2.7 Astronomy

Question 1

What is the doppler effect?

Answer 1

The apparent change in the frequency / wavelength of a wave when there is relative motion between the source and the observer is called the Doppler effect.

Question 2

What is cosmological red shift?

Answer 2

Cosmologists think of the expanding universe as the expansion of space itself. So light waves from a distant galaxy are being stretched as the space between us and that galaxy increases. This is called cosmological red shift to distinguish it from red shift produced by sources that are moving through space.

Question 3

What is the difference between cosmological red shift and doppler shift?

Answer 3

Doppler shift is due to the relative speed between the observer and the source. Cosmological redshift is due to the expansion of the space between the observer and the source.

Question 4

What would an increase in wavelength cause the sign of z to be?

Answer 4

Positive. A positive sign for z will indicate to us the source is moving away relative to the observer (we would also get a positive v as well!!).