The Cosmic Microwave Background and the Light Elements · seed 1 · A4, ink-friendly. The answer key prints on its own page for grown-ups.

Afterglow and ashes of the hot start

Science · Astronomy & Astrophysics · ages 21-22
Name ______________________   Date ____________

  1. When was the background light released?

    • When the first stars ignited
    • When the Sun was born
    • When atoms first formed, about 380,000 years after the start

  2. What is the temperature of the background glow today?

    • 273 degrees above absolute zero
    • 2.7 degrees above absolute zero
    • 2700 degrees above absolute zero

  3. The background spectrum is the most perfect blackbody ever measured.

    Circle one:   True   False

  4. About how much ordinary mass ended up as helium in the first minutes?

    • About a quarter
    • Almost all of it
    • Almost none of it

  5. Why is the glow in microwaves instead of orange light?

    • Dust painted it a new color
    • Expansion stretched the original glare a thousandfold
    • Stars absorbed the orange part

  6. What do the ripples of one part in a hundred thousand mark?

    • Scratches on the telescope mirror
    • Signals from nearby radio stations
    • The seeds that gravity grew into galaxies

  7. A student claims the helium was all forged inside later stars. What is wrong?

    • The quarter share was fixed in the first minutes, before stars
    • Stars forge no elements at all
    • Helium cannot survive inside stars

  8. A student says scattered starlight could explain the glow. What rules that out?

    • Starlight is too bright to scatter
    • Scattered starlight cannot fake both the spectrum and the uniformity
    • Stars did not exist in the past
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Answer key

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

Afterglow and ashes of the hot start W1-mt_oz0MJXiuVt-s1

  1. When atoms first formed, about 380,000 years after the start · Forming atoms let light travel freely for the first time.
  2. 2.7 degrees above absolute zero · Expansion cooled the original glare to just 2.7 degrees.
  3. True · That perfection matches a hot dense origin exactly.
  4. About a quarter · Cooling stopped the furnace with helium near a quarter.
  5. Expansion stretched the original glare a thousandfold · Stretching light to longer waves cools its color.
  6. The seeds that gravity grew into galaxies · Faint patches gave gravity something to amplify.
  7. The quarter share was fixed in the first minutes, before stars · The universe wide share predates every star.
  8. Scattered starlight cannot fake both the spectrum and the uniformity · Only a hot dense origin predicts both signatures together.
Worksheet · LightMySky