Homework 5

Homework 5

Due at the end of morning class on Monday, 8/2/99.

  1. Review #1, P. 338. Luminosity and distance. (Also accept absolute mag. & distance.)

  2. Review #3, P. 338. Temperature alters the spectra. Collisions with atoms and photons in gases cause atomic electrons to change energy levels, giving rise to absorption/emission spectral lines. The energy in such collisions changes with temperature (recall that at higher temps, particles move faster), so different atomic transitions are caused by collisions in gases of different temperatures.

  3. Thought #12, P. 338. Consult the table on p.332. Look for the spectral class nearest the peak in the line(s) listed in each part of the problem.
    a) A-type;
    b) O-type;
    c) G-type;
    d) accept either M- or K-type

  4. Review #2, p. 358.

    i) visual binary: pair of stars that orbits each other and can be resolved as separate objects with the eyes or with telescopes


    ii) spectroscopic binary: pair of orbiting stars that cannot be resolved as seperate objects with telescope; Doppler shifts in two stars' absorption lines tell us there are two orbiting stars

    iii)eclipsing binaries: the smaller of the two orbiting stars moves behind the larger, blocking light from the small star; this alters the light Earth receives from the system, so the LIGHT CURVE (amount of light seen vs. time) shows less light, then more light, then less light, etc.

  5. Thought #9, p. 358. We see most visual binaries as such because their member stars are far apart; spectroscopic binaries, however, are closer together. And, as Kepler says, objects that are closer together have shorter orbital periods.

  6. Thought #11, p. 358.
    a) we have to be looking at eclipsing binaries nearly edge-on, which isn't as likely as seeing them at other angles

    b) same reason

    c) at large distances, it's harder to see that two separate objects are distinct (to RESOLVE them); hence, at larger distances, one only sees visual binaries when orbiting stars are very far apart -- if stars are close, they're more likely to be seen as spectroscopic binaries

  7. Review #5, p. 373.

    a) parallax (from opposite sides of Earth), or radar
    b) parallax (from opposite sides of Sun)
    c) RR Lyrae or Cepheid variables
    d) main sequence fitting, or "spectroscopic parallax"

  8. Thought #14, p. 394. The short-wavelength light that causes sun burns is absorbed by the atmosphere when the Sun is nearer the horizon in the late afternoon. But the long-wavelength IR (infrared) radiation is not absorbed so well, meaning the Sun is still hot.

  9. Thought #16, p. 394. Smog scatters (redirects) and absorbs light that would normally travel from a distant object to your eye. So you can't see distant objects as well.

  10. Review #7, p.414. From the Doppler shifts caused by these planets' gravitational pulls on the stars they orbit.