Last ditch

Question 1

What are the two reasons that a reflecting telescope with a mirror of 2m in diameter is preferable to one with a 1m diameter mirror

Answer 1

1. Smaller diffraction limit, allows objects with smaller angular separation to be clearly resolved
2. More light gathering capability

Question 2

What is the most important reason that the Chandra X-ray observatory is located in space, as opposed to being on Earht

Answer 2

X-rays are mainly abosorbed by the Earth’s atmosphere

Question 3

Describe some of the evidence that there is a supermassive black hole at the center of the milky way

Answer 3

• Orbits of stars near galactic center (K’s 3rd law to get a very large mass)
• Direct radio imaging of event horizon with event horizon telescope

Question 4

what is a standard candle

Answer 4

Distant source of light with known luminosity. Use that to get apparent brightness and inverse law to get distance

Question 5

Why are type Ia supernova a good standard candle

Answer 5

Type Ia supernova have the same luminosity since they all come from the explosion of WD once they reach Chandrasekhar limit. Also so bright they can be seen in distant galaxies

Question 6

Why are there many more white dwarfs than planetary nebulae

Answer 6

Planetary nebulae dissipate rapidly while WDs live very long

Question 7

What is a red dwarf

Answer 7

Smallest star on the main sequence

Question 8

What is needed to change with the moon in order to change the tides on Earth

Answer 8

Mass and distance

Question 9

What experimental evidence caused scientists to abandon the steady state theory

Answer 9

Discovery of the cosmic microwave background radiation

Question 10

What observations make us believe that the universe is filled with dark energy

Answer 10

Observations of distant supernovae show that the universe is accelerating its rate of expansion

Question 11

How do we know that much of the light from a quasar comes from an extremely small volume

Answer 11

Fluctuates on a time scale of days, so it must be smaller than light-days, which is very small compared to a galaxy

Question 12

Rank the following from smallest to biggest:
- neutron star
- red giant
- sun
- solar system
- singularity of a black hole
- white dwarf

Answer 12

singularity (zero size), neutron star, WD, sun, red giant, solar system

Question 13

Rank the following in order of decreasing contribution to total energy content of the universe
- H
- He
- elements not H and He
- Dark energy
- dark matter

Answer 13

Dark energy, dark matter, H, He, elements other than H and He

Question 14

Put the following in chronological order
-formation of first stars
- cosmis “dark age”
- formation of atoms
- formation of nuclei
- inflation
- formation of protons and neutrons

Answer 14

inflation, formation of neutrons and protons, formation of nuclei, formation of atoms, dark ages, first stars

Question 15

What are the three types of galaxies and which type is the milky way

Answer 15

spiral, elliptical, and irregular. Milky way is spiral

Question 16

What was discovered via radio telescope to be a new kind of celestial object and what are they

Answer 16

Pulsars, rapidly rotating neutron stars

Question 17

How does galactic rotation provide evidence for dark matter

Answer 17

Galactic rotation curves are plots of rotational velocity vs distance from center of galaxy. If one uses just the visible mass, can predict the amt of mass at smaller radius, and thus this in Kepler’s 3rd law to calculate what rotational speed should be. For most galaxies this fails, proving there is more mass than is visible in the galaxy, and that this mass extend to much large radii than does the visible mass: dark matter

Question 18

Look at picture in study guide. What is it? what do the spots represent? Explain relevance to clusters and superclusters of galaxies

Answer 18

Temperature of the CMB. Diff colored spots are slightly hotter and colder regions. Spots will gradually grow and turn into clusters or superclusters of galaxies

Question 19

what are the three scenarios for the future of the universe

Answer 19

1. collapsing: big crunch
2. flat: right amount of matter to balance
3. open: expanding universe

Question 20

what is critical density

Answer 20

Overall density needed to “win” against gravity. faster expanding universe = more density needed

Question 21

What are Quasars and what is their importance

Answer 21

“Quasi-stellar radio source” that are found to be located at the same spot in the sky. Are incredibly red-shifted that they must be receding at a huge speed. So bright that they give us a window into galaxies in the early universe

Question 22

What is the Tully-Fisher Law

Answer 22

Luminosity depends on the rotational rate. Spiral galaxies with higher rotational velocities tend to be more luminous.

Question 23

What are the two broad classes of stars and how do they differ

Answer 23

Population I stars
- in the disk, orbiting the galactic center
- typically young open clusters
- composed largely of heavy elements (composed of the remnants of other stars)
Population II stars
- mainly in the halo, follow elliptical orbits
- typically very old (11 - 13 billions years)
- Almost entirely H or He

Question 24

What is gravitational lensing

Answer 24

When there is a large object between you and a light source, the light will be bent so that you can see it in two places. Can sometimes result in an “Einstein ring” around the object