Cosmology

Question 1

What are the 3 main specialist measurements for distance in space?

Answer 1

astronomical unit (AU), light years and parsec

Question 2

What is an AU?

Answer 2

It is the distance from Earth to Sun, 1.5 x 10^11

Question 3

What is a light year?

Answer 3

Distance travelled by light in a vacuum in one year, 9.46 x 10^15

Question 4

What is a parsec?

Answer 4

The distance at w hich a radius of 1 AU subtends an angle of 1 arcsecond, 3.1 x 10^16

Question 5

How many arcminutes are in 1 degree?

Answer 5

60 arcminutes

Question 6

How many arcseconds in 1 arcminute?

Answer 6

60 arseconds

Question 7

What is 1 arcsecond in degrees?

Answer 7

1/3600

Question 8

What is the equation with arcsecond, AU and parsecs

Answer 8

tan(1 arcsecond) = 1 AU/1 pc

Question 9

What is stellar parallax?

Answer 9

A technique used to determine the distance to stars that are relatively close to the Earth by comparing their apparent positions against distant stars at times 6 months apart

Question 10

What is parallax?

Answer 10

The apparent shift in the position of a relatively close star against the backdrop of more distant stars as the Earth orbits the Sun

Question 11

What is the equation to calculate the parallax angle, and what units must each quantity be in?

Answer 11

p = 1/d, where p is the parallax angle measured in arcseconds, and d is the distance to the nearby star measured in parsecs

Question 12

What is the Cosmological Principle?

Answer 12

The assumption that the universe is homogeneous, isotropic, and the laws of physics are universal

Question 13

What does homogeneous mean?

Answer 13

Matter is distributed uniformly across the universe

Question 14

What does isotropic mean?

Answer 14

The universe looks the same in all directions to every observer

Question 15

What is the Doppler effect?

Answer 15

The change in frequency and wavelength of waves received from an object moving relative to an observer compared with what would be observed without relative motion

Question 16

What change in wavelength is observed on the absorption lines in a spectra when a galaxy is moving towards earth?

Answer 16

The absorption lines will be blue-shifted - they move towards blue end of the spectrum

Question 17

What change in wavelength is observed on the absorption lines in a spectra when a galaxy is moving away from earth?

Answer 17

The absorption lines will be red-shifted

Question 18

What is the Doppler equation?

Answer 18

Δλ/λ = Δf/f = v/c
where λ is the source wavelength
f is the source frequency

Question 19

What is Hubble’s Law?

Answer 19

The recessional speed, v, of a galaxy is almost directly proportional to its distance, d, from earth

Question 20

What is the equation from Hubbles law?

Answer 20

v = H0 x d
where H0 is Hubble’s constant

Question 21

What is the model of the expanding universe?

Answer 21

It states that the fabric of space, and time, is expanding in all directions

Question 22

What is Hubble’s Law key evidence for?

Answer 22

The Bing Bang Theory, and the model of the expanding universe

Question 23

What is the Big Bang Theory

Answer 23

The theory that at a moment in the past all the matter in the universe was contained in a singularity, the beginning of space and time, that expanded rapidly outwards

Question 24

What are the 2 key pieces of evidence for the Big Bang Theory?

Answer 24

Hubble’s Law and microwave background radiation

Question 25

How does Hubble's Law provide evidence for the Big Bang?

Answer 25

Hubble's Law shows that the universe is expanding. If we could run time backwards, the Universe would keep shrinking, getting smaller, denser and hotter, until it collapses into a singularity, that, according to the Big Bang Theory, expanded into the universe

Question 26

What is microwave background radiation?

Answer 26

The microwave signal of uniform intensity detected from all directions of the sky

Question 27

What two ways does microwave background radiation provide evidence for the Big Bang?

Answer 27

1. At the beginning, space was saturated with high energy gamma photons. As universe expanded, space itself stretched over time, stretching the gamma photons which can now be observed as microwaves 2. Universe was extremely hot at the beginning. Over time, temperature reduced to 2.7K. Universe may be treated as black body radiator - at this temperature, peak wavelength is in microwave region

Question 28

How can you calculate the age of the universe?

Answer 28

age of Universe, t = 1/H0 where H0 is Hubble's constant in units s^-1

Question 29

Describe the history of the universe, from formation to now

Answer 29

10^-35: rapid expansion, earth full of EM radiation - gamma radiation - and energy. No matter 10^-6: first fundamental particles gain mass 10^-3: first hadrons (protons, neutrons) formed. Most mass formed through pair production 1s: Matter stops being created 100s: Lighter nuclei start forming (deuterium, helium, lithium, beryllium). 25% of matter is helium nuclei 38000 years: atoms start forming 30 million years: first stars form

Question 30

What causes the expansion of the universe to accelerate?

Answer 30

Dark energy

Question 31

How much of our universe is dark energy predicted to make up?

Answer 31

68% of our universe

Question 32

What is dark matter?

Answer 32

A hypothetical form of matter spread throughout the galaxy that neither emits nor absorbs light

Question 33

What could dark matter provide an explanation for?

Answer 33

The differences between predicted and observed velocities of stars in galaxies