Astrophysics - Cosmology

Question 1

What is the doppler effect?

Answer 1

The shift in the measured wavelength and frequency by an observer due to the relative motion between the observer, and the wave source.

Question 2

When is the redshift positive, and when is it negative?

Answer 2

Redshift is positive when an object is receding from the observer (a -ive velocity).

Redshift is negative (blue shift) when an object is approaching the observer (a +ive velocity).

Question 3

What is the equation for the Apparent wavelength in the doppler shift?

Answer 3

λ app = λ - V.T
λ app = λ - (V.λ ) / c

Question 4

What are two sources of observation of the doppler shift?

Answer 4

Absorption lines (compare their observed lines to ones measured in a lab) eg. Balmer.

Standard candles to measure the distance to distant galaxies THEN use absorption lines too calculate their relative velocities too earth.

Question 5

Are all the line shifts for the absorption lines the same?

Answer 5

The shifts are all relative and dependent on wavelength since the Z is constant for a star.

Question 6

What is Hubble’s law?

Answer 6

The rate at which the galaxy recedes is directly proportional to its distance from us.

V=Hd

H = 6.5Km.S−1.Mpc−1

Question 7

How can Hubble’s law be used to estimate the age of the universe?

Answer 7

Approximately equal to 1/H where H is in S-1 (per second)

If the universe expands uniformly

Question 8

What is the evidence for the Hot Big Bang theory?

Answer 8

Cosmological background radiation

Question 9

What disproves hubble’s model of expansion?

Answer 9

More distant objects seen to recede faster and objects appear brighter than predicted.

> > The universe is accelerating