(1) Suppose a sunspot has a surface temperature that is 1,800 K cooler than the surrounding

photosphere (whose T = 5800 K). Per unit area, what is the amount of light emitted each second by

the sunspot relative to the photosphere?

2. (3 points.) Why should we on Earth be concerned about solar flares and coronal mass ejections?

3. (3 points.) What do we think is the source of most of the energy that goes into heating the solar chromosphere and corona, making them hotter than the Sun's photosphere?

4. (3 points.) If the Sun's rotation period is about 4 weeks, roughly how long would it take a sunspot to appear to move from the edge (limb) of the Sun's disk to the center of the Sun's disk?

5.The Sun's surface temperature is about 5,800 K and its spectrum peaks at

5,000 A. An O-type star's surface temperature may be 45,000 K. (a) (2 points.) According to Wien's law, at what wavelength does its spectrum peak? (b) (1 point.) In what part of the spectrum might that peak be? (c) (2 points.) Can the peak be observed with the Keck telescopes on Maunakea in Hawaii? Explain. (Note that 5,000 = 500 mm. We have generally used nm in lecture, but the textbook uses : you can use either in your answer to part (a).)