ASTRO 103

• Due: Feb 05
• Problems:
  • Chapter 1, Problem 7: Jupiter's moon Callisto orbits it at a distance of 1.88 million km. Its orbital period about the planet is 16.7 days. What is the mass of Jupiter? (Assume that Callisto's mass is negligible compared with that of Jupiter.) Use the modified version of Kepler's third law (Section 1.7).

  • Chapter 2, Problem 4: The black-body emission spectrum of object A peaks in the ultraviolet region of the electromagnetic spectrum, at a wavelength of 200 nm. That of object B peaks in the red region at 650 nm. According to Wien's law, A is how many times hotter than B? According to Stefan's law, A is radiating how much more energy per unit area per second?

    BE SURE TO SHOW ALL YOUR WORK for both problems.

Assignment #2

• Due: Feb 26
• Problems:
  • Chapter 10, Problem 4: Two stars--A and B, of luminosities 0.5 and 4.5 times the luminosity of the Sun, respectively--are observed to have the same apparent brightness. Which one is more distant, and how much farther away is it than the other?

  • Chapter 11, Problem 4: The intensity of a beam of light shinning through a dense molecular cloud is diminished by a factor of 2.5 for every 3 pc the beam travels. By what total factor is the intensity reduced if the total thickness of the cloud is 30 pc? What is the change in magnitudes?

    BE SURE TO SHOW ALL YOUR WORK for both problems.

Assignment #3

• Due: Mar 05
• Problems:
  • Chapter 9, Problem 8: How long does it take the Sun to convert one Earth mass of hydrogen to Helium?

  • Chapter 12, Problem 6: A certain telescope could just detect the Sun at a distance of 10,000 pc. What is the maximum distance at which it could detect a nova having a peak luminosity of 10⁵ solar luminosities? Repeat the calculation for a supernova having a peak luminosity of 10¹⁰ times that of the sun.

    BE SURE TO SHOW ALL YOUR WORK for both problems.

Assignment #4

• Due: Apr 02
• Problems:
  • Chapter 14, Problem 4: The Hubble Space Telescope can just detect a star like the Sun at a distance of 100,000 pc. The brightest Cepheids have luminosities 30,000 times greater than that of the Sun. How far away can HST see these Cepheids?

  • Chapter 14, Problem 8: A density wave made up of two spiral arms is moving through the Galactic disk. At the 8-kpc radius of the Sun's orbit around the Galactic center, the wave's speed is 120 km/s, and the Galactic rotation speed is 220 km/s. Calculate how many time the Sun has passed through a spiral arm since the Sun formed 4.6 billion years ago.

    BE SURE TO SHOW ALL YOUR WORK for both problems.

Assignment #5

• Due: Apr 09
• Problems:
  • Chapter 14, Problem 6: Calculate the total mass of the Galaxy lying within 20 kpc of the center if the rotation speed at that radius is 240 km/s.

  • Chapter 15, Problem 5: Two galaxies are orbiting one another at a separation of 500 kpc. Their orbital period is estimated to be 30 billion years. Use Kepler's third law (as stated in Chapter 14) to find the total mass of the pair. (See Section 14.5).

    BE SURE TO SHOW ALL YOUR WORK for both problems.

Assignment #6

• Due: Apr 30
• Problems:
  • Chapter 13, Problem 7: Supermassive black holes are believed to exist in the centers of some galxies. What would be the Schwarzschild radii of black holes of 1 million and 1 billion soloar masses? How does the first black hole compare in size with the Sun? How does the second compare in size with the solar system?

  • Chapter 16, Problem 1: A Seyfert galaxy is observed to have broadened emission lines indicating a speed of 1000 km/s at a distance of 1 pc from its center. Assuming circular orbits, use Kepler's laws (Section 14.6) to estimates the mass wihtin this 1-pc radius.

    BE SURE TO SHOW ALL YOUR WORK for both problems.

Assignment #7

• Due: May 07
• Problems:
  • Chapter 17, Problem 5: For H₀ = 65 km/s/Mpc, the critical density is 10^-26 kg/m³. (a) How much mass does that correspond to in a volume of 1 A.U.³? (b) How large a cube would be required to enclose 1 Earth mass of material?

  • Chapter 17, Problem 7: Assuming the critical density and using the distances presented in Table 16.1, estimate the total amount of matter in the observable universe. Express you answers (a) in kilograms, (b) in solar units, and (c) in "galaxies," where 1 galaxy = 10¹² solar masses.

    BE SURE TO SHOW ALL YOUR WORK for both problems.