Review Questions
Review Questions
These are the questions we'll be answering in this class. For those wondering
if they want to take the introductory astronomy class, these questions can give
you an idea of what the course will cover. For those attending lectures and
reading the text or on-line lecture notes, these questions point you to the
important parts of your reading. For those studying for the exams, being able
to answer these questions (correctly) should ensure a good grade on the exam.
- What is a light year? How would the length of a light year change if we
discovered that the speed of light was two times slower than we previously
thought?
- What is the celestial sphere? What are the reference points: celestial
poles, celestial equator, ecliptic, equinoxes, solstices, zenith, and meridian?
How does their position with respect to the horizon depend on the latitude?
- What is meant by right ascension (R.A.) and declination (dec.)? Why
do astronomers prefer using R.A. and dec.?
- What is a sidereal day? What is a solar day? Which is used for our
clocks? Why is there a difference between the two? Why do we have time zones?
- During a night, how do the stars move? What angle does their nightly
path make with respect to the horizon? How does it depend on latitude?
- How does the sun move with respect to the stars during the year? What
causes the temperature differences between the seasons? How so?
- When will the sun be at its highest altitude in the year in Seattle? How
about Singapore (on the Equator)? Why? When is the sun above the horizon the
shortest amount of time for the Southern Hemisphere? Why? When is the time
of daylight equal to 12 hrs? Does it depend where you are on the Earth? Why or
why not?
- How does the Moon move with respect to the stars? Why does it have
phases? What is happening with the Earth-Moon-Sun positions during an eclipse?
What is a partial eclipse, total eclipse, annular eclipse? Why don't we have
eclipses every month? What causes the tides? How are tides responsible for the
slowing down of the Earth's spin and the Moon's spiralling away from us? What
are spring and neap tides? How are they related to the position of the Moon
and Sun with respect to the Earth?
- What would the Sun-Moon angular separation be for the New Moon if the
``Harvard Hypothesis'' were correct? How about Gibbous phase? What are the actual
angular separations for those phases? About how much delay is there between
the Moon set and Sun set at the 1st quarter phase? Does the Moon set before or
after the Sun at that phase? What will the relative size of the Moon be when
the change in the Sun-Moon angular separation increases? Why is that?
- How do the planets move with respect to the stars? Why are Venus, and
Mercury never seen at midnight while the planets can be visible then? What is
retrograde motion? Are the planet motions random all over the sky or are they
restricted in some way?
-
What two basic models have been proposed to explain the motions of the
planets? What is retrograde motion?
-
What is the Ptolemaic model? What are epicycles? Why are they needed?
Why was the Ptolemaic model accepted for > 1000 years?
-
What is the Copernican model? How did it explain retrograde motion?
Why did Copernicus believe in his model? Did he know the absolute distance
between various planets and the Sun in his model?
-
What is Occam's Razor? How does it relate to the progress of
planet motion theory from Ptolemy to Newton?
-
What important contributions did Tycho Brahe make to astronomy?
-
What important contributions did Galileo make to modern science? What
were his astronomical discoveries? Why was he able to make those discoveries?
Why did he get into political hotwater? What observation finally disproved the
Ptolemaic model?
-
What important discoveries and ideas did Newton make? What basic
fundamental assumption did Newton make about the laws of nature on the Earth
and in space?
-
What is the scientific method? What is a scientific ``model''? What must
the model be able to do to be useful?
-
What 2 things can change for an acceleration?
-
If I give a bowling ball a push FAR away from any gravitational effects,
what will it do? If I throw a feather (again far out in space) at the same
speed as the bowling ball, how will its speed compare to the bowling ball
after 5 minutes?
-
Let's say you're twirling a ball on a string and the string breaks. What
path does the ball take?
-
How does a force exerted on an object relate to the object's mass or
acceleration? Given the same force will a boulder accelerate more than a
regular marble?
-
What are Kepler's three laws? What revolutionary things did his laws
propose for planet motion? Why were they so radical?
-
What shape are orbits? What happens to a planet's orbital speed as it
approaches its farthest point from the sun? As it approaches its closest
point? How is it related to angular momentum?
-
How is the average distance between a planet and the sun related to the
planet's orbit period? Which planet has a shorter period-one with a large
average distance, or one with a small average distance?
-
Do Kepler's laws only apply to our solar system?
-
What are the four fundamental forces of the physical universe? Which have
an effect over only a limited distance? Which have an infinite range of
effectiveness? Why is gravity often the most important force in astronomical
interactions?
-
How do we know that there are probably not any other fundamental forces?
How do we know that the laws of physics on the Earth are the same throughout
the rest of the universe? How do we know that the laws of physics are the
same throughout time?
-
What things does gravity depend on? How does it vary with distance
between objects? With respect to what do we measure the distances?
-
What would happen to the orbit of Io (one of Jupiter's moons) if all of
the H and He in Jupiter were converted to Si and O?
What would happen to the Earth's orbit if the Sun suddenly turned into a black
hole (of same mass)? Why?
-
What would antimatter do in a gravitational field?
-
What is the difference between mass and weight?
-
Does gravity act on an orbiting satellite?
-
What important laws of planet motion can be derived from Newton's law
of gravity?
-
If you are three Earth radii above the Earth's surface, how much would
you weigh?
-
What is the relation between escape velocity and the mass of a planet or star
and the distance from its center?
-
Why is light so very important to astronomy? What kinds of information
can we get from it?
-
What is electromagnetic radiation? Why is it called that?
-
What is a wavelength, frequency, and energy of light? How are they
related to each other? Do all forms of light travel at the same speed in a
vacuum? What is the order of the kinds of EM radiation by energy, wavelength,
and frequency? What is a photon?
-
What forms of light can be observed from the ground (including high
mountains)? What forms can be observed at high altitudes in our atmosphere?
What forms must be observed in space?
-
What are the two basic types of telescopes? What are the advantages of
one type over the other? Of the three powers of the telescope (light-gathering
power, resolving power, magnification) which is more important? Which depend(s)
on the size of the objective mirror or lens?
-
What are the advantages/disadvantages of space telescopes; ground-based
telescopes? What causes stars to ``twinkle'' (scintillate)? What is meant
by seeing?
-
What is a spectrum of light? What does it relate vs. what?
-
What are the three basic kinds of spectrum? Can an object produce more
than one type at the same time?
-
What does a continuous spectrum depend on? What produces it? What's a
blackbody?
-
How can temperature be determined from a continuous spectrum? How would
the color of a hot object compare to the color of a cooler object? At what
wavelength do you at 98.6 degrees Fahrenheit radiate the most?
-
What is the Bohr model of the atom? Where are electrons, protons, and
neutrons located in the atom? How does this model explain emission line or
absorption line spectra? How does it explain continuous spectra?
-
What does an emission line spectrum depend on? What produces it? Do
you need a blackbody source? Can you see emission lines if a blackbody is in
the background? What does their visibility depend on? (Think about the temp. of
the gas producing the emission lines and the temp. of the the background
blackbody.)
-
What does an absorption line spectrum depend on? What produces it? Do you
need a blackbody source? Would you see absorption lines if the gas in front
of a blackbody was hotter than the blackbody? Why must we use a
pattern of lines to find the composition? Why is one line not sufficient?
-
What is the doppler shift? What two things can it tell you about
an object's relative motion? Would a star moving left to right with respect to
you have a doppler shift? Why or why not?
-
What two things determine whether or not a planet keeps an atmosphere?
What things determine the thickness of a planet's atmosphere?
-
What is the relation between the average particle speed and the
temperature and the particle's mass? At a given temperature, which particle
travels the fastest? Which would most likely escape from a planet's atmosphere?
Which would most likely hang around?
-
How are jovian planets different from terrestrial planets?
Why are they different?
-
What distinguishes Venus from the rest of the planets? Why is Venus so
hot?
-
What is the greenhouse effect? What is a runaway greenhouse? Is the
greenhouse problem on Earth different from the ozone problem? How so? How does
the UV-water interaction explain what happened to Venus? How is the same
process prevented on the Earth?
-
What distinguishes Earth from the rest of the planets? What is so
unusual about its atmosphere?
-
What causes the seasons on the planets?
-
If Mars' atmosphere is over 90% carbon dioxide like Venus', why does it
have such a small greenhouse effect? What atmospheric phenomenon can quickly
wipe out any view of its surface from above? Why does Mars have such a thin
atmosphere? Why does a less massive moon of Saturn have a more extensive
atmosphere than Mars?
-
What two basic things are thought to be needed to create a magnetic
field? What is the magnetic dynamo theory?
-
Why is there so much convective motion in many planet atmospheres and some
planetary interiors?
-
What are the various types of meteorites? What distinguishes them? Which
type(s) can be ``primitive''? Where did the various types originate from?
Which are most common; least common? How do we know?
-
What are chondrules? Why are they important for solar system
formation models? What type of meteorite are they likely to be found in? Why not the other types?
-
What type of ``age'' does radioactive dating tell us? How does it work?
What's a half-life? How old are the primitive meteorites? How old are the
oldest Earth rocks on the surface? How old is the Earth? If
= 4
billion years and I know that a sample contains 1/8 its original amount of a
radioactive isotope, how old is the sample?
-
How do meteorites give us clues to the original conditions of the solar
system?
-
What are the two sources of meteoritic material? What is a meteor
shower?
-
Where do most comets from? What is the Oort cloud? Where is it? What
observations led to the proposal for the Oort cloud's existence?
-
How do comets give us clues to the orginal conditions of the solar
system?
-
What happens to a comet's nucleus as it approaches the sun? Which way
does the tail point?
-
What observed facts does the condensation theory of the Solar System
formation explain? Why are the inner terrestrial planets small and rocky while
the outer Jovian planets are large and gaseous?
-
Why is the density of the planets higher in close to the Sun than the
ones further out?
-
What are the two main gases in the sun? How does its mass and size
compare with Jupiter?
-
What is the photosphere of the sun? What two ways can we use to find
that the photosphere is about 6000 K? How?
-
What are sunspots? What are some the characteristics of them? What
is the sunspot cycle? What are prominences and flares? What role
does the magnetic field play? What is granulation?
-
Do all surface layers of the sun rotate at the same rate? How can we
tell?
-
What are the chromosphere and corona? How can we tell that
they are over 6000 K (some parts reaching a few million degrees). What
are coronal holes?
-
Where are the core and convection zone of the sun? What goes on in
them?
-
What is nuclear fusion? How can it produce energy? Why does it
need high temperatures? Why is it so hard to develop nuclear fusion as a
dependable power source on Earth?
-
Why won't chemical reactions or gravitational contraction work for
powering the sun?
-
What is the net result of the proton-proton chain? Why does nature use
the chain process instead of a one-step fusion procedure?
-
What are neutrinos? Where are they produced? What information can
they tell us about interior conditions in the sun? What is the solar
neutrino problem? What could be possible solutions to it?
-
What is luminosity? What two things does it depend on? How can we
use the luminosity to find the lifetime of the sun?
-
What is the magnitude system for specifying the brightness of objects?
What does a magnitude interval of 5 correspond to in brightness? How
about an interval of 1? How about an interval of 3? Do bright things have
larger or smaller magnitudes than fainter things? What is apparent
magnitude? How is it different from absolute magnitude?
-
What do astronomers mean by B-V colors? How can the colors
indicate the temperature?
-
What is a spectral type for stars? What are the basic spectral types of
stars and their order in terms of temperature, mass, and luminosity? What does the
spectral type depend on? Why do some stars have strong Hydrogen lines and other
stars do not, even though all stars are approximately 90% Hydrogen?
-
What two ways can we use to find the temperature of a star? How can
astronomers use the presence or absence of certain spectral lines to
find the temp. of a star? Why is looking for which spectral lines are present
as well as their strength (how dark the absorption lines are or how bright the
emission lines are) the most accurate way to get the temp.? (Think about
where a hot O star would have its continuum peak and where a cool M star would
have its peak color brightness.)
-
What is the Inverse Square Law for light? If I have two 100 watt
light bulbs at two different distances from me, one four times further away than
the other, which one will appear brighter and how many times brighter than the
other bulb will it appear?
-
What is trigonometric parallax? What is it used for? What is the
procedure? What do we need to know in order to use this procedure? Would using
an observatory orbiting the sun at the distance of Jupiter be an improvement?
Why? What is spectroscopic parallax? What is a parsec?
-
What are some basic differences between stars and planets?
-
What are the different kinds of binary stars? How are binary stars useful
for determining typical characteristics of stars?
-
What is the range of temperatures found on the photospheres of stars? What is
the range of luminosities produced by stars? What is the range of masses of stars?
-
How can we find masses and diameters of stars? How do we use a plot of
radial velocity vs. time to find orbital period and masses? Does the lighter
star move faster or slower than the heavier star? Which famous law of motion do
we use to find masses? How do we use a plot of a binary star system's brightness vs.
time to find the diameters of stars?
-
What is an equation of state? What astronomical problems require
knowledge of the equation of state?
-
What is hydrostatic equilibrium? What is being equilibrated? How
does hydrostatic equilibrium control the fusion rate in the sun? What happens
to the size of a star if its core steadily produces more/less energy than
it did at some earlier time? Do photons produced in the core zip right out from the
sun or does it take longer? Why?
-
What is the Color-Magnitude (CM) diagram (also called a Hertzsprung-Russell (HR) diagram)? Where would red giants be
plotted? What is the main sequence? Where would white dwarfs be plotted?
Which main sequence stars are hotter and which are cooler? Which ones are more
massive and which ones are the lightweights? Which main sequence stars are
bigger in diameter than others? How can you tell that they are bigger?
-
Are red giants or supergiants very massive stars? Why are red giants so
big and red? What is going on inside the giants?
-
Which main sequence stars last for a short time as main sequence stars?
Which ones last a long time? Why is that? How can we use a cluster's CM
diagram to find the age of the cluster? What can the main sequence turnoff
(MST) tell you? What assumptions do we make in this age-dating
method of MST? How do we know that a cluster with a MST of 3 solar masses is
younger than a cluster with a MST of 2.8 solar masses and older than a cluster
with a MST of 3.2 solar masses?
-
Would you expect some short-lived stage of a star to be always seen in
a ``snapshot'' of a cluster's CM diagram? What do you think a snapshot of a
cluster's CM diagram might show as far as the presence of certain short-duration
stages of a star's evolution and the presence of certain long-duration stages?
-
Which spectral classes are more common than others? How do we know without
having to survey the entire galaxy? How can we get a representative sample
of stars? Why is using an apparent brightness selection method a biased
way of selecting stars?
-
What fundamental property of stars will determine their evolution? What
happens to a main sequence star that has stopped fusing Hydrogen in its
core? What is shell-burning? What will happen to our sun? How long is its
main sequence lifetime? What will happen to a hot, blue star (> 10 solar
masses) during its entire lifetime? What will happen to a cool, red star
(< 0.5 solar masses) during its entire lifetime?
-
What goes on in the cores of evolved (post main sequence) stars? Where
did elements heavier than hydrogen and helium come from? What do we mean by
stellar nucleosynthesis? Why is iron the limit for stellar
nucleosynthesis in red giants? Where did heavier elements than iron come from?
-
What is a supernova? Which main sequence stars will eventually
supernova? What is a nova? How is it different from a supernova? About how
often does a supernova occur in a typical galaxy? Why is it better to look for
supernovae in other galaxies?
-
What is a white dwarf? What keeps a white dwarf from collapsing to a
point at the center? What is electron degeneracy pressure? What is the
upper bound for the mass of a white dwarf? How would the fact that stars up to
5 solar masses become white dwarfs show that stars lose mass to the
interstellar medium as they evolve? What is a planetary nebula?
-
What is a neutron star? How is it created? What keeps a neutron star
from collapsing to a point at the center? What is neutron degeneracy
pressure? What are the ingredients for a pulsar? Why does a pulsar spin so fast?
What is the upper bound for the mass of a neutron star? Why could a collapsed
star spinning many times each second not be a regular star or white dwarf?
-
What is a black hole? Does anything keep it from collapsing to a
point at the center? What is the Schwarzchild radius or event
horizon? What is the sole determining thing that specifies the size of the
event horizon? What are the signatures of a black hole-observations indicating
the presence of a super-compact nearly invisible object?
-
When are the unusual effects predicted by special relativity and
general relativity theories particularly noticeable? Have we been able to
test these two theories of Einstein? If yes, how so? If not, why not?
-
What kind of galaxy do we live in? What is the name for our galaxy? How
big is our galaxy? How many stars are in it and how do we know? Where are we
in the galaxy and how do we know? What can the distribution of globular clusters
tell us about our place in the galaxy? How so?
-
What are the four basic components of our galaxy? Where would old stars
be found? Where would stars with very small amounts of ``metals'' (elements
heavier than Helium) be found? Where are new stars being formed? Where would
stars enriched with ``metals'' be found?
-
What is meant by a standard candle? How are Cepheids and RR-Lyrae
stars considered to be standard candles? How would cluster main sequences be
considered to be standard candles? What is the period-luminosity relation
of Cepheids? How can we use it to find distances? How will the fixed Hubble
Space Telescope help?
-
Why do variable stars like Cepheids, RR-Lyrae stars, and Mira variables
vary in brightness?
-
What is meant by a standard ruler? How would the angular sizes
of globular clusters or H II regions be used as standard rulers?
-
What is the interstellar medium (ISM)? How does it affect starlight?
-
How do we know that the non-gaseous part of the ISM cannot be
made of rocks but, rather, of small ``dust'' particles? What is meant by
reddening and extinction of starlight? How are these effects produced?
Where is the dust thought to come from?
-
What are the characteristics of the gaseous part of the ISM? Is the gas all
at the same temperature and density? How do we know? What are H II regions?
What produces them? What is going on at the atomic level? How does the gas
far from any star make its presence seen in the optical wavelengths and radio
wavelengths? How are the complex molecules in the ISM likely to have formed?
-
What produces the 21 cm radiation? How is it produced? Why is it so
important for determining galactic structure and mass? How do we use it to
determine galactic structure and mass?
-
What is a galaxy? What is a typical size of a galaxy? What is a
typical number of stars in a galaxy? How do we know? What separates a cluster
of stars from a galaxy?
-
What are four basic distinguishing characteristics between a spiral galaxy
and an elliptical galaxy? What kind of galaxy do we live in?
-
What are the theories for how spiral arms are formed and maintained? What
are the verifiable predictions made by these theories?
-
What is the most common type of galaxy? Why are irregular galaxies
called irregulars?
-
Why do we see more galaxies when we look in a direction perpendicular to
the Galactic plane than when we look along Galactic plane?
-
What is a cluster of galaxies? Are we in one? What is the nearest large
cluster of galaxies to us? What kind of galaxy is typically found near the
center of a large cluster of galaxies? Why is that kind of galaxy so big?
-
Why is the spatial distribution of clusters of galaxies sometimes
described as a foamy structure or like edges of soap bubbles? How do we know
that the clusters have this spatial distribution?
-
What are the more accurate or more certain ways to measure distances? What are the less accurate (less certain) ways to measure distances? What assumptions do we make when using the less certain techniques? Why is finding accurate
extragalactic distances so important?
-
What is the Hubble law? What two things does it relate? Why is it
important? What is the Hubble constant (
)? What can the Hubble
constant tell us? How would the age of the universe change if was 50
instead
of 100 ?
Is the Hubble constant actually constant throughout time? Why or why not?
-
How do we know that the universe is expanding? What is meant by a
uniform expansion? Would all galaxies at a certain cosmological time
find the same Hubble law? Why or why not?
-
What would the relation between the radial velocity and distance be if
there was no expansion? What would the relation be if the universe was
contracting?
-
Is there a center to the expansion in normal 3D space? Why or why not?
Why do we use the analogy of beads on an expanding balloon or a raisin cake to
try to picture the expansion?
-
Is the space between stars inside a galaxy expanding? Why or why
not? Is the space between the molecules in your body expanding with the
universe? Why or why not?
-
How is looking at faraway objects equivalent to looking back in time?
-
What is a quasar? What makes us believe that they are very far
away? What observations show that they are very luminous and that the power
is generated within a small volume (solar system-size space)? What is
thought to power the quasars?
-
What is all the fuss about Dark Matter? If it is not putting out
any light for us to see, how do we know that it exists? What are some
examples of observations indicating its presence?
-
What is a rotation curve? How can it tell us the distribution of
matter in a galaxy? Why would a flat rotation curve be an indication of
the presence of dark matter?
-
Why is the universe's expansion rate slowing down? Will it ever slow down
completely? How can we find out? What is meant by critical density
(
)? What would
happen to the expansion if 
?
How about 
? Would a
universe starting out with
ever expand enough so its density dropped below ?
Why or why not?
-
What is meant by a closed or open or flat universe?
-
What is the cosmological principle? What is the perfect cosmological
principle? Which one can an evolving universe fit in? Why?
-
What is the steady state theory of the universe? What is the Big
Bang theory of the universe? Which of the cosmological principles above do they use?
-
What is the evidence for a Big Bang type of model for the universe? Are
they really proofs for the Big Bang or are they proofs against the
steady state theory? How do we know that the universe has evolved over time?
-
What is the Cosmic Microwave Background Radiation? What is it a
relic of? Is it really perfectly uniform? If there are deviations from perfect
uniformity, what would be the cause? What is the type of spectrum of the
background radiation? What is the temperature? Why did recombination and the
decoupling of matter and energy happen at the same time?
-
About when did the Big Bang supposedly occur? What was the universe like
for the first few million years after the Big Bang? How was the early universe
like the cores of stars shining today?
-
Where did most of the Hydrogen and Helium in the universe come from? How
about the deuterium? Why did the early universe not continue the
nucleosynthesis process to heavier nuclei?
-
How does the present abundance of deuterium provide a good constraint on
the current density of the universe?
-
What is Olber's Paradox? Why is the night sky dark? What important
conclusions can we draw from the simple observation that the night sky is dark?
-
What evidence do we have of other planetary systems forming? Where have
extrasolar planets, protoplanets, or disks around stars been found?
-
Where do we expect to find extraterrestrial intelligent life? How do we
guess how many other communicating civilizations we expect to find? What parts
of that guess are fairly well-known and what parts are much more uncertain?
Nick Strobel --
Email:
strobel@astro.washington.edu
(206) 543-1979
University of Washington
Astronomy
Box 351580
Seattle, WA 98195-1580