How does light from distant stars show how fast they are moving away from us.

When an ambulance drives away from you it has a lower pitch than when it is stationary. The faster the ambulance drives away from you the lower the pitch of it's siren will be. This is called the Doppler effect and it occurs with light too. When a galaxy moves away from us, it's light is shifted towards the red part of the spectrum, we call this redshift. Since all galaxies have abundant hydrogen, we can compare the wavelength of their hydrogen emission lines (red shifted light) with the same hydrogen emission lines that we have found in the lab to determine the change in wavelength between the emission lines, and hence determine the speed the galaxy is receding from us. We can then use the following equation to find that speed: v=c*(change in wavelength/wavelength in lab), where v is the speed the galaxy is receding from us and c is the speed of light.

NR
Answered by Nicholas R. Physics tutor

2016 Views

See similar Physics A Level tutors

Related Physics A Level answers

All answers ▸

A nucleus of the stable isotope Pb(208,82) has more neutrons than protons. Explain why there is this imbalance between proton and neutron numbers by referring to the forces that operate within the nucleus.


If the highest frequency a song is 10 kHz and it is encoded at 16 bits per sample what is the minimum number of bytes needed to encode the 3 minute song?


what is the scape velocity?


The mercury atoms in a fluorescent tube are excited and then emit photons in the ultraviolet region of the elecrtomagnetic spectrum. Explain how the mercury atoms become excited.


We're here to help

contact us iconContact ustelephone icon+44 (0) 203 773 6020
Facebook logoInstagram logoLinkedIn logo

MyTutor is part of the IXL family of brands:

© 2025 by IXL Learning