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Physics > Cosmology > Flashcards

Cosmology Flashcards

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1
Q

What is the astronomical unit

A

Average distance from the Earth to the Sun

(1.5 x 10^11 m)

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2
Q

When is the astronomical unit most often used

A

To express the average distance between the Sun and other planets in the Solar System

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3
Q

What is the light year

A

The distance travelled by light in a vacuum in a time of one year

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4
Q

When is the light year often used

A

When expressing distances to stars or other galaxies

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5
Q

How many arcminutes are there in 1 degree

A

60

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6
Q

How many arc seconds in one arc minute

A

60 arcsecond

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7
Q

What is the parsec

A

Distance at which a radius of one AU subtends an angle of one arcsecond

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8
Q

How can you determine the value of 1 parsec in metres

A

tan(1 arcsecond) = 1 AU / 1 pc

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9
Q

What is stellar parallax

A

A technique used to determine the distance to stars that are relatively close to the Earth, at distances less than 100 pc

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10
Q

What is Parallax

A

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

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11
Q

When can we calculate the Parallax angle

A

Using precise measurements

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12
Q

How to calculate the distance to the nearby star

A

d = 1 / p

Where p is measured in arcseconds

Limited so stars less than 100pc from the Earth

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13
Q

What is the doppler shift

A

Whenever a wave source moves relative to an observer, the frequency and wavelength of the waves received by the observer change compared with what would be observed without relative motion

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14
Q

What can the doppler effect be used to determine for a distant galaxy

A

The relative velocity

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15
Q

How can the doppler effect be used to determine the relative velocity of a distant galaxy

A

Absorption spectrum of a specific element is determined in the laboratory

Same spectrum is observed in light from a distant galaxy

Any difference in the observed wavelengths of the absorption line must be caused by the relative motion between the galaxy and the Earth

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16
Q

What happens to the absorption lines when the galaxy is moving towards the Earth

A

Absorption lines will be blue-shifted because the wavelength appears shorter

17
Q

What happens to the absorption lines when the galaxy is moving away from the Earth

A

Absorption lines will be red-shifted because the wavelength appears streched

18
Q

What happens to the absorption lines when the galaxy is moving away from the Earth

A

Absorption lines will be red-shifted because the wavelength appears stretched

19
Q

Doppler Equation

A

( change in lambda / lambda ) = ( change in frequency / frequency) = ( relative velocity / speed of light )

20
Q

Hubble’s Law

A

Recessional speed of a galaxy is almost directly proportional to its distance (d) from the earth

21
Q

What should the graph of recessional speed against distance for all galaxies look like

A

The plotted data should produce a straight line through the origin - spread in the original data points suggests that Hubble’s law is valid - but there is a large uncertainty in the value for the gradient of the best-fit line

22
Q

Hubble’s Constant

A

Gradient of the graph

v = (H (Hubble’s Constant)) x (d))

Units = s^-1 or km s^-1 Mpc^-1

23
Q

What is the cosmological principle

A

When viewed on a large enough scale, the Universe is homogenous and isotropic, and the laws of physics are universal

24
Q

What are the two key pieces of evidence for the Big Bang Theory

A

Hubble’s Law and Microwave Background Radiation

25
Q

How can the Big Bang Theory explain Background Microwave Radiation

A

When the universe was young and extremely hot - space was saturated with high-energy gamma photons

Expansion of the universe meant that space itself was stretched over time - this stretched the wavelength of these high-energy photons - explaining CBR

26
Q

What is the age of the Universe

A

d/v = 1 / Hubble’s Constant

27
Q

What is dark energy

A

Suggested that this hypothetical form of energy fills all of space and tends to accelerate the expansion of the Universe

28
Q

Changing Nature of the Universe

A

The Big Bang - Time and space are created and the universe is a singularity - it is infinitely dense and hot

10^-35s - The Universe expands rapidly, including a phase of incredible acceleration known as inflation - no matter in the Universe and full of EM radiation in the form of high energy gamma photons

10^-6s -The first fundamental particles gain mass through a mechanism that is not fully understood but involves the Higgs Boson

10^-3s - Quarks combine to form the first hadrons - most of the mass in the universe was created within the first second through the process of pair production

1s - Creation of matter stops after about 1s

100s - Protons and Neutrons duse together to form deuterium and helium nuclei - along with a small quantity of lithium and beryllium - expansion of the Universe is so rapid that no heavier elements are created - 25% of the matter in the universe is helium nuclei

380,000 years - Universe cools enough for the first atoms to form - Nuclei capture electrons - EM radiation from this stage of the universe is what can be detected as MBR

30 Million Years - First stars appear - through nuclear fusion in these stars the first heavy elements begin to form

200 Million Years - Milky Way forms as gravitational forces pull clouds of hydrogen and existing stars together

9 Billion Years - Solar System forms from the nebula left by the supernova of a larger star - Sun forms the remaining material forms the Earth and other planets

13.2 billion years - The first modern humans evolve

29
Q

How much of the universe does dark energy make up

A

68%

30
Q

How much of the universe is made up of dark matter

A

27%

Physics (19 decks)

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