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
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 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 velocity using
