Flux, Magnitudes and the Distance Ladder · seed 1 · A4, ink-friendly. The answer key prints on its own page for grown-ups.

From faint glimmers to far distances

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

  1. Star A is 5 magnitudes brighter than star B. How many times brighter is it?

    • 5 times
    • 100 times
    • 2.512 times

  2. What is the difference between flux and luminosity?

    • Flux is observed power per area; luminosity is total output
    • Flux is total output; luminosity is observed per area
    • They are two names for the same quantity

  3. On the magnitude scale, a bigger number means a brighter star.

    Circle one:   True   False

  4. What is absolute magnitude?

    • How bright a star looks from Earth
    • How bright a star would look from 10 parsecs
    • How much light a telescope collects

  5. Two identical stars: B sits 3 times farther than A. How many times dimmer does B look?

    Answer: ______________

  6. How does a Cepheid variable give a distance?

    • Measure its colour and read the distance directly
    • Count its planets and apply Kepler third law
    • Time its period to get luminosity, then compare with flux

  7. The parallax calibration used by the whole ladder is found to be slightly off. What happens?

    • Only the nearest stars need new distances
    • Every rung above inherits the error and shifts
    • Cepheid distances stay exact regardless

  8. A star has apparent magnitude 10 and absolute magnitude 5. What is its distance in parsecs?

    Answer: ______________

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Answer key

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

From faint glimmers to far distances W1-mt_q1vEUas3AY-s1

  1. 100 times · Five magnitudes is defined as exactly a factor of 100.
  2. Flux is observed power per area; luminosity is total output · What reaches you spreads over a sphere, so distance separates the two.
  3. False · The scale runs backwards: brighter stars get smaller numbers.
  4. How bright a star would look from 10 parsecs · Fixing the distance lets magnitudes compare true outputs.
  5. 9 · Inverse square: 3 squared is 9.
  6. Time its period to get luminosity, then compare with flux · Period sets true wattage, and flux versus wattage gives distance.
  7. Every rung above inherits the error and shifts · Each rung is calibrated against the one below, so errors climb.
  8. 100 · The distance modulus of 5 corresponds to 100 parsecs.
Worksheet · LightMySky