1. The Sun
Part 2

2. How do we know what is going on inside the Sun?
Mathematical Models
Mathematical models provide predictions that can be compared to observed data.
The good agreement we get reassures us that our models are reasonable.

3. How do we know what is going on inside the Sun?
Mathematical Models
Solar vibrations (helioseismology)
Just as we use seismic waves in the Earth to learn about what we can’t see inside the Earth,
we can use waves traveling through the Sun to tell us about the solar interior.
Helioseismologists call this a Dopplergram

4. An image from today
Movies from SDO/HMI…

5. How do we know what is going on inside the Sun?
Mathematical Models
Solar vibrations (helioseismology)
Solar neutrinos
The Homestake Mine in South Dakota was the site of the first experiment to detect solar neutrinos
Unfortunately, it only detected one-third the number of neutrinos predicted
This was known as the
“solar neutrino problem”

6. How do we know what is going on inside the Sun?
Mathematical Models
Solar vibrations (helioseismology)
Solar neutrinos
A later version of the experiment, the Sudbury Neutrino Observatory in Canada, was able to detect all three types of neutrinos.
It detected the predicted number.
This did two things:
Confirmed our model of the nuclear reactions in the Sun
Answered an old question in particle physics: Do neutrinos have any mass at all?
(The answer is yes, they do!)

7. If we can't see the Sun's interior, how do we know what it is like?
observations of sunquakes
observations of neutrinos
our understanding of gravitational equilibrium
all of the above
B and C

8. Sunspots
Sunspots are places where the Sun’s magnetic field lines pop out of the Sun.
They loop back in at another sun spot.
We know this because of the Zeeman Effect.

9. Sunspots
The magnetic fields trap hot plasma, allowing it to cool without being replaced by hotter plasma.
The cooler gas appears darker to us: that’s black body radiation again!

10. Charged particles looping along these field lines radiate X-rays that can be detected by orbiting observatories.

11. Extremely large loops are called “solar prominences”.
UV image from Solar Dynamics Observatory

12. X-ray image from NASA’s Trace mission
When the loops get too tightly twisted, they can snap, releasing huge amounts of energy (X-rays) and charged particles. This is known as a “solar flare”.
X-ray image from NASA’s Trace mission

13. This is known as a “coronal mass ejection” (CME).
Sometimes flares and other solar storms eject tons of charged particles in large bubbles.
This is known as a “coronal mass ejection” (CME).
These cause the most damage to spacecraft in orbit and electronics systems on Earth, as well as posing the largest threat to astronauts in space.
X-ray image from NASA’s SOHO mission

14. Blackouts, auroras, and satellite damage are some of the ways solar activity can affect us on Earth.

15. The solar cycle Sunspot counts over time
Visible solar activity varies over an 11-year period.
Solar maximum was predicted to peak in 2013, but it’s been a very strange cycle…
“Butterfly diagram”

16. Sunspot counts during this cycle have been fairly low
Some predictions suggest the next maximum may be even lower

17. The cause of the solar cycle Differential rotation
The Sun rotates faster at the equator than it does near its poles (same as Jupiter).
This causes the magnetic field lines to twist tighter and tighter, storing huge amounts of potential energy.
It’s that energy that drives sunspots, solar flares and prominences, and CMEs.

18. The cause of the solar cycle Differential rotation
During solar maximum, something goes on inside the Sun causing the north and south magnetic poles to start swapping places. By the time solar max is over, north has become south and vice versa.
So the solar cycle is really 22 years long.

19. What does the “Butterfly diagram” tell us?
A) Times of high sunspot activity coincide with times of large butterfly populations.
B) At the beginning of a solar cycle, the sunspots mostly appear in mid-latitudes; later in the cycle they are found closer to the equator.
C) The solar cycle is really 22 years long.
D) Magnetic field lines popping out of the Sun look like butterfly wings.

20. The Sunspot Cycle and Earth’s Climate
The “Maunder Minimum” coincided (generally) with a cold period known as the “Little Ice Age”
A mechanism is not understood.
Of course, it could be coincidence.
The current trend of rising average temperatures can only be explained by human release of CO2.