The Solar System

PART 2 | THE STARS

Learning to Look

1. Whenever there is a total solar eclipse,
   you can see something like the image
   shown at right. Explain why the shape
   and extent of the glowing gases is differ-
   ent for each eclipse.


2. The two images at right show two solar
   phenomena. What are they, and how are
   they related? How do they differ?


3. This image of the sun was recorded in
   the extreme ultraviolet by the SOHO
   spacecraft. Explain the features you see.


4. What observations would you make if you were ordered to set up a
   system that could warn astronauts in orbit of dangerous solar fl ares?
   Such a warning system exists.

Problems

1. The radius of the sun is 0.7 million km. What percentage of the radius
   is taken up by the chromosphere?


2. The smallest detail visible with ground-based solar telescopes is about
   1 arc second. How large a region does this represent on the sun? (Hint:
   Use the small-angle formula, Chapter 3.)


3. What is the angular diameter of a star like the sun located 5 ly from
   Earth? Is the Hubble Space Telescope able to detect detail on the
   surface of such a star?


4. How much energy is produced when the sun converts 1 kg of mass into
   energy?


5. How much energy is produced when the sun converts 1 kg of hydrogen
   into helium? (Hint: How does this problem differ from Problem 4?)


6. A 1-megaton nuclear weapon produces about 4  1015 J of energy.
   How much mass must vanish when a 5-megaton weapon explodes?


7. A solar fl are can release 10^25 J. How many megatons of TNT would be
   equivalent?


8. The United States consumes about 2.5  1019 J of energy in all forms
   in a year. How many years could you run the United States on the
   energy released by the solar fl are in Problem 7?


9. Use the luminosity of the sun, the total amount of energy it emits
   each second, to calculate how much mass it converts to energy each
   second.


10. If a sunspot has a temperature of 4200 K and the solar surface has a
    temperature of 5800 K, how many times brighter is a square meter of
    the surface compared to a square meter of the sunspot? (Hint: Use the
    Stefan–Boltzmann law, Chapter 7.)


11. Neglecting energy absorbed or refl ected by Earth’s atmosphere, the
    solar energy hitting 1 square meter of Earth’s surface is 1370 J/s. How
    long does it take a baseball diamond (90 ft on a side) to receive 1
    megaton of solar energy?

NOAO

NASA/SOHO

166

NOAO

PART 2 | THE STARS