PHYS 190 Study Guide - Final Guide: Solar Mass, Main Sequence, Big Bang
10 May 2018
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Short Question for Final:
1. Why does the Moon sometimes glow coppery red during a total lunar eclipse?
- during totality, earth appears as a dark disk surrounded by a red ring because of the light from the planet's sunsets and sunrises
2. Draw the orbit of a planet in the Geocentric model, and identify the Earth, the planet, and the planet's deferent and epicycle.
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3. What two forces are balanced in the gravitational equilibrium of a star? What causes a star to go out of equilibrium near the end of its life?
- inward pull of gravity and outward push of internal gas pressure. gravity b/c it tries to get the star's core to collapse
4. Why is there is a lower-limit to the mass of main sequence stars?
- because the stars that are below 0.08 solar mass that are never hot enough for hydrogen burning to begin. Their luminosity is because of the burning of
deuterium, however this energy is rapidly exhausted
5. What are black dwarfs, and why haven't any been formed yet?
- a black dwarf is a white dwarf that stops emitting light and heat
b/c the universe is still young
6. Why do hot blue main-sequence stars live far shorter lives than red dwarf stars, even though they have much larger masses?
- because with larger masses, they have more material to burn through faster due to the cores temperature
7. Why do astronomers say that black holes don't "suck"?
- b/c black holes have a mass and exert gravitational force on their surroundings, however, black holes are the only objects with their event
horizon outside their physical boundary, so when you get near to it,strange physical effects occur b/c of the strong gravitational field associated
with these objects
8. List the top four pieces of evidence that support the Big Bang Theory, as identified in our class lectures. Pick one of them and describe how it supports the
theory.
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1. hubble's expansion
2. cosmic microwave background
3. big bang nucleosynthesis
4. large- scale structure
CMB supports big bang theory bc of the Microwave radiation temperature, and how our universe is almost perfectly uniform everywhere on the
sky. The universe itself is a blackbody b/c we are surrounded by the left over radiation from the BB. some ripples "had" to be there, since a
perfectly uniform early universe could not have evolved to galaxies, stars, and us
9. Why is the cosmic background radiation visible in all directions?
- Because after the big bang the radiation from the event is surrounding us. earlier, the very hot radiation was red shifted to much cooler temperatures
10. Describe a piece of observational evidence that suggests that most of the matter in the universe is in the form of dark matter
- amount of matter in the universe determines its destiny,
there were 3 cases to determine where most of the matter came from: to little mass, not quite enough mass and enough mass. but in 1998 expansion was
speeding up and found that 30% of dark matter would be able to stop this expansion
11. In what way is dark energy affecting the expansion of the universe?
- through Einsteins theory of gravity, the simplest possibility for D.E is a "repulsive energy of empty space". However, the cosmological constant suggests that
this empty space can possess energy. As a result, this form of energy would cause the universe to expand faster and faster.
12. Olbers’ paradox states that the sky would be blazing with light if the universe is infinite in size (so that everywhere we look we would see a star), and
infinitely old. Suppose that the universe was infinite in size, but had a finite age. Why wouldn’t the sky be blazing with light?
- the light from distant galaxies and stars are redshifted, making them seem cooler than they actually are, so the night sky is dark b/c universe is expanding
and has a finite age
