Information about Midterm #1 Grades are posted on course website Average = 129/180, s.d. = 27...
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Transcript of Information about Midterm #1 Grades are posted on course website Average = 129/180, s.d. = 27...
Information about Midterm #1
• Grades are posted on course website
• Average = 129/180, s.d. = 27
• Highest 180/180
• Scores below 100 => “serious concerns”
• Next midterm: Tuesday, November 15 (sec 3) or Wednesday, November 16 (sec 4)
• Pick up exams in labs, and keep for studying for midterm #2
It is powered by NUCLEAR ENERGY!
Luminosity~ 10 billion years
Nuclear Potential Energy (core)
E = mc2
—Einstein, 1905
Gravitational contraction…
provided energy that heated the core as the Sun was forming.
Contraction stopped when fusion began replacing the energy radiated into space.
Fission
Big nucleus splits into smaller pieces
(Nuclear power plants)
Fusion
Small nuclei stick together to make a bigger one
(Sun, stars)
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
Decline 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
Structure of the Sun
We learn about the inside of the Sun by …
• making mathematical models.
• observing solar vibrations.
• observing solar neutrinos.
Neutrinos created during fusion fly directly through the Sun.
Observations of these solar neutrinos can tell us what’s happening in the core.
Solar neutrino problem:
Early searches for solar neutrinos failed to find the predicted number.
(Note: Ray Davis was awarded the 2002 Nobel Prize in Physics for making this observation)
Solar neutrino problem:
Early searches for solar neutrinos failed to find the predicted number
More recent observations also found a deficit of neutrinos.
A new theory of the neutrino predicts that they have mass and can change form. This theory agrees with the observed neutrino numbers.
Solar activity is like “weather”
• Sunspots
• Solar flares
• Solar prominences
All are related to magnetic fields.
Sunspots…
Are cooler than other parts of the Sun’s surface (4,000 K)
Are regions with strong magnetic fields
Zeeman Effect
We can measure magnetic fields in sunspots by observing the splitting of spectral lines
Charged particles streaming from the Sun can disrupt electrical power grids and disable communications satellites.