Question

Laboratory measurements show that a sample of a particular gas shows a spectral line at a wavelength of 424 nanometers. If we observe a nearby galaxy and find the same spectral line at a wavelength of 421 nanometers, what can we conclude?

(a) The galaxy is moving toward us.
(b) The galaxy is moving away from us.
(c) The galaxy is hotter than the laboratory sample of hydrogen.
(d) The galaxy is colder than the laboratory sample of hydrogen.
(e) The galaxy is very young.

Answer 1

The galaxy with a spectral line at 421 nm, compared to the original 424 nanometers, is moving toward us as indicated by the shorter observed wavelength.

Step-by-step explanation:

When observing spectral lines from a distant galaxy, if the lines are shifted from their normal position in a laboratory setting, this indicates a Doppler effect. A spectral line observed at a shorter wavelength than the original indicates the object is moving toward us, known as a blue shift.

In the case of the galaxy with a spectral line at 421 nm where the original wavelength is 424 nanometers, the galaxy is moving toward us because the observed wavelength is shorter than the wavelength measured in the laboratory.