Module 5 - 5.5.3 Cosmology Flashcards
The Astronomical Unit (definition)
The mean distance from the centre of the Earth to the centre of the Sun
1AU = 1.5x10^11m
The Light Year (definition)
The distance travelled by light in one year
1 degree = – arcminutes
60
The Parsec (definition)
A unit of distance that gives a parallax angle of 1 second of an arc using the radius of the Earth’s orbit (1AU) as the baseline of a right-angled triangle
for small angles, tan(p) =
p
Stellar Parallax (definition)
The apparent shifting in a position of a star viewed against a background of distant stars when viewed from different positions of the Earth, such as at different positions of the Earth’s orbit
Stellar parallax can be used to measure (2)
- the distance to nearby stars
- involves observing how the position of a nearby star changes over a period of time against a fixed background of stars
A nearby star will have a — parallax angle
larger
The Doppler Effect (definition)
The apparent shift in wavelength/frequency caused by the relative motion between a wave source and an observer
The Doppler Effect: wavelength if the wave source is moving
- towards an observer
- away from an observer
- shorter
- longer
Red Shift (definition)
The apparent increase in wavelength of em radiation caused when the source is moving away, relative to an observer
The Doppler Effect in stars (4)
- compare the light spectrum produced from the Sun with that of a distant galaxy
- the pattern of lines is shifter towards the red end of the spectrum for stars travelling away from us
- known as red shift
- this is evidence that distant galaxies are moving away from us
Red Shift is more pronounced for (2)
- galaxies that are further away
- Hubble concluded that galaxies which are further away from Earth are moving faster than galaxies which are closer
Hubble’s Law
The recessional velocity of a galaxy is proportional to its distance from Earth
Recessional Velocity (definition)
The velocity of an object moving away from an observer
Estimating the Age of the Universe, use
t = 1/H0
Olber’s Paradox (definition)
An argument in astrophysics that says the darkness of the night sky conflicts with the assumption of an infinite and eternal static universe
Cosmic Background Radiation (definition)
Microwave radiation received from all over the sky originating from the early stages of the universe after the Big Bang
Astronomers found that Microwave Background Radiation has a peak wavelength corresponding to a temperature of
2.7K
Microwave Background Radiation has (2)
- the exact profile expected to be emitted from a hot body that has cooled down over a very long time
- is uniform
Origins of Microwave Background Radiation (4)
- according to the Big Bang Theory, in the early stages of the Universe, matter and antimatter annihilated
- this produced lots of gamma photons (em radiation)
- this radiation has expanded with the expansion of the Universe
- is now in the microwave region of the EM spectrum
The Big Bang Theory (definition) (3)
- the universe was created from a hot singularity which was infinitely dense, hot and small where all of the Universe’s current mass was situated
- there was a giant explosion known as the Big Bang
- time and space were created at this instant
Steady State Theory (definition)
The Universe was static and had always existed and that matter was continually being generated from nothing to account for the expansion of the Universe
General Relativity (definition)
Space and time are connected together a space-time, a property that connects the three dimensions of space and a fourth dimension of time
Outcomes for the Future of the Universe: Density is too high (3)
- closed universe
- density so high that gravitational forces will prevent galaxies going on out into space forever
- instead they will slow down, stop and eventually collapse in on itself in the Big Crunch
Outcomes for the Future of the Universe: Density is too low (3)
- open universe
- each galaxy will reach a constant velocity when sufficiently far apart from one another for the gravitational force on each to be negligible
- galaxies will continue to separate forever, cooling down as they do
Outcomes for the Future of the Universe: Density if exactly the critical density (4)
- flat universe
- universe will expand, decreasing in velocity as it does
- it will eventually reach a final finite size after an infinite amount of time
- meaning galaxies will gradually slow down but never stop
Dark Matter (definition)
Matter which cannot be seen and that does not emit or absorb electromagnetic radiation
(scientists know it exists, but don’t know where it came from)
Detection of Dark Matter (2)
- cannot be detected directly through telescopes
- detected indirectly based on its gravitational effects relating to other galaxies
Dark Energy (definition)
A type of energy that permeates the whole universe and opposes the attractive force of gravitation between galaxies via the exertion of a negative pressure
Detection of Dark Energy
cannot be detected easily
