1.6 Flashcards
What is the doppler effect?
the shift in frequency of a wave produced by a moving object with respect to an observer.
Break down the equation
fo = fs (v/v+_ vs)
fo = frequency observed (Hz)
fs = frequency of source (Hz)
v = velocity of wave (ms^-1)
vs = velocity of source (ms^-1)
Why is the denominator ‘plus or minus’ and when do you use each of them?
The Doppler effect applies for both objects moving away and towards an observer.
When the object is moving towards the observer, the ‘-‘ is used.
When the object is moving away from the observer, the ‘+’ is used.
What is redshift?
The shift in wavelengths of light as observed from distant galaxies from Earth. This shift indicates that these galaxies are moving away from Earth.
What is blueshift?
the observed wavelength of a light source is shifted towards the blue end of the spectrum as the light source moves towards us.
Why can’t the Doppler equation be used to calculate redshift?
Galaxies are moving away at such high speeds that relativistic effects need to be considered.
Break down the equation
z = ~observed - ~rest/~rest
z = redshift (no units)
~observed = observed wavelength (m)
~rest = rest wavelength (m)
Break down the equation
z = v/c
z = redshift (no units)
v = velocity of object (ms^-1)
c = speed of light (ms^-1)
What is Hubble’s Law?
the redshift witnessed from distant galaxies, and thus their speed of recession, is directly proportional to their distance. Hence, the further away a galaxy is, the faster it is moving away.
Break down the equation v = Ho x d
v = recessional velocity (ms^-1)
Ho = Hubble’s constant (2.3 x 10^-18s^-1)
d = distance (m)
What important value does Hubble’s Law allow us to estimate?
The age of the universe
What is the significance of Hubble’s Law when discussing the expansion of the universe?
we know that further galaxies are moving away at a larger velocity than those closer to Earth. This implies that the space between objects in space is expanding.
How can the mass of the galaxy be estimated?
using the oribital speed of the stars around the central point of the galaxy.
What is dark matter?
When scientists observed the mass of galaxies and their rotational velocities, there was not enough mass to account for the gravitation attraction force required. Dark matter accounts for this ‘missing’ mass.
What is dark energy?
When scientists accounted the true mass of galaxies, the gravitational attraction was too large for galaxies to be expanding. We know this to be untrue, so dark energy allows galaxies to overcome this atttraction force and expand.
