Astronomy Exam Chp 3&4
Kepler's first law states that a planet moves around the Sun in a(n)
elliptical orbit, with the Sun at one focus
What fundamental belief about the universe, established by the Greeks and adopted by the early Christian church, was shattered by Galileo's observation of moons orbiting Jupiter?
everything in the universe orbits the Earth
When observing planetary motions from the Earth, the phrase direct motion refers to the
slow eastward motion of the planet from night to night compared to the background stars
keplers third law tells us that the
square of a planet's period in years is the same number as the cube of its semimajor axis in AU.
Kepler's second law states that a line joining a planet to the Sun
sweeps out equal areas in equal times
the tern retrograde motion for a planet refers to the
temporary reversal of the planet's normal west-to-east motion past the background stars as seen from the Earth.
the semi major axis of an ellipse is
the distance from the center of the ellipse to one end, along the largest diameter of the ellipse
Kepler's third law can be described in which of the following ways?
The larger the orbit of a planet, the longer the planet takes to complete one revolution
The major contribution of Tycho Brahe to the development of modern astronomy was
measuring planetary positions very accurately
in the geocentric model of the solar system, which one of the following phases of Venus should be visible from Earth?
new
he sidereal period of a planet is defined as the time between two successive
passages of the planet in front of a particular point in the sky (e.g., a star) as seen from the Sun
Kepler's third law, the harmonic law, provides a relationship between a planet's orbital
period and the length of the semimajor axis
To which point in a planetary orbit does the word perihelion refer?
point closest to the Sun
To which point in a planetary orbit does the word aphelion refer?
point furthest from the Sun
An apparent westward motion of a planet from night to night compared to the background stars (as viewed from the Earth) is referred to as
retrograde motion
What was the most important difference between the development of 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
What was the most important contribution of Newton to the development of astronomy?
Newton showed that astronomical phenomena can be explained using only basic physics and mathematics.
Why were Newton's three laws so important to astronomy?
Newton's laws showed that planets can move around the Sun by themselves forever, without coming to rest.
the time period between two successive passages of a planet past a particular star as seen from the Sun is its
sidereal period
A comet is observed to return to the vicinity of the Sun on a long elliptical orbit with a period of 31.7 years. What is the semimajor axis of the orbit?
10 AU
A diver weighing 138 pounds has just dived up and out from the high board and is doing a back flip before starting to descend toward the water. How much force does the diver exert on the Earth while doing the back flip?
138 pounds
Halley's Comet returns to the Sun's vicinity approximately every 76 years in an elliptical orbit. According to Kepler's third law, what is the semimajor axis of this orbit?
17.9 AU
If a planet were to exist in our solar system in a circular orbit with a radius of 3 AU, about how long would it take to orbit the Sun once?
5.2 years
The Sun exerts a gravitational pull on Earth. Why doesn't Earth fall into the Sun?
Earth is moving across the Earth-Sun direction, so Earth is pulled around in a circle.
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, by
F = GMm/R2.
the planets that were known before the telescope was invented were
Saturn, Venus, Mars, Mercury, and Jupiter
The Copernican system for planetary motions is
Sun-centered, with the planets moving in perfect circles around the Sun
Which of the following observations of the motions of the large moons of Jupiter did Galileo find most significant?
The moons farther from Jupiter had longer periods, just as Copernicus had discovered for the planets around the Sun.
Which of the following descriptions characterizes the Newtonian understanding of the mechanics of the solar system?
The natural motion of the planets is motion in a straight line. The planets are prevented from straight-line motion by the gravitational force of the Sun.
Which of the following sentences correctly states the significance of Galileo's observation that Jupiter has satellites (moons)?
The observation showed that Jupiter must be four times the size of the Earth (because Jupiter has four moons and the Earth has one).
What did Galileo NOT observe with his new telescope?
Uranus
If an object has an orbit around the Sun that has an eccentricity of 0.8, then the orbit is
a long, thin ellipse
from the earth, we observe occasional retrograde motion in the motion of
all the planets
If an object has an orbit around the Sun that has an eccentricity of 0.1, then the orbit is
almost circular, but not quite
an object orbiting the Sun in a circle can be said to be
always accelerating
According to Newton's second law of motion, an object acted on by a constant force
always moves with a constant acceleration.
At what point in a planetary orbit is the planet's speed the slowest?
at aphelion
When viewed from the Earth, the celestial sphere (the background of stars) moves east to west on a daily basis. This motion is caused by the
rotation of the earth on its axis
Nicolaus Copernicus was the first person to
develop a comprehensive model for a Sun-centered solar system
An apparent eastward motion of a planet from night to night compared to the background stars (as viewed from the Earth) is referred to as
direct motion
A significant contribution of Kepler to our understanding of the solar system was the
discovery that planetary orbits are not circular
Which of the following pairs of forces is an example of an action-reaction pair by Newton's third law?
for a dog pulling on its leash, the force of the dog on the leash and the force of the leash on the dog
newton's second law states that
force equals mass times acceleration
a body whose velocity is constant
has zero acceleration
according to Newton's first law
if no net force is acting on an object, then both the objects speed and direction of travel will be constant
In which direction would the Earth move if the Sun's gravitational force were suddenly removed from it?
in a straight line along a tangent to its circular orbit
Kepler's second law states that a planet moves fastest when it
is closest to the Sun
The eccentricity of a planet's orbit describes
its shape compared to that of a circle
The time period between two successive passages of a planet through the position of opposition is
its synodic
The distance from the perihelion point to the aphelion point of a planetary orbit is
the major axis
Why did Galileo's observations of moons orbiting Jupiter disagree with the theory of the universe accepted up to that time in history?
the moons did not orbit the Earth
Suppose two asteroids are located at the same distance from the Sun. One asteroid has twice the mass of the other. According to Newton's law of gravitation (and ignoring all forces except that from the Sun),
the more massive asteroid feels twice the force that the other does.
Galileo's early observations of the sky with his newly made telescope included the discovery of
the phases of Venus
The time interval between two successive repeated positions of a planet with respect to the Sun and the Earth in its orbit, such as conjunction to conjunction, is known as
the planet's synodic period
According to Newton's third law, if a force is acting on an object, then
there must be some other force acting on a different object, with the same magnitude but in the opposite direction
the acceleration of a moving body is defined as the rate of change of
velocity with time
the word planet is derived from a Greek term meaning
wanderer
In the simplified version of Kepler's third law, P2 = a3, the units of the orbital period P and the semimajor axis of the ellipse a must be, respectively,
years and astronomical units