Answer to Question 1
Astronomers can measure magnetic fields on the Sun using the Zeeman effect. When an atom is in a magnetic field, the electron energy levels are altered, and the atom is able to absorb photons with a greater variety of wavelengths than the same atom not in a magnetic field.
Answer to Question 2
The Babcock model explains the reversal of the Sun's magnetic field from cycle to cycle. As the magnetic field becomes tangled, adjacent regions of the Sun's surface are dominated by magnetic fields that point in different directions. After about 11 years of tangling, the field becomes so complex that adjacent regions of the surface are forced to change their magnetic field directions to align with neighboring regions. The entire field quickly rearranges itself into a simpler pattern, and differential rotation begins winding it up to start a new cycle. The newly organized field is reversed, and the next sunspot cycle begins with magnetic north replaced by magnetic south. Consequently, the complete magnetic cycle is 22 years long, whereas the sunspot cycle is 11 years long.
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