Cosmology

Question 1

cosmological principle

Answer 1

on a large scale the universe is uniform
homogenous (the same everywhere)
isotropic (same in every direction)
and has universal laws of physics

Question 2

evidence for the big bang (3)

Answer 2

Redshift of galaxies
Cosmic microwave background
Primordial Helium

Question 3

Explain how redshift shows evidence for the big bang

Answer 3

the universe is expanding
meaning it was smaller and denser in the past
Hubbles law indicates that galaxies are receding from us

Question 4

Explain how cosmic microwave background radiation shows evidence for the big bang

Answer 4

space is filled with radiation at 2.7K
best explanation is that it is left over from the dense state
radiation started as gamma rays and has been redshifted to mircowaves as the universe has expanded

Question 5

Explain how primodial helium shows evidence for the big bang

Answer 5

25% of the universe is helium
the amount of He cannot be explained by stellar nucleosynthesis
can be explained if it was made during an early hot dense state of the entire universe

Question 6

Hubble’s law

Answer 6

the recession velocity of a distant galaxy is directly proportional to its distance from the observer
v=H0d
v = kms^-1
H0=kms^-1Mpc^-1
d=Mpc

Question 7

Explain the energy transfers occurring in a nebula

Answer 7

GPE to KE and thermal
Hydrogen burning causes thermal energy to be produced
the heat causes an outward pressure which opposes the gravity

Question 8

Explain what happens in a main sequence star

Answer 8

the surface cools and expands because the hydrogen runs out and the helium burns but it needs more energy than H

Question 9

Explain what happens in a red giant

Answer 9

it is an expanded main sequence star made from hydrogen when the He runs out a white dwarf forms

Question 10

Explain what a Planetary Nebula is

Answer 10

layers of H and He with an Fe core, in a supernova other elements are formed

Question 11

Explain what happens in a white dwarf

Answer 11

Fermi pressure; when atoms are compressed pressure forms because the individual atoms cannot be compressed further

Question 12

What is a Neutron star

Answer 12

just made from neutrons

Question 13

Assumptions for Olbers paradox

Answer 13

the universe is static

the universe is infinite in space

Question 14

assumptions of the universe

Answer 14

the universe is infinite in time

the universe is homogenous

Question 15

state Olbers’ paradox

Answer 15

if stars are distributed evenly throughout the universe the night sky should be as bright as the day because there is a visible star in every direction , so every line of light lands on a star

Question 16

Why is Olbers’ paradox wrong

Answer 16

it’s dark at night

everything would be as hot as and as bright as the surface of a star

Question 17

what is 1 light year

Answer 17

the distance travelled by light in one year

9.5x10^15

Question 18

what is one astronomical unit

Answer 18

the mean distance from the centre of the sun to the centre of the earth
1.5x10^11

Question 19

what is one parsec

Answer 19

the distance to an object with a parallax of 1 arc second across a baseline of 1AU
3.1x10^16m or 3.3 light years

Question 20

parallax formula

Answer 20

distance in parsec = 1/parallax in arc seconds

Question 21

Doppler effect

Answer 21

the change in wavelength or frequency due to motion of the source of the wave

Question 22

continuous spectrum

Answer 22

an emission spectrum which contains a range of all wavelengths

Question 23

how does an absorption line occur

Answer 23

photons are absorbed by an electron in an atom

line occurs when the energy is re-radiated with a narrow frequency

Question 24

Three theories of the fate of the universe

Answer 24

if the density is higher than the critical density it is a closed universe. meaning gravity will be strong enough to cause a big crunch
if density is equal to the critical density then it is flat. meaning the rate of expansion with tend to zero
if the density is lower than the critical density then it is an open universe. meaning the gravitational force is not strong enough and will cause the universe to expand forever causing a big freeze

Question 25

what does our solar system consist of

Answer 25

Sun planets planetary satellites and comets

Question 26

critical density

Answer 26

the minimum density that ensures that the Universe could not expand forever, but will not collapse back on itself either

Question 27

what do scientists believe will be the fate of the solar system

Answer 27

the density is close to or almost equal to the critical density meaning it is a flat universe

Question 28

Three ‘facts’ contradicting Olbers’ paradox

Answer 28

the universe is finite in size
the universe is not static it is expanding (Evident from redshift from distant galaxies)
finite age of the universe means that light from distant stars has not reached us yet