Cosmology Flashcards
What is an astronomical unit and its value
= 1.5X10^11
The average distance from the earth to the sun
What is a light year
The distance light ravels in a year
Give the conversion for degrees into arc seconds and arc mins
1 degree= 60 arc mins
1 degree= 3600 arc seconds
Definition of a parsec
The distance at which a radius of 1 AU subtends an angle of 1 arc second (1/3600 degrees)
Give an equation using tan to represent a parsec
Tan(1/3600) =1AU/ 1Pc
Therfore
Using small approx tantheata = theata
So
Pc= 1AU/theata
How can we find the distance between a star and a planet
Tan theata (in arc seconds) = Radius (AU)/ distance (pc)
What is parallax
The apparent shift in position of an object against a backdrop of distance objects.
What do the terms mean in the question;
P=1/d
D= distance in parsecs
P= parallax angle in arc seconds
Give a definition for a parsec using the term parallax
An angle of parallax of 1 arc second when the displacement of the earth is 1AU corresponds to a distance of 1 parsec
What is the Doppler effect
When the observer frequency/ wavelength is different to the source frequency/wavelngth when he source moves relative to the observer.
What happens to the wavelength when the source is moving away from the observer in the Doppler effect
If the source is moving towards the observer ten the wavelength appears to decrease if it is moving away then the wavelength appears to increase
However the actual wavelngth of emitted by the source remains the same
State Hubble’s law
The recession speed of a distant galaxy is directly proportional to its distance from earth
Explain the red shift and blue shift
Caused by the source and the observer moving away from eachother therfore wavelngth is longer than when stationary
Blue shift- source and observer moving towards eachother , therfore wavelngths decrease and shift towards blue end of spectrum
Explain the red shift in everyday experiences
When the source of the waves is moving away from an observer therfore each peak of the wave emitted is further away from the previous wave peak
Explain the cosmological red shift
When the whole universe is expanding therfore in the time it takes for the waves to travel between the source and the observer , the space has expanded stretching the wave
What is the equation for Doppler parameter
Z= change in lambda/ original lambda
Why do the most distant galaxies show the greatest red shift
If all galaxies started at the same place at the same time the fastest ones will be the most distant
The light from these galaxies will have been travelling for longer to reach the observer , therfore the universe will have expanded by a grater percentage
( all wavelengths shift by the same percentage difference therfore longer wavelengths shift more)
Derive change in lamda/ lambda= relative velocity/ speed of light in a vacuum
For a stationary source and an observer, the frequency of wave prod. Per second will have travelled a distance of c per second ( 3 x 10^8 m traveled in one second)
Therfore the wavelngth= speed of ight/ frequency
When the source and the observer is moving from eachother at a distance v, the distance covered per second is now c+v
Therfore
Wavelength= c+v / f
Wavelength= (c+v) x 1/f
1/f=wavelngth/ C
Now sub in
\therfore wavelength (obs)= wavelngth/ c x (c+V)
Now expand bracket so that
wavelength(obs)= wavelength c/c + wavelength c/c
C cancels out so now wavelentgh(obs)- wavelength =wavelngthxv/c C cancels
So change in wavelength= wavelength c/c
Therfore
Change in wavelngth/wavelngth= v/c
State how an emission line is produced
When an electron makes a transmission to a lower energy level ( closer to nuclear) ( more negative)
State the cosmological principle
The universe is isotropic and homogeneous and the laws of physics are universal
Isotropic means it appears the same in all directions
Homogeneous means it has constant matter density
State an adjustment that could be made to the red shift effect on spectrum which would space the emission lines more widely
Reduce the grating separation
Give an equation for. The velocity recession using Hubble’s law.
V = H0 x d
Where Hp= bubbles constant
And d = distance
What is the SI unite of hubbles constant
S^-1
What is the units for hubbles law
Kms^-1Mpc^-1
How do we convert kms^-1Mpc^-1 into s^-1
Multiply by 10^3/ 10^6 x pc
How would we calculate the age of the universe?
By doing one divided by Hubble’s constant
Explain the timeline of the Big Bang theory
Time and space are created
At 10^-35s The universe expands rapidly in a period of inflation
10-6 s - The first fundamental particles gain mass
10^-3 s - quarks bind to form hadrons such as protons and neutrons
As the universe is expanding, it is cooling down
After 380,0p00 years
The universe cools down enough for atoms to form
Nuclei and capture these electrons
EM radiation is now detected as the cosmic background radiation
Explain why the cosmic microwave background radiation is evidence to suggest that the universe was founded by The Big Bang Theory
Radiation released as gamma rays stretched into microwave suggesting that the universe is expanding
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Describe the origin of microwave background radiation
During the Big Bang, the universe expanded and as a consequence called down to a temperature of 2.7 Kelvin where gammaray wavelengths expanded and stretched to microwave wavelength
In the middle of the 20th century that were two competing theories for the universe in 1964 electromagnetic radiation was observed coming from all directions in space a graph is given of intensity against wavelength and has the same shape as the black body radiation graph where there is a peak wavelength at 1 mm discuss the main features of this theory of the universe and how the graph provides evidence for one of these theories
Red shift
The theory predicts that distant galaxies are moving away from us the further the galaxy the faster it moves away as the velocity recession is directly proportional to the distance of the distant galaxy from earth
Cosmological microwave background radiation
Siri predicts black body radiation at microwave wavelengths which correspond to a temperature of 2.7 Kelvin from all directions with the same intensity. This indicates that the universe was once a very small ad hot dense state.
The graph shows a peak wavelength in the microwave wavelength which is tend to the -3
And when we do Wayne’s calculation, this wavelength corresponds to the temperature of 2.7 Kelvin which is evidence for CMBR
State what is meant by a standard candle?
It has a known absolute magnitude
Discuss why the evolution of a super giant star in the local part of our galaxy could be dangerous to life on Earth
Will undergo supernova collapse or Star Wars form a neutron star/black hole this produces a gammaray burst which damages DNA
How do you convert from light years to parsec?
First convert light years into meters by multiplying the light years by the value in the data book
Then divide by one parsec
Stay and explain how Stella parallax is used to measure distances in space
Stella parallax is the apparent change in position of a start against a fixed background of distant stars. This is caused by the earths orbit around the Sun.
Measure the parallax angle the radius of the orbit known so we can calculate distance using tan theata
Suggest why hydrogen spectral lines might often be used to measure a stars velocity
Hydrogen is the most abundant element in stars
Light from other elements may be too low in intensity to be detected
The Big Bang theory is an explanation for the stars in the universe. Describe the Big Bang theory as an explanation for the start of the universe and explain the key evidence that supports this theory.
The Big Bang is a theory that suggests all galaxies are receding and the velocity of these receding galaxies is proportional to their distance from earth
CMBR is also evidence for the theory as it says that the universe was formed as gamma radiation at Big Bang which red shifted to microwave wavelength and the intensity of this uniform in all directions this corresponds to a temperature of 2.7 Kelvin
Cyrus a and B are binary stars in our galaxies as Cyrus a is moving towards earth at a relative velocity. There is a percentage change in the wavelength discuss whether Hubble law can be used to find the distance of Sirius a
No, because Hubble’s law is only applied to distant galaxies and not stars
State some properties of the microwave background radiation observed from earth and how it is linked to the Big Bang model of the universe
The intensity of the microwaves is the same in all directions and corresponds to a temperature of 2.7 Kelvin as the universe cooled down so that Gamma radiation emitted during the early stages of the Big Bang stretched due to the red shift and is now detected as microwaves
