Chapter 20 Cosmology (The big bang) Flashcards
What is an astronomical unit? What is its distance?
It is the average distance between the earth and the sun.
It is 1.5x10^11m
What is a light year? How far is it?
It is the distance that light travels in a vacuum in a time of 1 year
9.46x10^15m
What is an arcminute? How many arcminutes are there in 1º?
An arcminute is a way of splitting up 1º into smaller parts which is usefull when measuring long distances. There are 60 arcminutes in 1º
How many arcseconds are there in 1 arcminute?
60
How many arcseconds are there in 1º?
3600
How is a parsec defined?
It is defined as the distance at which a radius of 1 AU subtends an angle of one arcsecond.
or in simpler terms
It is the distance produced from the sun to a point when the angle between the point and the sun and the point and the earth is 1 arcsecond
What is the distance of a parsec in metres?
3.1x10^16m
What will the angle between the earth and a point and the sun and a point if the point is 3 parsecs away?
It will be 1/3 arcseconds
What is stellar parallax?
It is a technique used to determine the distance to stars that are relatively close to the earth. Less than 100pc distance
What is parallax?
It is the apparent shift in the position of a relatively close star against the backdrop of much more distant stars as the earth orbits the sun
How does stellar parallax work?
A close star is viewed from earth against the background of other stars.
Then 6 months later as the earth is on the opposite side of the sun, the star is then viewed again against the background of other stars.
If the parallax angle (the angle between the star and the sun and the star and the earth) is calculated in arcsecondsthen this can be used to work out the distance of the star from the sun.
What is the equation for stellar parallax?
d = 1 / p d = distance p = parallax angle in arcseconds
Why is stellar parallax limited to close stars?
As the star gets further away the parallax angle is harder to calculate accurately so an inaccurate distance would be calculated
What is doppler shift?
As a wave source moves relative to an outside observer, the frequency and wavelength of the waves received by the observer change based off the speed of the moving wave source
Explain doppler shift using a F1 car as an example?
As an F1 car moves towards a stationary observer, the sound waves get bunched up in front of the car producing a higher pitched sound.
As an F1 car moves away from a stationary observer the sound waves get spread out behind the car and produces a lower pitched sound.
This is why F1 cars make the “Neeeee-awwwwwwwww” sound
What sort of waves does the doppler shift apply to?
It applies to all types of waves
How can the doppler shift be used?
It can be used to work out the speed of moving objects
What is blue / red shift and where does it occur?
As galaxies move towards or away from the earth the light that they produce will be doppler shifted.
If a galaxy is moving towards the earth the light will be shifted towards the blue end of the spectrum (aka blue shifted)
If a galaxy is moving away from the earth then the light will be shifted towards the red end of the spectrum (aka red shifted)
What is the doppler equation?
Δλ / λ = Δf / f = v / c
The faster a wave source moves…
The greater the doppler shift