Red-shift and cosmic expansion

Science · Space Systems & Earth's History · ages 15-16

Name ______________________ Date ____________

In an illustrative data set, galaxies at 100, 200 and 300 million light-years show wavelength increases of 2, 4 and 6 nm for the same line. What trend does this show?
- Red-shift increases as distance increases.
- Red-shift decreases as distance increases.
- Red-shift is steady as distance increases.
A spectral line measured at 500 nm in a lab appears at 650 nm in a galaxy's light. What has happened to this line?
- It is red-shifted because its observed wavelength is longer.
- It is blue-shifted because its wavelength is longer.
- It is unchanged because both measurements use the same unit.
Across many distant galaxies, larger distances go with larger red-shifts on average. Which explanation does this support?
- Galaxies grow larger while the gaps stay fixed.
- Distances between unbound galaxies grow as space expands.
- Light loses all its spectral lines while travelling between galaxies.
Why did establishing distances to galaxies outside the Milky Way help astronomers study expansion?
- It paired galaxy distances with measured red-shifts.
- It placed distant galaxies within our own Milky Way.
- It replaced spectral shifts with galaxy colour only.
How is a departing siren a useful but limited analogy for cosmological red-shift?
- Both result only from a source moving away through fixed space.
- Both require sound and light to have the same speed through space.
- Both involve longer observed wavelengths; their causes differ.
What is the cosmic microwave background?
- Radiation from the Sun, spread over the sky by Earth's atmosphere.
- Radiation from the early hot universe, now detected as microwaves.
- Microwaves made by stars today, spread over the sky by space dust.
Why do the distance-red-shift pattern and the cosmic microwave background together support the hot Big Bang model?
- Together they test identical predictions of the same model.
- Together they test different predictions of the same model.
- Together they end all further testing of the current model.
A red-shift from one galaxy, by itself, proves that space is expanding.
Circle one: True False

Answer key

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

Red-shift and cosmic expansion W1-mt_JeAfpxw49W-s1

Red-shift increases as distance increases. · As distance increases from 100 to 300 million light-years, the wavelength increase grows from 2 to 6 nm.
It is red-shifted because its observed wavelength is longer. · 650 nm is longer than 500 nm. A line shifted to a longer wavelength is red-shifted.
Distances between unbound galaxies grow as space expands. · Expansion increases distances between galaxies not held together by gravity and stretches light travelling between them.
It paired galaxy distances with measured red-shifts. · Distances and red-shifts together let astronomers identify the distance-recession pattern.
Both involve longer observed wavelengths; their causes differ. · A departing siren changes the spacing of arriving sound waves through source motion. Cosmic expansion stretches light during its journey.
Radiation from the early hot universe, now detected as microwaves. · The hot Big Bang model predicts radiation left from the early hot universe. Expansion stretches it to microwave wavelengths.
Together they test different predictions of the same model. · The observations test different predictions of the same model. Their agreement strengthens support without ending further testing.
False · An individual galaxy's own motion can produce red-shift. The expansion evidence is a pattern across many galaxies, not one shift alone.