core temperature led to a rapid rise in fusion energy?
A. The core would expand and heat up slightly.
B. The core would expand and cool.C. The Sun would blow up like a
hydrogen bomb.
Thought Question
What would happen inside the Sun if a slight rise in core temperature led to a rapid rise in fusion energy?
A. The core would expand and heat up slightly.
B. The core would expand and cool.C. The Sun would blow up like a
hydrogen bomb.Solar thermostat keeps burning rate steady
Solar Thermostat
Drop in core temperature causes fusion rate to drop, so core contracts and heats up.
Rise in core temperature causes fusion rate to rise, so core expands and cools down.
We learn about the inside of the Sun by…
Making mathematical models. Observing “sunquakes”. Observing solar neutrinos.
Patterns of vibration on the surface tell us what the Sun is like inside.
Results agree very well with mathematical models of the solar interior.
Neutrinos created during fusion fly directly through the Sun.
Observations of these solar neutrinos can tell us what’s happening in core.
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.
Solar activity is like “weather”…
Sunspots. Solar prominences. Solar flares. Coronal mass ejections.
All are related to magnetic fields.
Sunspots
Cooler than other parts of the Sun’s surface (4000 K).
Regions with strong magnetic fields.Click me!
Magnetic activity causes solar flares that send bursts of X-rays and charged particles into space.
Click me!
Coronal mass ejections send bursts of energetic charged particles out through the solar system.
Click me!
Charged particles streaming from Sun can disrupt electrical power grids and disable communications satellites.