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Flashcards in Chapter 12 Deck (22)
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1
Q

What does the brightness of a star depend on?

A
  1. Luminosity (how much light energy it gives out in given time)
  2. Distance from observer
2
Q

What is a star’s apparent magnitude?

A

How bright a star looks when seen from Earth

3
Q

What is a star’s absolute magnitude?

A

How bright a star really is regardless of observed brightness.

4
Q

How is the distance from the earth to a star measured?

A

Using the apparent magnitude and absolute magnitude of a star.

5
Q

What are standard candles and why are they significant?

A

Objects that you can measure the brightness of directly.

The method used for finding distances to stars from the earth using their apparent and absolute magnitude only works for standard candles.

6
Q

Give an example of a standard candle

A

Cepheid variable stars whose brightness changes in a certain pattern.

Finding a Cepheid variable within a galaxy allows us to measure the distance of that galaxy from us.

7
Q

Kepler’s Third Law

A

T^2 is proportional to R^3

8
Q

Radar velocity ratio

A

v/c = Tback - Tout/ Tback + Tout

v/c =T2 - T1/ T2 +T1

9
Q

Two way radar pulses derivation

A

v/2 (T2 +T1) =c/2 (T2- T1)

T2/T1 = 1 + (v/c) / 1 - (v/c)

10
Q

What is the k factor?

A

One way doppler shift.

Factor by which wavelength is shifted one way.

11
Q

What is the k^2 factor

A

2 way doppler shift.

Factor by which wavelength is shifted in 2 ways.

12
Q

What is the doppler effect?

A

Change in frequency of a wave due to the relative motion of the source and the observer.

13
Q

Difference between cosmological and doppler red shift

A

Cosmological: Light from distant galaxies is redshifted due to wavelength stretching in an expanding universe. Space itself is expanding.

Doppler: Due to relative motion of observer and source.
- moving through space.

14
Q

What does the redshift of spectra from galaxies give?

A

The recessional velocity

15
Q

Hubble’s law

A

V = H d

16
Q

Unit of H0 in hubble’s law?

A

S^-1

17
Q

What is the significance of hubble’s constant?

A

Rate of expansion of the universe depends on this constant.

18
Q

How to determine the age of the universe

A

t = 1/H

assuming that universe has been expanding at the same rate for its whole life.

19
Q

What is the size of the observable universe?

A

Absolute size is unknown and changing.

Observable universe is a sphere with Earth at the centre with a radius that equal to the maximum distance that light can travel during the universe’s age.

20
Q

Redshift as evidence of big bang

A

Redshift shows that most celestial objects are moving away from us.

Therefore, extrapolating backwards, universe must have started at a single point.

21
Q

Cosmic Microwave Background Radiation

A

After 300,000 years the universe became transparent since photons no longer lost energy through collisions as the temperature dropped significantly allowing nuclei and electrons to form.

Because the universe has expanded, the wavelengths of this CMBR have been stretched and are now in the microwave region.

22
Q

CMBR as evidence for big bang

A

Uniform radiation which shows evidence of a uniform and HOT source.