Astronomy 129 Test #2 (Ch.4/7)
Newton's second law of motion states that a
body acted on by a force will accelerate constantly while the force is applied.
When Jupiter is at opposition, it rises at
sunset.
The semimajor axis of an ellipse is
the distance from the center of the ellipse to one end along the largest diameter of the ellipse.
Suppose an asteroid is discovered in an elliptical orbit with a period of exactly one year and at perihelion it is 0.5 AU from the Sun. Using Kepler's third law, how far from the Sun is this asteroid when at aphelion? (Drawing a diagram of the orbit, including the Sun, will help.)
1.5 AU
Which of the following statements is true,according to Kepler's third law?
The larger the orbit,the longer it takes for the planet to complete one revolution.
In which direction is Venus moving when it is at greatest elongation?
directly toward or away from Earth
The concept called Occam's Razor tells us that
when two theories describe the same phenomena equally accurately,choose the simpler theory.
Planets and satellites with a large amount of surface cratering generally havein significant atmospheres. Why are these two conditions correlated?
A large amount of cratering implies a small size,and this,in turn,implies a low escape speed.
What is the basic difference between comets and asteroids?
Comets are mostly composed of ices,while asteroids are mainly composed of rocks.
The law of gravitation expounded by Newton for the force F between two objects of masses M and m with separation (between centers) of R is given, with G being a constant,
F=GMm/R2
The Ptolemaic model of the universe included each of the following features,except one. Which one is the exception?
The apparent daily motion of the stars is due to the rotation of Earth.
A laboratory on the surface of the Earth makes a spectrum of radiation that originates at the Sun and reflects off a celestial body with an atmosphere such as Saturn's large satellite Titan. Which one of the following statements about the resulting spectrum is correct?
The atmosphere of the body can contribute sharp absorption lines to the spectrum.
Which one of the following statements describes the Newtonian understanding of the mechanics of the solar system?
The natural motion of the planets is motion in a straight line. They are prevented from straight line motion by the gravitational force of the Sun.
Which of the following statements correctly states the significance of Galileo's observation that Venus shows phases?
The phases were correlated with angular size in a way that supported the heliocentric theory.
What is the difference between the synodic and sidereal periods of a planet?
The synodic period refers to the planet's period with respect to Earth's motion, while the sidereal period is the true period with respect to the background stars.
The craters on the Moon are all nearly circular. Why is this?
Theobjectsthatproducedtheimpactcraterscameinatavarietyofangles,butthe craters were actually made by the shock waves generated by impact—and this results in circular craters.
Why were Newton's three laws so important to astronomy?
They showed that planets can move around the Sun by themselves forever,without coming to rest.
Which of the following statements is a correct version of Newton's third law?
When ever object Aexerts a force on some other object B,B must exert a force of equal magnitude on A in the opposite direction.
In Ptolemy's description of the solar system, the deferent is
a circular path (aroundEarth) along which the center of a planet's epicycle moves.
Based on its mean density, Pluto appears to be composed of
a mixture of rock and ice.
When observing planetary motions from Earth,the phrase"retrograde motion"refers to
a slow westward motion of the planet from night to night against the back ground stars.
In the geocentric model for the solar system developed by Ptolemy,to what does the word "epicycle" refer?
a small circle around which a planet moves while the center of this circle moves around Earth
The reason why Copernicus' heliocentric theory eventually came to be regarded as preferable to the geocentric theory of Ptolemy is that the heliocentric theory
accounted for the same observed motions of the planets as the geocentric theory but did so in a much simpler way.
We have discovered moons around
all the planets except those nearer to the Sun than Earth is.
If an object's orbit around the Sun has an eccentricity of 0.1,then the orbit is
almost circular.
If an object's orbit around the Sun has an eccentricity of 0.8,then the orbit is
along,thin ellipse.
An asteroid orbits the Sun in a circle with a sidereal period of 11.9years.Compare this with the orbital characteristics of the planets. At what equivalent distance will this asteroid orbit the Sun?
at the same orbital distance as Jupiter
If the mass of the Sun were doubled,the gravitational force on Jupiter due to the Sun would
be twice its present value.
If Halley's Comet has an elliptical orbit with a semi major axis of 17.5AU,approximately how far out into the planetary system does it reach at its furthest point (aphelion)? (Assume that perihelion distance from the Sun is negligible; be careful. The question needs some thought.)
between the orbits of Neptune and Pluto
The phenomenon of parallax is the
change in apparent position of a nearby object as the observer moves.
Galileo's early observations of the sky with his newly made telescope included the
fact that Venus showed phases similar to those of the Moon.
A major theme of Ancient Greek philosophy was that stars and planets in the sky
followed patterns that could be described logically.
What did Galileo see when he observed Jupiter through his telescope?
four satellites(moons)orbiting Jupiter
The main characteristics of our solar system are
four small planets close to the Sun and four large planets far from the Sun.
How will the illuminated side of Venus appear to us when it is at its greatest eastern elongation?
half-illuminated or quarter-phase
A body whose velocity is constant
has zero acceleration.
According to Newton's first law
if no force is acting on an object,then the object's speed and direction of travel will both be constant.
In which direction would Earth move if the Sun's gravitational force were suddenly removed from it?
in a straight line along at angent to its circular orbit
In the geocentric model of the solar system developed by Ptolemy,planets move
in circular epicycles while the centers of the epicycles move in circular orbits around Earth.
Newton's second law states that acceleration produced by a force is
inversely proportional to the mass on which the force acts.
When an object moves uniformly at a constant speed in a circle,the acceleration of the object is always
inward,toward the center of the circle.
In Newton's law of universa lgravitation,F=GMm/R2,which defines the force between Earth with mass M and an orbiting satellite of mass m at a distance R from Earth, G
is a constant,through out all measured space and time.
Kepler's second law states that a planet moves fastest when it
is closest to the Sun.
When Venus is at superior conjunction
it is at its greatest distance from Earth.
When Venus is at inferior conjunction,
it is at its smallest distance from Earth.
Where and when would Venus be seen from Earth when it is at greatest eastern elongation?
just after sunset, in the west
In the heliocentric model of the solar system,which one of the following phases of Venus should not be visible from Earth?
none of these They are all visible.
The mass of a planet is determined primarily by what method?
observation of its gravitational influence on an orbiting moon
To specify an object's speed, we need to specify
only how fast it is moving.
The primary purpose of describing planetary orbits in terms of epicycles and deferents was to account for the
pattern of direct and retrograde motion of a planet as it moved slowly against the background of stars.
What did Galileo see when he observed Venus through his telescope?
phases like those of the Moon
The greatest inaccuracy in Copernicus' theory of the solar system was that he
placed the planets in circular orbits.
Tycho Brahe demonstrated that the supernova of 1572 was not a nearby (close to Earth) event by
proving that it did not show parallax over the course of one night.
The first major astronomical prediction of Newton's theory of gravitation to be confirmed
return of Halley's comet.
A typical asteroid is made of
rock and metal.
The asteroid belt is made up of
rocky bodies from a few meters to tens of kilometers in diameter.
Orbital eccentricity is a number that describes the
shape of the orbital ellipse.
Kepler's second law states that a line joining a planet to the Sun
sweeps out equal areas in equal times.
Kepler's first law states that the orbit of a planet about
the Sun is an ellipse with the Sun at one focus.
A general summary of the planets in the solar system is that
the planets are remarkably different in size,magnetic field strength,and magnetic field generation method.
To which point in a planetary orbit does the word "perihelion"refer?
the point closest to the Sun
To which point in a planetary orbit does the word"aphelion"refer?
the point farthest from the Sun
An oxygen(O2) molecule has twice the mass of a methane(CH4)molecule.In a planet's atmosphere at some particular temperature, the average kinetic energy of an oxygen molecule is
the same as that of a methane molecule(i.e.,all molecules have the same average kinetic energy).
Careful description of the velocity of a moving object at a particular time requires that one define
the speed and the direction of the moving object.
Kepler's third law states that
the square of the orbital period is directly proportional to the cube of its mean distance from the Sun.
Kepler's third law in general applies
to all situations where two objects orbit each other solely under the influence of their mutual gravitational attraction.
A person standing on a bathroom scale sees a reading on the scale of 148pounds.This person is acted on by
two forces of equal size acting in opposite directions.
The discovery of nitrogen gas(N2)in the atmosphere of Titan was made by
ultraviolet spectroscopy from Earth.
Acceleration of a moving body is defined as the rate of change of
velocity with time.
Planets move past the background stars as seen by someone on Earth.What is the normal direction of this motion?
west to east because of the motion of the planet along its orbit
The average number of natural satellites(moons)per planet for the terrestrial planets is
less than one.
Tycho Brahe
made accurate measurements of planetary positions,which Kepler later used to find the shapes of planetary orbits.
The smallest terrestrial planet is
Mercury.
What was the most important difference in development between Isaac Newton's theory of planetary motion and that of Johannes Kepler?
Newton developed his theory from basic physical assumptions, whereas Kepler simply adjusted his theory to fit the data.
The ancient Greek thinker whose model of the universe came to dominate the medieval world was
Ptolemy
The Kepler model of the solar system is
Sun-centered,with elliptical planetary orbits.
The planet with the highest mean density is
Earth.
In order of increasing density,the Jovian planets are
Saturn, Uranus, Jupiter, Neptune.
The early Copernican system for planetary motions is
Sun-centered,with planets moving in perfect circles around the Sun.
If Earth were to be moved to a distance of 10AU from the Sun,how much stronger or weaker would be the Sun's gravitational force on Earth?
100times weaker
Suppose that a planet of 10 times the mass of Earth were orbiting the Sun at the same distance as Earth (1 AU). The gravitational force on this planet due to the Sun would be
10times that on Earth due to the Sun.
Halley's Comet returns to the Sun's vicinity every 76 years in an elliptical orbit.(SeeFig.4- 23, Freedman and Kaufmann, Universe, 8th ed.) What is the semimajor axis of this orbit?
17.5 AU
An imaginary planet is orbiting the Sun in a circle at precisely the same average orbital distance as Earth (i.e., one AU). What is its sidereal period?
1year
If a new planet (tentatively predicted to exist on the basis of perturbations in the orbits of Uranus and Neptune) were to be discovered with a sidereal period of 200 years, what would be the radius of its orbit (assumed to be circular)?
34.2 AU
Ptolemy's model for the solar system was
Earth-centered,with epicyclic planetary orbits.
Copernicus used the fact that Mars can sometimes be seen high in our sky at midnight to conclude that
Earth can come between Mars and the Sun.
Retrograde motion of a planet when viewed from Earth is caused by the fact that the
Earth is moving.
The largest of the terrestrial planets is
Earth.
Which one of the following statements about Copernicus' system of planetary motion is correct?
It used uniform circular motion.
In our solar system,which of the following planets is not a member of the terrestrial group?
Jupiter
In general,large bodies in the solar system show less evidence of cratering than do small bodies. Why should we expect this correlation?
Largebodiescoolmoreslowlyandaremorelikelytoretaininternalheatandbe geologically active, capable of resurfacing the planet and obliterating craters.
In our solar system,which of the following planets is not a member of the Jovian group?
Mars
Before the invention of the telescope,the known planets were
Mercury, Venus, Mars, Jupiter, and Saturn.
The correct order of"appearance"of the following"actors"on the"stage"of scientific discovery is
Ptolemy,Copernicus,Kepler,Newton,Einstein.