Download Review 1 Solutions

AY C10 / L&S C70U Fall 2006
Nicholas McConnell
Matching
1. This is an intrinsic property of a star
that depends on its temperature and radius.
C
A. Black Hole
B. Brightness
2. This is an observed property that
depends on a star’s temperature, radius,
and distance. B
C. Luminosity
D. Spiral Galaxies
3. This is an angular method of
determining distances for nearby objects.
H
E. Elliptical Galaxies
F. Globular Clusters
4. This is a term for a bright object with
very high redshift. G
5. These galaxies are usually old and are
prevalent in galaxy clusters. E
G. QSO
H. Parallax
I. Cepheid Variable Stars
1. Nothing can escape a black hole within
this distance. E
A. Type Ia Supernova
2. This is the region in which work must
be extracted from a rotating black hole.
F
B. Type II Supernova
3. This supports white dwarfs, brown
dwarfs, and neutron stars from selfcollapse.
D
D. Degeneracy Pressure
4. This can occur when a giant star
accretes mass onto a white dwarf. A
F. Ergosphere
C. Gravity Pressure
E. Schwarzschild Radius
G. Dark Matter
5. This describes the relationship between
galaxies’ distances and their apparent
radial speeds, which occur as a result of
the universe’s expansion.
I
H. Dark Energy
I. Hubble’s Law
AY C10 / L&S C70U Fall 2006
Nicholas McConnell
True or False
1. The night sky is mostly dark because we can only see stars within about 13.8 billion
light years of us. T
2. The “rotation curves” that plot stars’ orbital speeds versus their distance from their
galaxy’s center initially surprised astronomers by suggesting that large amounts of
invisible matter exist in the galaxies’ outer regions. T
3. Every galaxy in the universe is moving away from the Milky Way. F
4. It is theoretically possible to outlive your peers by traveling near (but not crossing) the
event horizon of a black hole and returning, because in this process you will age more
slowly than everyone on Earth. T
5. Gravitational lensing does not support the theory of dark matter, because we see
galaxy clusters near the line of sight to gravitationally lensed objects. F
6. A quasar with a redshift of one (z = 1) is receding from us at the speed of light. F
7. Cepheid variable stars and Type Ia supernovae are examples of “standard candles”
which have a known luminosity and thereby allow astronomers to determine precise
distances to galaxies outside our own. T
8. Quasars are thought to come from super-massive black holes accreting matter because
they produce large amounts of energy throughout a volume thousands of parsecs across.
F
9. At the largest observable scales, the universe appears the same in all directions. This
is a result of the Milky Way’s special position at the center of the universe. F
10. Neutron stars can be more massive than white dwarfs because neutron degeneracy
pressure is stronger than electron degeneracy pressure. TShort Answer
AY C10 / L&S C70U Fall 2006
Nicholas McConnell
1. A transparent sphere 1 parsec in diameter glows for a split second over its entire
surface. How long (approximately) does the glow last for an observer outside the
sphere?
One parsec is equal to about 3 light years. Once the light from the front of the sphere
reaches us, it will take about 3 years before the light from the back does.
2. What is a WIMP?
A WIMP is a Weakly Interacting Massive Particle. According to the leading current
theory, dark matter is composed primarily of WIMPs, which cannot be detected by
ordinary means.
3. Which of the following are presently expanding? Circle all that apply.
Earth
Solar System
Milky Way
Galaxy Cluster
Cosmic Void
Universe
Cosmic voids are presently expanding, as is the universe as a whole.
A Blast from the Past (more short answer)
4. What are three stages a 5-solar-mass star goes through after it leaves the main
sequence?
Red giant, planetary nebula, white dwarf
5. What quantities go on the horizontal and vertical axes of the H-R diagram?
Horizontal: Temperature (spectral type or color are also all right; both correspond to
temperature)
Vertical: Luminosity
6. You crack open a glowstick and throw it into a nearby black hole. What are two
things you observe as it approaches the event horizon?
Light from the glowstick will be redshifted, eventually passing out of the visible
spectrum. Also, the glowstick will appear to slow down as it approaches the event
horizon, eventually coming to a complete stop from our point of view.
AY C10 / L&S C70U Fall 2006
Nicholas McConnell
7. Jupiter’s moon Callisto has lots and lots of craters, whereas another moon, Io, has
almost none. What does this tell us about Io and Callisto?
Io has a younger surface than Callisto. From other observations, we know this is because
of volcanic activity on Io that constantly replenishes its surface with lava.
8. During what lunar phases are tides on Earth the most exaggerated?
Tides are exaggerated during full moon and new moon, when the sun and moon stretch
the Earth along the same direction.
9. What is spherical aberration, and how is it corrected?
Spherical aberration is a problem in reflecting telescopes that use spherical mirrors—light
does not reflect to a single focus point for this shape. It can be corrected by using
parabolic mirrors instead of spherical ones.
10. Why do stars twinkle?
Stars appear to twinkle from the ground because Earth’s atmosphere subtly bends the
starlight (this is due to refraction; it is not a gravitational effect) in different directions.
The star appears brighter when the light is temporarily focused toward us and dimmer
when it is focused elsewhere.
11. Suppose moon Angel orbits planet Buffy with a known period and semi-major axis.
Which law do we use to determine Buffy’s mass, and what approximation must we
make?
Kepler’s third law: P2 = 42 / G(M+m) * R3
We must approximate MBuffy >> mAngel, so measuring P and R tells us MBuffy
12. How long is the Sun’s magnetic cycle, and how many activity/sunspot maxima does
it contain?
The Sun’s magnetic cycle is 22 years long—there are two activity/sunspot maxima (and
two minima) in each magnetic cycle.
13. What causes emission lines?
Emission lines are caused by electrons de-exciting (jumping from a high energy level to a
lower one). They can originally become excited through absorption or by heating up.
14. What is the moon’s phase during a solar eclipse?
AY C10 / L&S C70U Fall 2006
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Nicholas McConnell