Module 5 - 5.5.3 Cosmology

Question 1

The Astronomical Unit (definition)

Answer 1

The mean distance from the centre of the Earth to the centre of the Sun
1AU = 1.5x10^11m

Question 2

The Light Year (definition)

Answer 2

The distance travelled by light in one year

Question 3

1 degree = – arcminutes

Answer 3

60

Question 4

The Parsec (definition)

Answer 4

A unit of distance that gives a parallax angle of 1 second of an arc using the radius of the Earth’s orbit (1AU) as the baseline of a right-angled triangle

Question 5

for small angles, tan(p) =

Answer 5

p

Question 6

Stellar Parallax (definition)

Answer 6

The apparent shifting in a position of a star viewed against a background of distant stars when viewed from different positions of the Earth, such as at different positions of the Earth’s orbit

Question 7

Stellar parallax can be used to measure (2)

Answer 7

• the distance to nearby stars
• involves observing how the position of a nearby star changes over a period of time against a fixed background of stars

Question 8

A nearby star will have a — parallax angle

Answer 8

larger

Question 9

The Doppler Effect (definition)

Answer 9

The apparent shift in wavelength/frequency caused by the relative motion between a wave source and an observer

Question 10

The Doppler Effect: wavelength if the wave source is moving
- towards an observer
- away from an observer

Answer 10

• shorter
• longer

Question 11

Red Shift (definition)

Answer 11

The apparent increase in wavelength of em radiation caused when the source is moving away, relative to an observer

Question 12

The Doppler Effect in stars (4)

Answer 12

• compare the light spectrum produced from the Sun with that of a distant galaxy
• the pattern of lines is shifter towards the red end of the spectrum for stars travelling away from us
• known as red shift
• this is evidence that distant galaxies are moving away from us

Question 13

Red Shift is more pronounced for (2)

Answer 13

• galaxies that are further away
• Hubble concluded that galaxies which are further away from Earth are moving faster than galaxies which are closer

Question 14

Hubble’s Law

Answer 14

The recessional velocity of a galaxy is proportional to its distance from Earth

Question 15

Recessional Velocity (definition)

Answer 15

The velocity of an object moving away from an observer

Question 16

Estimating the Age of the Universe, use

Answer 16

t = 1/H0

Question 17

Olber’s Paradox (definition)

Answer 17

An argument in astrophysics that says the darkness of the night sky conflicts with the assumption of an infinite and eternal static universe

Question 18

Cosmic Background Radiation (definition)

Answer 18

Microwave radiation received from all over the sky originating from the early stages of the universe after the Big Bang

Question 19

Astronomers found that Microwave Background Radiation has a peak wavelength corresponding to a temperature of

Answer 19

2.7K

Question 20

Microwave Background Radiation has (2)

Answer 20

• the exact profile expected to be emitted from a hot body that has cooled down over a very long time
• is uniform

Question 21

Origins of Microwave Background Radiation (4)

Answer 21

• according to the Big Bang Theory, in the early stages of the Universe, matter and antimatter annihilated
• this produced lots of gamma photons (em radiation)
• this radiation has expanded with the expansion of the Universe
• is now in the microwave region of the EM spectrum

Question 22

The Big Bang Theory (definition) (3)

Answer 22

• the universe was created from a hot singularity which was infinitely dense, hot and small where all of the Universe’s current mass was situated
• there was a giant explosion known as the Big Bang
• time and space were created at this instant

Question 23

Steady State Theory (definition)

Answer 23

The Universe was static and had always existed and that matter was continually being generated from nothing to account for the expansion of the Universe

Question 24

General Relativity (definition)

Answer 24

Space and time are connected together a space-time, a property that connects the three dimensions of space and a fourth dimension of time

Question 25

Outcomes for the Future of the Universe: Density is too high (3)

Answer 25

• closed universe
• density so high that gravitational forces will prevent galaxies going on out into space forever
• instead they will slow down, stop and eventually collapse in on itself in the Big Crunch

Question 26

Outcomes for the Future of the Universe: Density is too low (3)

Answer 26

• open universe
• each galaxy will reach a constant velocity when sufficiently far apart from one another for the gravitational force on each to be negligible
• galaxies will continue to separate forever, cooling down as they do

Question 27

Outcomes for the Future of the Universe: Density if exactly the critical density (4)

Answer 27

• flat universe
• universe will expand, decreasing in velocity as it does
• it will eventually reach a final finite size after an infinite amount of time
• meaning galaxies will gradually slow down but never stop

Question 28

Dark Matter (definition)

Answer 28

Matter which cannot be seen and that does not emit or absorb electromagnetic radiation
(scientists know it exists, but don’t know where it came from)

Question 29

Detection of Dark Matter (2)

Answer 29

• cannot be detected directly through telescopes
• detected indirectly based on its gravitational effects relating to other galaxies

Question 30

Dark Energy (definition)

Answer 30

A type of energy that permeates the whole universe and opposes the attractive force of gravitation between galaxies via the exertion of a negative pressure

Question 31

Detection of Dark Energy

Answer 31

cannot be detected easily