Download Objectives for Units 1-3

GSC 1580 Objectives – Test 1 (Units 1-3)*
Unit 1
1. State four proofs that the Earth is approximately spherical.
a. If the Earth were flat, objects would simply get smaller as they moved
away. A ship’s hull always disappears below the horizon regardless of the
direction it sails. The only geometrical shape curved equally in all
directions is a sphere.
b. The Greeks correctly considered lunar eclipses to be due to the shadow of
the Earth on the Moon when the Sun and Moon are on opposite sides of
the Earth. The only geometrical shape that casts a circular shadow in all
directions is a sphere.
c. The first direct proof that the Earth is a sphere was the voyage of Magellan
around the world.
d. Pictures from space.
2. State the origin of the names of the days of the week.
a. The names of the week are derived from the seven heavenly bodies that
wander relative to the fixed background stars. [Sunday (Sun), Monday
(Moon), Tuesday (Tiw, Old English, Mars) Wednesday (Woden’s Day,
Old English for Norse god Odin, Mercury) Thursday (Thor, Old Norse,
Jupiter,) Friday (Frigg, Old English word for Norse god Fregg, wife of
Odin, from prehistoric translation for dies Veneris, Venus’ day, Venus)
Saturday (Saturn, Latin.)]
3. Explain the following terms:
a. Parallax: the apparent change in the position of an object due to an actual
change in the position of the observer.
b. Geocentric system: (Ptolemaic) A system in which the Earth is the center.
c. Heliocentric system: (Copernican) A system in which the Sun is the
center.
d. Retrograde motion: Having or being motion in a direction contrary to that
of the general motion of similar bodies and especially east to west among
the stars.
e. Epicycles: Small loops proposed by Ptolemy to explain retrograde motion
in the orbits of planets.
4. State the diameter of the Earth.
a. The Earth is approximately 8,000 miles in diameter (7,926.) The earliest
accurate estimate was proposed by Eratosthenes, who used the shadows of
the Sun at different points on the Earth’s surface to measure the a rough
estimate of the Earth’s circumference (using the formula r2.)
5. State the major contribution to astronomy of each of the following persons, and
identify the moon craters named for each of them:
a. Eratosthenes: Made the best early determination of the Earth’s size
b. Ptolemy: Proposed and extended the Ptolemaic or geocentric system.
c. Copernicus: Proposed that the stars are stationary, the Sun is the center of
the universe (heliocentric), and that heavenly bodies move in perfect
circles and at constant speeds.
d. Tycho: Provided years of systematic and accurate observations that were
vital to Kepler’s system of laws. First observed that celestial bodies move
in non-circular orbits.
e. Kepler: Proposed Kepler’s Laws, which proposed that the orbit of a planet
is an ellipse, planets travel faster when they near the Sun in their orbits,
and that the further away from the Sun, the slower the speed of the object.
6. State three proposals by Copernicus and the implications of each.
a. The stars are stationary. Implies that the Earth rotates once daily.
b. The Sun is the center of the universe. Implies that the Earth revolves once
yearly.
c. Heavenly bodies move in perfect circles at constant speeds. Implies that
the planets also revolve around the Sun, and thus through the night sky.
7. Distinguish between rotation and revolution.
a. Rotation is the act of a body spinning around an axis.
b. Revolution is the act of a body orbiting a point in space.
8. State the major contribution to astronomy of Galileo.
a. He was the first person to point a telescope toward the heavens and was
the first man to see the mountains and craters of the Moon. He was the
first to detect the four largest moons of Jupiter, the phases of Venus, and
Sunspots.
b.
9. Answer questions regarding Kepler’s Laws and the qualitative application of each
of them.
a. The motion of a planet is an ellipse with the Sun at one focus. An ellipse is
the normal shape for any orbit.
b. The line from a planet to the Sun sweeps out equal areas in equal times. A
given planet goes faster when it is close to the Sun and slower when it is
farther away.
c. The square of the orbital period of a planet is proportional to the cube of
its average distance from the Sun. Those closer to the Sun go faster, and
those farther away go slower.
10. State six proofs that Earth rotates.
a. Satellites in low Earth orbits change positions relative to the Earth’s
surface on each pass because the satellite maintains its original path while
the Earth rotates beneath it.
b. If a pendulum were to be placed at the North Pole, to the observer (over
time) the pendulum would change directions. In reality, it is the observer
that is changing position (due to the Earth’s rotation) in relation to the
pendulum.
c. The oblate spheroid shape of the Earth stretches the spherical shape
outwards, where the circumference at the equator is larger than that
through both the North and South Poles.
d. Falling objects fall to the East because the Earth rotates.
e. The Moon approaches at 600 mph at Moonrise and recedes at the same
rate at Moonset. (The earth rotates at a constant speed.)
f. All weather formations are rotating due to the effect of Coriolis forces,
which are always present on a rotating platform.
11. State three proofs that the Earth revolves
a. Stellar parallax creates the appearance of little loops over the course of
time. The apparent pattern is an ellipse (similar in shape to the Earth’s
orbit) for those stars at right angles to the plane of Earth’s orbit, and
straight lines for those stars parallel to Earth’s orbit.
b. The aberration of starlight when stars are viewed from Earth causes
astronomers to change the tilt of their telescopes over time to compensate
for the Earth’s orbital motion.
c. Certain stars approach us at one time, and six months later are receding.
(Observed using changes in Doppler shift.)
Unit 2
1. Distinguish between a solar and sidereal day.
a. A solar day is the most familiar of the two, and lasts 24 hours. This is the
time it takes for the Earth to make one rotation. It is measured with respect
to the Sun.
b. A sidereal day is measured in respect to the stars. It is the time it takes for
the Earth to rotate and face the same star. It is slightly shorter than a solar
day and is 23 hours, 56 minutes, 4.099 seconds long.
2. Explain the meaning of the precession of the Earth, and answer simple questions
concerning it.
a. The Earth’s axis rotates on a 23.5 degree angle, which itself spins around
over time like a top. The axis itself precesses over a 26,000-year period.
Polaris is our current north star, but in 14,000 AD Vega will be our north
star due to this precession.
3. Explain the significance of the Tropics of Cancer, Capricorn, the Artic and
Antarctic Circles in astronomical and seasonal terms.
a. Tropic of Cancer: most northerly line on the Earth’s surface where the
Sun’s rays hit vertically. It is the key to determining the first day of
summer.
b. Tropic of Capricorn: most southerly line on the Earth’s surface where the
Sun’s rays hit vertically. Key to determining the first day of winter.
c. Artic Circle: Most southerly line in the Northern Hemisphere where 24
hours of darkness/Sunlight is possible.
d. Antarctic Circle: Most northerly line in the Southern Hemisphere where
24 hours of darkness/Sunlight is possible.
4. Explain the following units of time in astronomical terms: day, week, month, and
year.
a. Day: The time it takes a planet or moon to rotate around its axis once.
b. Week: An Earth term that lasts seven Earth days, possibly due to the seven
heavenly wanderers.
c. Month: The time it takes for the Moon to revolve around the Earth.
d. Year: The time it takes for the Earth to revolve around the Sun.
5. See Moon Map.
6. Answer qualitative questions concerning Newton’s law of gravitation.
a. An object’s mass is the amount of matter contained within it. An object’s
mass remains constant. The greater the mass, the greater the pull it has on
other objects. Thus, the Moon revolves around the Earth because Earth’s
mass is greater than the Moon’s, and therefore pulls on the Moon with
enough force to keep it in orbit. The less mass an object has, the less
gravitational force it has. Weight is different than gravity. Weight is a
measure of gravitational forces pulling on an object, and changes with the
amount of mass. This is why you weigh less on the Moon. The less the
distance, the greater the force.
7. Discuss Earth’s structure based on density and on magnetic field considerations.
a. Density is an object’s mass divided by its volume. Water’s density is 1
g/cc. The density of the Earth is approximately 5.5g/cc. The rocks and soil
on the surface of the Earth have an average density of about 3.3g/cc. Thus,
the earth is denser at its center than at its surface. The density of the core
is thought to be slightly over 8g/cc. The core itself is made of molten
materials, churning and creating heat and radiation. The magnetic fields of
Earth’s atmosphere are created from the movement of a liquid iron core.
Charged particles from space are trapped in the upper atmospheric
magnetic field, which creates the wonderful spectacle of the aurora
borealis. The magnetic field protects Earth from harmful radiation.
8. Answer questions about orbital motion.
a. All orbital paths are in the shape of an ellipse. Orbital motion causes the
Earth’s axis to point in the same direction at different points in its
revolution, causing the amount of Sunlight to reach the surface to become
more and less concentrated, allowing the seasons to change. Orbital
motion of the moon results in its rising 50 minutes later each day.
9. Diagram the relative positions of the Earth, Moon and Sun for various phases of
the Moon as seen from Earth, or Earth as seen from the moon.
10. State the distance from the Earth to the Moon and the size of the Moon, in miles.
a. The distance from the center of the Earth to the center of the Moon is
240,000 miles. The Moon is about 2,140 miles in diameter, roughly ¼ of
the diameter of Earth.
11. State the length of daylight and night on the Moon in terms of Earth time.
a. One lunar day is equal to one Earth month, the time it takes the Moon to
revolve once around the Earth. On the surface of the Moon, daylight stays
for an entire month, followed by an entire month of darkness.
12. Discuss the Moon’s structure based on density and magnetic field considerations.
a. The Moon is less dense than the Earth. The density of the Moon is roughly
equal to the density of the surface of Earth. The Moon also has dense
pockets of matter in the maria, or lunar oceans, where impact craters are
thought to have pierced the surface and allowed molten rock to fill in the
surface. The Moon does not have a magnetic field like the Earth, mostly
due to the lack of a molten iron core similar to that on Earth.
Unit 3
1. Explain the origins of tides, distinguish between neap and spring tides, and
answer questions about tides.
a. The tides are created by the gravitational pull of the Moon and Sun on the
Earth’s oceans. There are two high tides each day. The first occurs on the
side closest to the Moon, where the gravitational forces pull the waters
closer to the Moon, allowing a high tide. On the opposite side of the Earth,
the same forces pull greater on the Earth, causing the waters to rise as
well. A spring tide occurs when the Sun and the Moon pull on the Earth’s
oceans during a New or Full Moon. These tides are higher than an average
high tide. A neap tide occurs when the Moon is in the First or Third
Quarter phase, where the Moon forms a high tide in one place while the
Sun forms a high tide where the Moon causes a low tide. These produce
high tides that are lower than average. The high and low tides rise and fall
about 50 minutes later each day due to the Moon’s revolution.
2. Explain why eclipses don’t occur monthly, and distinguish between annular and
total eclipses.
a. The reason why eclipses do not occur monthly is because of the 5-degree
angle of the Moon’s orbit. The Moon must be directly in the path of the
Sun or the Earth must be directly in the path of the Moon to create an
eclipse. A total solar eclipse occurs when the Sun is completely blocked
by the Moon. An annular solar eclipse occurs when the Moon partially
blocks the Sun, but due to the distance of the Moon’s elliptical orbit, it
remains further from Earth, thus creating the ring-like appearance.
Likewise, there are lunar eclipses, where the Earth’s shadow completely
covers the Moon.
3. Relate the lack of limb darkening to the Moon’s surface texture.
a. The surface of the moon is covered in a fine dust, which is the result of
thousands of years of radiation breaking the rocks on the Moon’s surface
down into fine particles. The Moon exhibits little limb darkening; its edge
is not noticeably darker than its center. The low reflectivity and lack of
limb darkening suggest the surface of the moon is rough on both a large
and small scale.
4. Explain how it was possible to predict the Moon has no atmosphere.
a. Using the kinetic theory of gases, it was shown that gas molecules in the
high daytime temperatures on the Moon travel faster than the Moon’s
escape velocity of 1.7 miles per second. Thus, the Moon could not
possibly have an atmosphere.
5. Discuss the two major theories for the origin of lunar craters.
a. The first theory is that the craters were created from volcanic activity.
Clouds of gases observed from Earth are thought to be the result of such
activity. Surface rocks returned to Earth also support evidence of volcanic
activity on the moon.
b. The second theory is that the craters were formed from objects impacting
the surface over millions of years. There is evidence for ancient and new
impact craters on the surface of the Moon.
6. Explain the probable origin of the lunar maria.
a. The probable origin of the lunar maria is that large objects pierced the
surface of the moon, allowing liquid magma to fill the remaining crater.
This created vast areas of cooling rock that appear smooth and have
greater densities than the surface rocks surrounding the maria.
7. State four ways the Moon may have originated.
a. The first theory suggests it was formed elsewhere and was captured as it
passed the Earth. (The adoption theory.)
b. The second suggests that the Moon was formed and evolved right along
with earth. (The twins theory.)
c. The third suggests that the Moon was once part of the Earth, and as denser
material sank towards the center, lighter material was thrown into orbit
and created the Moon. (The entire moon has the same density of the
surface of the Earth. The spinning spitter theory.)
d. The fourth theory suggests that the Moon was created by a catastrophic
collision with a very large object, roughly the size of Mars. The collision
created the Moon out of the Earth. (The fender bender theory.)
8. Explain how the relative age of ray craters may be determined.
a. A new lunar impact crater sprays white rocks and debris across the
surrounding surface. Over time, these rocks turn dark due to the constant
weathering from the solar winds. Thus, a newer impact crater has lighter,
whiter surface features and older impact craters appear much darker.
*
Note: The information contained within this document is for studying purposes only. Do not duplicate this document for any other
purpose. It is basically a paraphrased version of the class notes, available in the OCC bookstore, organized into a structure matching
the required objectives for each group of units.