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Astronomy 108/110 review for Exam #1
The material on this exam can be broken down into four broad catagories: a
quick introduction to the night sky, astronomy as a case history of science,
some notes on physics, and an overview of the planets.
From the quick introduction to the night sky you should understand:
• What the celestial sphere is. If it is real.
• What the celestial north pole is and how the north star relates to it.
• The horizon coordinate system for identifying to a friend which star you
are looking at in the sky.
• The path a star sweeps out in the course of one night, what a circumpolar
star is, how the movement of stars through the night sky is related to the
latitude of the observer.
• Retrograde motion and what exhibits it.
• Why summers on earth are hot and winters are cold.
• How the Zodiac helps you to predict the future.
• The phases of the moon; that is what causes them and what order they
fall in.
From Astronomy as a case history of science you should understand:
• That science is a method for making sense of the world. That it involves
building models that are consistent with the observations of the world
at the time the models are made. That when observations provide new
information that is not consistent with the existing models new models
are made that are either small modifications of the old model, or large
changes that fundamental assumptions that went into the old model.
• That historically the science of astronomy has evolved from: making casual
observation of the sun, stars, moon, and planets → ordered written records
of the locations at specific times of the sun, stars, etc. → recognizing order
in these records → the building of mechanical models that give a rational
for the order that is seen.
• The understanding of the above should include familiarity with examples of the following models:Pythagorean model (first mechanical model),
Ptolomey’s model (geocentric, epicycles explain retrograde motion of the
planets, everything but the earth moves on a circle), and Copernicus (geocentric, planets and the moon move on circle, also had epicycles but not
to explain retrograde motion, what mechanism causes retrograde motion
of planets).
• What happened to ancient Greek and Roman astronomical knowledge
between the fall of Rome and the Renaissance.
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• What Tycho Brahe did, who he left his results to.
• Kepler’s 3 laws of motion
1. Planets move in elliptical orbits with the Sun at one focus of the
ellipse.
2. The line connecting the sun to a planet sweeps out equal areas in
equal times.
3. When the period of time, P it takes a planet to orbit the sun is
measured in earth years and the semi-major axis, a, of the planet’s
orbit is measured in terms of the earth’s semi-major axis P 2 = a3 .
• What Galileo saw through his telescope; the moons of Jupiter, the phases
of Venus.
From the notes on physics you should understand:
• Objects move in straight lines unless acted upon by an external force.
• Circular motion is not a natural state of motion, a force is required to
make an object move in a circle.
• A net force, f , on an object with mass m causes an acceleration, a, and
the size of the acceleration is equal to a = f /m in the direction of the net
force.
• There can be multiple forces but no net force (think tug of war)
• When Alice exerts a force on Bob, Bob also feels a force, one that is equal
and opposite to the force Alice feels.
• Gravity is what causes the planets to move in elliptical orbits around
the sun, and what causes moons to move in elliptical orbits around their
planets.
• Escape velocity is the minimum speed an object must be moving away
from a planet at to get away from the planet. The more massive the
planet the larger the escape velocity.
• What a tidal force is, what causes it, what makes it strong in some situations and week in others.
• Electromagnetic radiation is our best probe of distant objects.
• Why when we look at a distant star we are seeing the star how it was and
not the way it currently is.
• You should have a general sense of the electromagnetic spectrum, that:
– radio waves correspond to wavelengths on the order of km (1000m)
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– microwaves wavelengths of mm(.001m)
– infrared(heat) wavelengths of µm (.000001m)
– visible light wavelengths of about 0.5µm
– that ultraviolet, x-rays, and gamma waves are progressively smaller
wavelengths of light.
• What reflection and refraction are and why they are useful.
• What dispersion is and why it is useful.
• What the 2 main purposes of a telescope are.
• What black body radiation and spectral radiation are, the difference between them, and the difference between what makes them.
• That the temperature of an object is related to how fast its molecules are
moving.
• That a hot gas takes up more volume than a cold one at the same pressure.
• Why the pressure at the surface of a planet is higher than the pressure in
the upper atmosphere of the planet.
• The three major sources of heat at a planet.
From the overview of the planets you should understand:
About the earth
• How we know the earth is spinning and revolving around the sun instead
of being fixed in space.
• The general structure of the earth including its interior (core, mantel,
crust), surface (ocean and mountains) and atmosphere (troposphere–where
life is, stratosphere–where jets fly, mesosphere–where the ozone layer is,
ionosphere–what radio waves bounce off of).
• How we know about the earth’s interior (core, mantel, crust).
• What the atmosphere is made of (78
• What the magnetosphere is, how we see it, why it is important for life on
earth.
About the Moon
• Why the same side of the moon always faces the earth.
• What is a solar eclipse, lunar eclipse.
• What causes the tides.
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• Features of the moon’s surface (terrae, maria, craters) and what causes
them.
• The best current model for the formation of the moon and what data
it incorperates (orbit parallel to the rotation of the earth, similar crusts,
small iron core).
Facts about the other planets
• Size relative to earth, Re : Mercury and Mars ∼ 1/2Re Venus ∼ Re , Jupiter
and Saturn ∼ 10Re , Uranus and Neptune ∼ 4Re , and Pluto ∼ 1/4Re .
• The planets-sun distance relative to the earth-sun distance Mercury∼
0.4AU, Venus∼ 0.7AU, Earth 1.0AU, Mars∼ 1.5AU, Jupiter∼ 5AU, Saturn∼
10AU, Uranus∼ 20AU, Neptune∼ 30AU, Pluto∼ 40AU.
About each planet’s story
• Mercury: surface(intercrater plains, smooth plains, scarps), rotation (hot
poles and cold poles), best current model for Mercury’s evolution, why
doesn’t Mercury have much of an atmosphere, why Mercury is a hot and
cold place.
• Venus: retrograde rotation, Atmosphere composition(97%CO2 , 4%N2 ),
day temperature vs night temperature.
• Mars: water[where has it been(rivers, oceans, ice caps), where is it now
(maybe ice caps, really an open question), what form(once was liquid, now
pressure to low and it can be a gas or a solid only)], Atmosphere(CO2 ,
N2 , Ar, and lots of dust), why the Hawaiian Islands are so much smaller
than Olympus Mons, why humans were “sure” that there were martians
circa 1910AD.
• Jupiter: Biggest planet in solar system 1/10th the size of the sun, mostly
Hydrogen and Helium, interplay between banded appearance zonal winds
the earth’s jet stream and large scale storms, the Great Red Spot, faint
rings, currently gives off more energy than the sun shines on it, metallic
Hydrogen planet size and magnetic field.
• Saturn: Biggest ring system in solar system, mostly Hydrogen and Helium less dense than liquid water, faint bands zonal winds etc., metallic
Hydrogen planet size and magnetic field.
• Uranus: discovery (1781), no banding zonal winds etc., only gives off as
much energy as comes from the sun, spins on its side, black rings.
• Neptune: discovered circa 1850 by closely observing Uranus’ orbit, banded
appearance zonal winds large scale storms currently gives off more energy
than it absorbs from sun, faint rings.
• Pluto: discovered circa 1930 by apparent discrepencies in Uranus’ orbit,
only planet not yet visited by space craft, odd-ball orbit.
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