cosmology Flashcards
Electron energy levels
> all are negative
level n=1 is ground state
ionisation energy will completely remove electron from the atom
Excitation
> move from low to high electron level by absorbing a photon
photon absorbed must have exactly the excitation energy
De-excitation or relaxation
> go down energy levels by emitting a photon
photon energy is equal to difference between energy levels transitioned between
Spectra
> Continuous: contains all colours, wavelengths and frequencies.
Emission line: series of narrow, bright, coloured lines on a dark background.
Absorption: narrow dark lines on continuous spectrum background.
Diffraction grating
> contains thousands of narrow slits
equal width and spaced lines
path difference in general is nλ
phase diff =0 makes constructive interference
Diffraction Grating Equation
dsinθ=nλ
d= split seperation
λ= wavelength
n= number of lines
Hubble Discoveries
> Distant galaxies had the same spectrum but each line was longer wavelength.
The Doppler Effect
> Apparent change in wavelength due to the relative motion between a source and an observer
red shift away
blue shift towards
Evolution of the universe
> 0-1ms: high energy photons
produce quarks and leptons
from pair production
1ms-100s:Quarks combine to
form hadrons. Universe also
contains leptons
100s-380,000years- protons and
neutrons fuse to form simple
nuclei mainly helium.
From 380,000 years- Atoms can
form from nuclei and electrons.
photons no longer have enough
energy to ionise and are free to
travel through a transparent
universe and become CMBR
over time less dense less hot
Hubbles Law
> The speed of recession of distance galaxies is directly proportional to their distance away
The Doppler Formula
> 𝚫λ/λ=𝚫f/f=v/c
𝚫λ= observed λ-λ
v= speed of galaxy
c= speed of light
Hubbles Constant
> H=v/d=ms^-1/m=s^-1
gradient of graph = h = hubbles constant
Big Bang Theory
> expanding universe
age can be measured
Composition of the universe
> 5% ordinary matter
25% dark matter
70% dark energy
Cosmological Principal
> on a large scale universe is homogenous and isotropic
homogenous: universe has
uniform density on the large
scale
isotropic:universe looks the
same in all directions
Cosmic Microwave Background Radiation
> virtually uniform in all directions
temperature of 2.7K
is photons from the big bang
who’s wavelength is stretching
tiny variation are tiny variations that led to galaxies and stars formation
