From laboratory measurements, we know that a particular spectral line formed by hydrogen appears at a wavelength of 121.6 nanome
ters (nm). The spectrum of a particular star shows the same hydrogen line appearing at a wavelength of 121.8 nm. What can we conclude?
a) The star is moving toward us.
b) The star is moving away from us.
c) The star is getting hotter.
d) The star is getting colder.
e) The "star" actually is a planet.
If an object moves toward us, the light waves it emits are compressed - the wavelength of the light will be shorter, making the light bluer. On the other hand, if an object moves away from us, the light waves are stretched, making it redder. If from laboratory measurements we know that a specific hydrogen spectral line appears at the wavelength of 121.6 nanometers (nm) and the spectrum of a particular star shows the same hydrogen line appearing at the wavelength of 121.8 nm, we can conclude that the star is moving away from npos, since the wavelength related to that star is more expanded.
Then the rocket will slow down until the end of gas and when all the gases are ended, then it stops at the highest point of space and falls back to earth.