Cosmology Flashcards
What is the astronomical unit
Average distance from the Earth to the Sun
(1.5 x 10^11 m)
When is the astronomical unit most often used
To express the average distance between the Sun and other planets in the Solar System
What is the light year
The distance travelled by light in a vacuum in a time of one year
When is the light year often used
When expressing distances to stars or other galaxies
How many arcminutes are there in 1 degree
60
How many arc seconds in one arc minute
60 arcsecond
What is the parsec
Distance at which a radius of one AU subtends an angle of one arcsecond
How can you determine the value of 1 parsec in metres
tan(1 arcsecond) = 1 AU / 1 pc
What is stellar parallax
A technique used to determine the distance to stars that are relatively close to the Earth, at distances less than 100 pc
What is Parallax
Apparent shift in the position of a relatively close star against the backdrop of much more distant stars as the Earth orbits the Sun
When can we calculate the Parallax angle
Using precise measurements
How to calculate the distance to the nearby star
d = 1 / p
Where p is measured in arcseconds
Limited so stars less than 100pc from the Earth
What is the doppler shift
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
What can the doppler effect be used to determine for a distant galaxy
The relative velocity
How can the doppler effect be used to determine the relative velocity of a distant galaxy
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
What happens to the absorption lines when the galaxy is moving towards the Earth
Absorption lines will be blue-shifted because the wavelength appears shorter
What happens to the absorption lines when the galaxy is moving away from the Earth
Absorption lines will be red-shifted because the wavelength appears streched
What happens to the absorption lines when the galaxy is moving away from the Earth
Absorption lines will be red-shifted because the wavelength appears stretched
Doppler Equation
( change in lambda / lambda ) = ( change in frequency / frequency) = ( relative velocity / speed of light )
Hubble’s Law
Recessional speed of a galaxy is almost directly proportional to its distance (d) from the earth
What should the graph of recessional speed against distance for all galaxies look like
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
Hubble’s Constant
Gradient of the graph
v = (H (Hubble’s Constant)) x (d))
Units = s^-1 or km s^-1 Mpc^-1
What is the cosmological principle
When viewed on a large enough scale, the Universe is homogenous and isotropic, and the laws of physics are universal
What are the two key pieces of evidence for the Big Bang Theory
Hubble’s Law and Microwave Background Radiation
How can the Big Bang Theory explain Background Microwave Radiation
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
What is the age of the Universe
d/v = 1 / Hubble’s Constant
What is dark energy
Suggested that this hypothetical form of energy fills all of space and tends to accelerate the expansion of the Universe
Changing Nature of the Universe
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
How much of the universe does dark energy make up
68%
How much of the universe is made up of dark matter
27%
