Chapter 20: Cosmology Flashcards
What is the Doppler Effect?
The change in wavelength and frequency of a wave as a source moves away from or towards the observer
What is Stellar parallax?
The apparent shift in position of an object against a backdrop of distant objects due to the orbit of the Earth
Used to calculate distances of up to 100pc
Parsec
The distance from which 1 AU (distance between the Earth and Sun) subtends an angle of 1 arcsecond (1/3600th of a degree)
Cosmological Principle
Universe is isotropic and homogeneous and the laws of physics are universal
Isotropic
universe is the same in all direction to every observer, no centre of edge
Homogenous
Matter is uniformly distributed - for a large volume of the Universe the density is the same
Red shift
Shift in wavelength and frequency of waves from a retreating source towards/ beyond the red end of the electromagnetic spectrum
Evidence of the Big Bang
Hubble’s Law
The velocity of receding objects is directly proportional to their distance from Earth
What is the Big Bang theory?
13.8 Billion years ago, the universe exploded from an extremely hot and dense point and is still expanding now
What is the evidence for the Big Bang theory?
CMBR is the heat signature left behind from the Big Bang.
EM radiation is released in the explosion shifted from extremely high energy waves into the microwave region as the Universe expanded, stretching out the waves.
CMBR has a black body distribution with a peak that corresponds to a temperature of 2..7K
There was nuclear fusion of hydrogen into helium which explains the large abundance of helium in today’s universe.
What is dark energy?
- When astronomers calculated the distance to some Type 1A supernova, they discovered them to be dimmer than expected. This suggested the expansion of the universe is accelerating, which is attributed to dark energy.
- Dark energy is thought to be energy that has an overall repulsive effect throughout the Universe.
light year
Distance travelled by light in a vacuum in a time of one year
What happened microseconds after the Big Bang?
first fundamental particles gain mass
What happens milliseconds after the Big Bang?
Most of the mass is created using pair production. First hadrons come from quarks
What happens seconds after the Big Bang?
Production of mass is halted
What happens 100s after the Big Bang?
Protons and neutrons fuse to form deuterium, helium, lithium and beryllium but nothing heavier.
Rapid expansion continues.
25% of matter is helium nuclei
What happens 380 thousand years after the Big Bang?
Now cool enough for first atoms to form
What happens 30 million years after the Big Bang?
First stars form, fusion creates heavier elements
What happens 200 million years after the Big Bang?
Milky way forms, as gravitational forces pull clouds of hydrogen and existing stars together
What happens 9 billion years after the Big Bang?
Solar system forms by a nebula from a supernova. This is followed by the formation of our Sun
What happens 11 billion years after the Big Bang?
Primitive life begins on Earth
What happens 13.7 billion years after the Big Bang?
first modern humans evolve
How do you make an emission line spectra?
- heat gas to a high temperature so electrons excite
- as gas cools electrons move down to lower energy level and release photon
- photons cause coloured lines on black spectrum
How do you produce an absorption line spectra?
- white light is shone through cool gas
- low temperatures mean most electrons are at ground state
- some absorb photons, leading to missing wavelengths in spectrum
