| what is the doppler effect | the change in frequency observed when a source of sound (or light) waves moves relative to an observer |
| what happens to sound frequency when a source is moving towards the observer | it increases |
| what is the formula for doppler effect | where fo is observed frequency in hz
fs is source frequency in Hz
v is speed of sound waves in ms-1
vs is speed of source in ms-1
(the sign in the denominator is negative if source is moving towards the observer and positive when source is moving away from the observer) |
| what happens to frequency of sound source moving away from an observer | it decreases |
| what is redshift | an example of the doppler effect in which light from stars or galaxies that are moving away from us is shifted to longer wavelengths |
| what is blueshift | when light from stars or galaxies moving towards us is shifted to shorter wavelengths |
| what is the formula for redshift when given wavelengths | where z is red shift (no unit)
lambda observed is the observed wavelength of light from the star in metres
lambda rest is the wavelength of light emitted by the star measured in metres |
| what is a negative red shift equivalent to | a blue shift |
| what is the formula for redshift for galaxies moving at non-relativistic speeds (less than ten percent of the speed of light) | z=v/c
where z is red shift
v is the recessional velocity of the galaxy in ms-1
c is the speed of light in metres per second |
| what is hubbles law | the further away a galaxy is, the faster it is moving away from us (the higher its recessional velocity)
this suggests that the universe is expanding |
| what is the formula for hubbles law | v=H₀d
where v is the recessional velocity of the galaxy in ms-1
Ho is hubbles constant in per seconds (s-1)
d is the distance to the galaxy in metres |
| how do you calculate the age of the universe using hubble's constant | t=1/Ho |
| how much is 1 light year in meters | 9.46x10^15 m |
| describe the movement of galaxies | galaxies rotate around their cores
stars within the galaxy rotate with varying orbital speeds
stars on the outer arms of a galaxy should travel slower than those closer to the galactic core as they are further from the centre of the mass and therefore experience a smaller gravitational force of attraction |
| how can the mass of a galaxy be estimated | from the orbital speed of the stars within in
this is done by measuring the red shift and blueshift of the light coming from the stars |
| what is unusual about the orbital speed of stars within galaxies? | stars in the outer parts of galaxies are moving far faster than they should for the mass that is visible to us
for the mass we can observe, the stars should escape the gravitational pull of the galaxy and fly into space, but something is preventing them from doing so
astronomers concluded that there must be a considerable amount of matter in galaxies that we cannot see, called dark matter |
| what do recent observations of the redshift of distant galaxies show is happening to the rate of expansion of the universe | it is increasing |
| what evidence is there that there is an unknown force acting against gravitational attraction? | the rate of expansion of the universe is increasing which contradicts the idea that gravity should be an unbalanced force acting to slow down this expansion
this source of energy capable of producing this force has not yet been determined and is simply called dark energy |
| what was the big bang | a rapid expansion of the universe from a singularity
our universe is thought to have begun as an infinitesimally small infinitely hot infinitely dense singularity
after its initial appearance the universe inflated , expanded and cooled, going from very small and very hot to the size and temperature of our current universe
it continues to expand and cool to this day |
| what does the colour of a star tell us | the surface temperature of that star with red being the coolest and blue being the hottest |
| what type of radiation do stars emit | electromagnetic radiation over a wide range of wavelengths |
| what information can we see from a intensity of emitted radiation/wavelength graph for stellar objects | graph has a blackbody curve
stellar objects emit radiation over the complete electromagnetic spectrum
each stellar object has a peak wavelength that depends on its temperature |
| what is the relationship between the temperature of a star and the radiation emitted | as star temperature increases there is more radiation emitted per unit surface area per unit time area under curve on graph increases as star temperature decreases the peak wavelength shifts to a shorter wavelengths |
| how does redshift and hubbles law provide evidence for the big bang | hubbles law suggested that galaxies are moving away from us and each other and therefore the universe is expanding
light from these distant galaxies would become more stretched out which mean light would shift towards red
if we were to go back in time there must have been a moment where the universe was a single point |
| how does cosmic microwave background radiation provide evidence for the big bang | background radiation comes from all directions in space
originally this radiation was at a much shorter wavelength but the expansion of the universe caused the wavelengths to increase over time, and the peak wavelength is now in the microwave part of the spectrum |
| how does the temperature of the univeerse provide evidence for the expansion of the universe | as the universe expanded it also cooled down and now has a temperature of 2.7K (almost absolute 0) |
| how does the relative abundance of hydrogen and helium provide evidence for the expansion of the universe | although the big bang produced helium and lithium, all elements heavier than lithium can only be made by thermonuclear reactions in stars
the relative proportions of the elements that we observe today, helium, hydrogen, and other light elements, correspond to what is predicted if the universe started around 14 billion years ago. |
| light coming from galaxies is red shifted. explain why this gives evidence of the big bang | red shift is evidence that the universe is expanding
expanding universe is evidence that supports the big bang theory |
