Question

How do you describe the Doppler effect and how it relates to the distance of a galaxy from Earth?

Answer 1

The Doppler effect in astronomy refers to the redshift seen when galaxies move away from Earth, indicating an expanding universe. Hubble's observations led to the formulation of the Hubble's Law, which correlates redshift with galaxy distance, confirming this expansion.

Step-by-step explanation:

The Doppler effect is a change in the frequency or wavelength of a wave in relation to an observer who is moving relative to the wave source. In astronomy, it's used to deduce the motion of galaxies. If a galaxy is moving away from Earth, its light is redshifted - its wavelength is stretched out, making it appear redder than normal. This effect, first noted by Edwin Hubble, indicates that the universe is expanding. Galaxies farther away exhibit greater redshifts, meaning they move away faster. Using the relativistic Doppler effect, which accounts for velocities close to the speed of light, we can also estimate the distance of these galaxies from Earth. With the help of tools like the Hubble Space Telescope, scientists can measure the orbital speed of the gas around quasars, using the Doppler effect, to determine their mass. The correlation between redshift and distance forms the basis of Hubble's Law, which played a pivotal role in our understanding of the expanding universe.

Answer 2

When the siren of an ambulance approaches you, the pitch suddenly drops as it passes by. This is because as the ambulance approaches you, the sound waves are being squeezed together, so you hear a higher pitch. After the ambulance passes by, the sound waves are receding.

This apparent change in the pitch (or frequency) of sound is known as the Doppler shift. Light from distant stars and galaxies can be shifted in the same way. A red shift indicates that a galaxy is moving away from us, while a blue shift indicates that the galaxy is moving towards us.