Astronomy and Cosmology:
Q. What is meant by the term luminosity?
Luminosity is an absolute measure of the total power of the
electromagnetic radiation emitted by a star.
Q. Define the mathematical relationship between flux
intensity and luminosity?
F = L/ 4πd2
Where F is the flux intensity, L is the luminosity, and d is
the distance between the radiation source to the receiver.
Q. What is meant by the term standard candle?
A standard candle is an object of known luminosity.
Q. Give a common astrological use of standard candles?
Standard candles are often used in order to determine the
distance to far-off galaxies.
Q. What is a blackbody?
A blackbody is a perfect emitter and absorber of all
possible wavelengths within the EM spectrum. Stars can be modelled as
blackbodies.
Q. State Wien’s displacement law.
Wien’s displacement law states that the blackbody radiation
curve, for bodies of different temperatures, will peak at different radiation
wavelengths such that the wavelength at the peak radiation is inversely
proportional to the source body surface temperature.
Q. State Wien’s displacement law mathematically.
Lambda peak = b / T
Where b is Wien’s displacement constant = 2.898 x 10-3
mK, lambda peak is the radiation wavelength at the peak radiation intensity,
and T is the surface temperature of the source body.
Q. Give an equation that defines the Stefan-Bolzmann law.
L = 4πσr2T4
Where L is the radiating body’s luminosity, σ is the
constant of proportionality = 5.67 x 10-8 Wm-2K-4,
r is the radius of the body, and T is its surface temperature.
Q. What is redshift?
Redshift is the phenomenon resulting from an increase in
wavelength of EM radiation (light) emitted by an object that is moving away.
Light is instead blueshifted (shortened wavelength) if the object is moving
from the observer.
Q. The vast majority of galaxies have higher observed
wavelengths in their observed emission spectra than the known wavelength
values. Can you explain why this might be?
The EM radiation emitted by these galaxies has been
redshifted. This suggests that many more galaxies are moving away from the
Earth than moving towards, which provides evidence that the universe is
expanding and in favour of the Big Bang Theory.
Q. State Hubble’s Law.
V = Ho d
Where v is the velocity with which a stellar body is moving
away from the Earth, Ho is Hubble’s constant and d is the distance of the body
from Earth.
Q. Why does Hubble’s law suggest the universe is
expanding?
Hubble’s law draws a direct proportional relationship
between the distance of stellar bodies from Earth and the velocity at which
they are travelling away from Earth. This implies that stellar objects are
moving away from one another as well as away from Earth, suggesting that the
universe is expanding.
Q. Why does Hubble’s law give evidence to support the Big
Bang theory?
Instead of using Hubble’s law to forecast the expansion of
the universe, we can use it to extrapolate back in time. If we go back in time,
the universe will decrease in size, according to Hubble’s law. If we
extrapolate things back far enough, all mass can be considered to originate
from a single point. The origin of the universe from such a singularity is the
essence of the Big Bang Theory.
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