Cosmology Flashcards
State Hubble’s law
Recessional speed / velocity of galaxy is proportional to its distance (from us)
State how an emission line is produced.
Electron(s) makes a transition to a lower (energy) level / loses energy and emitting a photon(s) / EM radiation
Suggest why hydrogen spectral lines play an important role in determining red shift of
galaxies.
Hydrogen is abundant.
Explain why high temperatures are necessary for fusion reactions to occur in stars.
The protons / nuclei repel each other
At high temperature) particles have more KE and hence can get close (enough to fuse
What is an astronomical unit (AU)?
The average distance between the Earth and the Sun. 1AU = 1.50x10^11m
What is a parsec (pc)?
The distance at which one astronomical unit (AU) subtends an angle of one arcsecond.
What is the Doppler Effect?
The change in frequency or wavelength when there is relative velocity between the source and the observer.
What is blue-shift?
The source of light is moving towards Earth, causing the entire spectrum observed from the source to be shifted to shorter wavelengths.
What Is red-shift?
The source of light is receding away from Earth, causing the entire spectrum observed from the source to be shifted to longer wavelengths.
What is the cosmological principle?
When viewed on a large enough scale, the Universe is homogeneous and isotropic, and the laws of physics are universal.
What is Olber’s Paradox?
For an infinite and uniform universe, the sky at night should be light not dark.
What is the critical density?
The density of the universe that will give rise to a flat spacetime.
