ODU, The Expanding Universe Flashcards
What is the Doppler effect?
The change in frequency observed when a source of sound waves is moving relative to an observer.
What is the redshift of a galaxy?
The change in wavelength divided by the emitted wavelength. For slow moving galaxies, it is also the ratio of the recessional velocity of the galaxy to the velocity of light.
What does the Doppler Effect cause?
Shifts in wavelength of sound and light.
How is the light from objects moving away from us shifted?
It is shifted towards longer wavelengths (redshift).
What does Hubble’s law allow us to estimate?
Hubble’s law allows us to estimate the age of the universe.
What lead to the theory of the expanding universe?
Measurements of the velocities of galaxies and their distance from us.
How can the mass of a galaxy be estimated?
By the orbital speed of the stars within it (mass of galaxy is directly proportional to orbital speed of stars within it).
What evidence is there for the existence of dark matter?
Estimations of the mass of galaxies suggest there is more matter than astronomers can detect.
What evidence is there for the existence of dark energy?
The accelerating rate of expansion of the universe tells us there must be something overcoming the force of gravity.
Temperature of stellar objects.
Temperature of stellar objects is related to the distribution of emitted radiation over a wide rage of wavelengths.
Peak wavelengths of this distribution is shorter for hotter objects than for cooler objects.
Hotter objects emit more radiation per unit surface area per unit time than cooler objects.
What evidence is there for the Big Bang theory and the subsequent expansion of the universe?
Cosmic microwave background radiation (CMBR) is uniformly distributed across the universe; the abundance of the elements hydrogen and helium; the darkness of the sky (Olber’s paradox); and the large number of galaxies showing redshift rather than blueshift.
