Stellar Spectra, Spectral Classes and Surface Composition · seed 1 · A4, ink-friendly. The answer key prints on its own page for grown-ups.

Reading starlight line by line

Science · Astronomy & Astrophysics · ages 20-21
Name ______________________   Date ____________

  1. Classes run O, B, A, F, G, K, M. What does the order track?

    • Youngest to oldest
    • Nearest to farthest
    • Hottest to coolest

  2. What does the overall colour and peak of the continuum record?

    • The temperature of the emitting layers
    • The exact chemical recipe of the star
    • How far away the star sits

  3. Hydrogen lines are strongest in the hottest O stars, since those hold the most hydrogen.

    Circle one:   True   False

  4. Which effects broaden a spectral line?

    • Distance, age, and mass of the star
    • Thermal motion, pressure, and rotation
    • Telescope size, exposure time, and pixel count

  5. Why is Balmer absorption strongest in A stars?

    • A stars contain far more hydrogen than other stars
    • Only A stars have any electrons at all
    • The first excited level is well populated only at middle temperatures

  6. How do broadening and shifting differ on a plotted profile?

    • Broadening moves the line; shifting smears it
    • They look identical and cannot be separated
    • Broadening smears the line; shifting moves the whole line

  7. A student points at a red continuum and claims the star is hydrogen poor. What is the mistake?

    • Red stars cannot be observed at all
    • Hydrogen has no spectral lines
    • Colour gives temperature, not composition; lines give composition

  8. A line is shifted red but keeps its normal width. What do you conclude?

    • The star spins much faster than normal
    • The star moves away; its gas churns as usual
    • The star is much hotter than normal
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Answer key

For grown-ups. Fold this page away before handing over the rest.

Reading starlight line by line W1-mt_4FBh5G7Gdc-s1

  1. Hottest to coolest · The letters sort stars by surface temperature from hot to cool.
  2. The temperature of the emitting layers · The smooth glow is thermal, so its shape means heat.
  3. False · O stars ionise hydrogen away; the lines peak in middle A stars.
  4. Thermal motion, pressure, and rotation · Churning and collisions smear the line symmetrically.
  5. The first excited level is well populated only at middle temperatures · Hotter stars ionise hydrogen; cooler ones trap it in the ground state.
  6. Broadening smears the line; shifting moves the whole line · Width means churn in the gas; a red or blue move means bulk motion.
  7. Colour gives temperature, not composition; lines give composition · The red glow means cool; only line strengths speak of recipe.
  8. The star moves away; its gas churns as usual · The shift shows motion away while unchanged width shows normal churn.
Worksheet · LightMySky