Astronomy Test 3
What is surprising about the extrasolar planets that have so far been discovered?
Many of the extrasolar planets are giant planets like Jupiter, orbiting at distances characteristic of terrestrial planets like Earth, where giant planets cannot form.
The asteroid belt exists between the orbits of which planets?
Mars and Jupiter
Which of the following significant features would be noticed by space travelers approaching Earth for the first time?
One hemisphere of Earth is almost entirely covered with water.
The region at the farthest limits of the solar system in which a large number of objects composed of rock and ice circle the Sun in a roughly spherical region is called the
Oort comet cloud.
How do we measure the mass of an extrasolar planet?
We use Newton's law of gravity, using the measured distance of the planet from its star and the planet's gravitational pull on the star
The presence of oxygen in Earth's atmosphere is thought to result directly from what type of process?
biological activity of plants and animals
What are spring tides?
high tides that are significantly higher than the average high tide
What are neap tides?
high tides that are significantly lower than the average high tide
At the present time, the discoveries of how many extrasolar planets have been confirmed?
hundreds
What were the dominant gases in Earth's earliest atmosphere after it first formed?
hydrogen and helium
The most common elements in the universe are
hydrogen and helium, with small amounts of heavier elements
Most of the mass of the universe—98%—is in the form of
hydrogen and helium.
The smooth, dark maria on the Moon are
immense impact basins that are smooth because they were covered by lava flows after the early, heavy bombardment had ended.
The mountains on the Moon were mostly caused by
impacts from interplanetary bodies from outer space.
Which of the following processes has played the greatest role in shaping the surface of the Moon?
impacts of interplanetary bodies of all sizes
Where was all the hydrogen in the universe formed?
in the Big Bang, at the very beginning of the universe
Where in the universe are heavy elements with masses greater than that of helium being produced at this time?
in the central cores of stars
The names we use for the Moon's maria were
invented a few hundred years ago after the first telescopic observations of the Moon.
The magnetic field of Earth
is related to its rotation around its axis.
The average density of a planet is
its total mass divided by its total volume.
What is a mare on the Moon?
large area of darker material on the lunar surface
What is the lunar regolith?
layer of fine powder covering the lunar surface
What is a lunar rille?
long, winding crack in the surface of a mare
Earth's solid inner core results from the fact that the
melting temperature of an iron-nickel mixture increases with increasing pressure and rises above the actual temperature in the inner core.
The coldest layer of Earth's atmosphere is located between
mesosphere and thermosphere.
Ozone is a gas consisting of
molecules containing three oxygen atoms.
The existence of the mid-Atlantic Ridge is evidence that Europe and North America are
moving farther apart.
A curious fact about the structure of the planet Jupiter, compared with the structure of Earth, is that it has
much greater mass but much lower average density.
What was the material from which the solar system formed?
nebula made mostly of hydrogen and helium gas but enriched in heavier elements from supernova explosions
Earth's thermosphere is the
outermost atmospheric layer in which ultraviolet light from the Sun ionizes atoms.
Earth's stratosphere is warmer than the layers above and below it because
ozone in the stratosphere absorbs specific wavelengths of ultraviolet radiation from the Sun.
Strong evidence for the existence of planetary systems in the process of formation around other stars comes from
periodic wobbling of the positions and spectral line displacements of several nearby stars.
Strong evidence for the existence of planetary systems in the process of formation around other stars comes from
photographs and infrared observations of disks of dust.
Craters are not apparent on Earth at the present time in the abundance seen on the Moon because
plate tectonics has returned cratered surface layers into Earth's interior, and weathering has obliterated the more recent craters.
There is very little hydrogen or helium in the inner part of the solar system today. We believe the reason for this is that
the intense radiation from the early Sun drove the light elements out of the inner solar system.
What fraction of the total mass of Earth's atmosphere is contained in the troposphere, the lowest layer of Earth's atmosphere?
75%
The lowest temperature in Earth's atmosphere occurs at an altitude of about
80 km.
The reason for the vast amount of hydrogen in the interior of Jupiter is probably that
the mass of the initial condensation of rocks at Jupiter's orbit was sufficient to attract vast amounts of gas to it.
Most of the weight of our bodies comes from heavy elements such as carbon and oxygen. This fact immediately tells us that
the solar system did not form directly from the material created by the Big Bang.
Earth's magnetic field protects Earth and its inhabitants from
the solar wind, which would otherwise irradiate and damage life forms if not deflected.
The reason for the alignment of the Moon with one face always toward Earth is that
tides due to gravitational forces from Earth, while the Moon was molten, slowed the Moon's rotation.
What are the major layers of Earth's atmosphere in the correct order from the surface upward?
troposphere, stratosphere, mesosphere, thermosphere
Of the 30 billion planets estimated to exist in the galaxy, about how many are believed to be in orbit around Sunlike stars?
two billion
The Moon produces tidal disturbances on the oceans of Earth. In general, there are
two high and two low tides per day.
The Mid-Atlantic Ridge in Earth's crust is a region where
two tectonic plates are slowly spreading apart.
How many "tidal bulges" caused by the Moon's gravity are there on Earth?
two, one facing (almost) directly toward the Moon and one facing (almost) directly away from the Moon
The hottest part of Earth's atmosphere is the
upper thermosphere
At what point in time do we say that the protosun became the Sun?
when thermonuclear fusion reactions began at its center
When do spring tides occur?
whenever the Earth, the Moon, and the Sun form a straight line, regardless of which side of Earth the Moon is on (i.e., twice a month at the times of full and new Moon)
When do neap tides occur?
whenever the Earth-Moon line makes a 90° angle to the Earth-Sun line
What percentage of the sunlight that falls on Earth is absorbed by Earth rather than reflected into space?
63%
What process created the lunar regolith?
cracking and pulverizing by meteoric bombardment
The maria on the Moon appear to be
craters filled with basalt from within the Moon.
Roughly how much denser was Earth's second atmosphere (i.e., how much gas was there in it?) compared with today's atmosphere?
100 times denser
The African and South American continents are separating at a rate of about 3 cm per year, according to the ideas of plate tectonics. If they are now 5000 km apart and have moved at a constant speed over this time, how long is it since they were in contact?
170 million years
The lowest temperature in Earth's atmosphere is about
200 K.
What percentage of the sunlight that falls on Earth is reflected into space?
37%
What is the ratio of nitrogen to oxygen in Earth's atmosphere?
4 parts nitrogen to 1 part oxygen
About how much has Earth's surface temperature changed since ad 1000?
5C
Many craters on the Moon are characterized by a central peak. What is the significance?
A central peak is characteristic of an impact crater formed by a shock wave.
Approximately how many major tectonic plates make up Earth's surface?
About a dozen
The first person postulated that continents drift around over Earth's surface?
Alfred Wegener
The composition of matter in the universe can be summarized by which statement?
All but 2% of the mass of the universe is hydrogen and helium.
The planet with the greatest mean density is
Earth.
Why did Earth's earliest atmosphere, composed primarily of hydrogen and helium, not last long?
Hydrogen and helium are light gases, and they soon escaped into space.
What is thought to be the physical mechanism that was responsible for the present mix of chemical elements in the universe?
Hydrogen and helium were formed in the Big Bang, whereas the heavier elements were made in the centers of stars.
The region outside the orbit of Neptune in which a large number of objects composed of rock and ice circle the Sun not far from the plane of the ecliptic is called the
Kuiper belt.
One or more natural satellites (moons) do NOT orbit which planets?
Mercury and Venus
The most noticeably elliptical planetary orbit is the orbit of
Mercury.
How was the Mid-Atlantic Ridge formed?
Molten rock pushed up from Earth's interior and forced two crustal plates apart.
Where are the asteroids located?
Most asteroids have orbits between the orbits of Mars and Jupiter, but there are gaps caused by resonances with Jupiter.
What is the relationship between the mantle and the crust of Earth?
New crust is formed by magma rising from the mantle in some places, and old crust is pushed back down into the mantle in other places.
Which is the most abundant gas in Earth's atmosphere?
Nitrogen
Ozone in the stratosphere performs an important task that protects life on Earth. What is it?
Ozone absorbs much of the dangerous solar ultraviolet light.
Pluto was originally classified as a planet, but new criteria for the definition of a planet were adopted, and Pluto failed to meet one of them. Which one?
Pluto does not have enough gravity to clear its orbit.
Which planet in our solar system has the lowest average density?
Saturn
In order of increasing density, the Jovian planets are
Saturn, Uranus, Jupiter, and Neptune.
How has the CO2 concentration in Earth's atmosphere changed over the past thousand years?
The CO2 concentration was relatively constant for about 800 years but has increased significantly since ad 1800.
Earth has an average density of 5500 kg/m3, although the density of rock on its surface is about 3000 kg/m3. What conclusion can be reached about Earth's core from this observation?
The Earth's core is made of material far denser than surface rock.
The most probable time sequence for the formation of the solar system was the following:
The Sun contracted first as a gas ball, and the planets and moons formed shortly afterward by accretion and condensation.
Why is the barycenter significant?
The barycenter is the common center of the orbital motions of Earth and the Moon due to their mutual gravitational attraction.
We have found that the upper layers of the mantle are "plastic." Why is this important?
The continents are able to float and drift on these layers.
Why do the larger craters on the Moon have central peaks?
The crater floor rebounded upward after the initial compression from the impact of an interplanetary rock.
A theory of the origin of the solar system must take into account all important general properties of the planets, which include three of the four properties listed. Which one is NOT an important general property of the planets?
The magnetic fields of the planets are produced by a variety of mechanisms.
How do the near and far sides of the Moon compare?
The near side has several large maria, or "seas," whereas the far side has only one small mare.
Why did the temperature start to rise at the center of the solar nebula?
The nebula was contracting, which increased the speed of the atoms moving in it.
What is the current status of Earth's ozone layer?
The ozone layer has been somewhat depleted, but if left alone, it could restore itself in a century.
The pressure in the atmosphere of Earth (or of any other planet) is related to altitude above the planet's surface in what characteristic way?
The pressure decreases by a fixed fraction each interval of altitude (down by ½ every 5.5 km on Earth).
How does the temperature of Earth's atmosphere vary with height over the range 0-80 km?
The temperature decreases, then increases, then decreases again. The temperature rises steadily until it reaches a high and constant value above 80 km.
The atmosphere that we are now breathing is the _____ atmosphere Earth has had.
Third
What is a typical speed of drift for a continent sliding over Earth's surface?
a few centimeters per year
The water on the side of Earth that faces away from the Moon experiences
a high tide because the combination of Earth's motion and the Moon's gravity makes water move away from the Moon toward the far side of Earth.
An "ozone hole" is
a region of the stratosphere above the South Pole where ozone levels occasionally drop to very low levels.
Moons have been discovered around
all the planets except those nearer to the Sun than Earth is.
Maria are
ancient lava floodplains
Most extrasolar planets have been found
around stars in the disk of our Galaxy.
Where is the mantle of Earth located?
between the core and the crust
What were the dominant gases in Earth's second atmosphere?
carbon dioxide and nitrogen
What is the barycenter?
center of mass of the Earth-Moon system
Comets are typically
chunks of ice that begin to vaporize if they pass close to the Sun.
"Continental drift" on Earth is now thought to be caused by
circulation currents in the deep interior, causing slabs of Earth's crust to move slowly.
The average density of the large, outer planets is
close to the density of water.
The nebular hypothesis of the formation of the solar system assumes that the material that became the solar system began as a large spherical cloud of gas and dust, rotating slowly. As the solar system formed, most of this material was transformed into a compact, flattened disk, rotating more rapidly. What is the explanation for this change in shape and rate of rotation?
conservation of angular momentum
The motions of large portions of Earth's surface, the plates, are caused by
convective flow of material in Earth's interior.
The birthplace of the Sun and planets (and of other stars and maybe their planets) is thought to have been in
cool gas and dust clouds.
Deep oceanic trenches on Earth are locations at
cool surface material on Earth sinks below other material at a tectonic plate boundary.
Subduction on Earth is the process by which
cool surface material on Earth sinks below other material at a tectonic plate boundary.
Viewed from a position above the north pole of the Sun, the direction of the motion of the planets in their orbits is
counterclockwise.
Where did the majority of the large amount of carbon dioxide (CO2) from the second major atmosphere to form on the early Earth end up?
dissolved in the oceans and, via the shells of living creatures, in the limestone of many mountain ranges
Accretion is the process by which
dust grains and ice crystals coalesce to form planetesimals.
Earth's magnetic field is most probably generated by
electric currents in Earth's electricity-conducting molten core..
Fusion is the process by which
elements are transformed into heavier elements by nuclear reactions.
What is believed to be the composition of Earth's core?
essentially pure iron
Earth has an average density that is approximately
five times that of water.
What is pressure?
force divided by the area over which the force acts
What is the basic structure of Earth's atmosphere?
four layers of alternating temperature profiles: temperature decreasing, then increasing, then decreasing, then increasing with altitude
What are the main characteristics of our solar system?
four small planets close to the Sun and four large planets far from the Sun
Most meteoroids are
fragments of asteroids.
The highest tides on Earth's oceans occur at
full or new Moon.
What is a proplyd?
protoplanetary disk, such as those observed around some stars in the Orion nebula
What is the Kuiper belt?
relatively flat distribution of objects in the plane of the ecliptic, extending from around the orbit of Pluto out to about 50 AU from the Sun
The most probable process for the formation or acquisition of the planets of the Sun is the
relatively slow growth of smaller objects by collisions and mutual gravitational attraction.
What process heated the early solar nebula as it slowly condensed toward a central protosun?
release of heat by collisions of particles as they gained kinetic energy in falling toward the center of the nebula
What is a planetary nebula?
result of a relatively gentle stellar outburst in which matter is ejected into space
The composition of a typical asteroid is
rock and metal.
The asteroid belt is made up of
rocky bodies with diameters from less than a kilometer to hundreds of kilometers.
What is the typical mass of the majority of extrasolar planets so far discovered?
roughly the mass of Jupiter up to a few times Jupiter's mass
What are the most common shapes of lunar craters, and why?
round because the incoming projectile vaporized and exploded to form the crater
The waves that geologists and geophysicists use to probe the inside of Earth are
seismic waves
A rille is a
shallow winding valley on the Moon.
To what does planetary differentiation refer?
sinking of heavier elements toward the center of a planet and the floating of lighter elements toward the surface
The overall shape of the orbits of most of the planets in the solar system is
slightly elliptical, but nearly circular.
The early phases of planetary formation into protoplanets were characterized by the
slow accretion of small particles by gravitational attraction and collision.
What is the basic structure of Earth's interior?
solid iron inner core, molten iron outer core, rocky mantle, lighter rocky crust