21st Century Astronomy Chapter 03

The planet Uranus will be observed in retrograde motion whenChoose one:A. Uranus is farthest from the Sun.B. Earth overtakes Uranus in its orbit.C. Uranus is closest to the Sun.D. Uranus overtakes Earth in its orbit.

B. Earth overtakes Uranus in its orbit.

Place the following in order from largest to smallest semimajor axis:

1. A planet with a period of 2 earth years 2. A planet with a period of 1 earth years 3. A planet with a period of .5 earth years 4. A planet with a period of 84 earth days

A net force must be acting when an object (select all that apply):Choose one or more:A.accelerates.B.changes speed and direction.C.changes direction but not speed.D.changes speed but not direction.

A.accelerates.B.changes speed and direction.C.changes direction but not speed.D.changes speed but not direction.

A net force must be acting when an objectChoose one or more:A.changes speed but not direction.B.changes both speed and direction.C.accelerates.D.changes direction but not speed.

A.changes speed but not direction.B.changes both speed and direction.C.accelerates.D.changes direction but not speed.

Which of Galileo's astronomical observations were best explained by a heliocentric model?Choose one or more:A.phases of VenusB.moons of JupiterC.sunspotsD.craters on the Moon

A.phases of Venus B.moons of Jupiter

Sort each scenario into the category indicating whether or not the car is accelerating.

Accelerating: slowing speed, increasing speed, constant speed while turning Not accelerating: constant speed

An empirical science is one that is based onChoose one:A. observed data.B. hypothesis. C. computer models.D. calculus.

A. observed data.

How did the ancients know the planets were different from the stars?Choose one:A. They saw that the planets move with respect to the stars over the course of many nights.B. The planets have a larger angular size in our sky than the stars.C. They observed moons orbiting around the planets.D. They noticed that the planets orbit the Sun, while the stars do not.

A. They saw that the planets move with respect to the stars over the course of many nights.

Suppose you read on the Web that a new planet has been found. Its average speed in its orbit is 33 kilometers per second (km/s). When it is closest to its star, it moves at 31 km/s, and when it is farthest from its star, it moves at 35 km/s. This story is in error becauseChoose one:A. planets stay at a constant distance from their stars; they don't move closer or farther away.B. Kepler's second law says the planet must move fastest when it is closest, notwhen it is farthest away.C. the average speed is too fast.D. Kepler's third law says the planet has to sweep out equal areas in equal times, sothe speed of the planet cannot change.E. using these numbers, the square of the orbital period will not be equal tothe cube of the semimajor axis.

B. Kepler's second law says the planet must move fastest when it is closest, notwhen it is farthest away.

Both Kepler's laws and Newton's laws tell us something about the motion of the planets, but there are fundamental differences between them. What are the differences? Select all of the true statements. Choose one or more:A.Kepler's discoveries built on the work of an earlier astronomer, while Newton's did not.B.Kepler defined laws based on one special case—the observed motions of planets in the Solar System, while Newton defined theoretical laws that describe the general behavior of all motions in the universe.C.Kepler reported how planets moved, and Newton explained why. D.Kepler's approach was empirical, while Newton's was theoretical.

B.Kepler defined laws based on one special case—the observed motions of planets in the Solar System, while Newton defined theoretical laws that describe the general behavior of all motions in the universe.C.Kepler reported how planets moved, and Newton explained why. D.Kepler's approach was empirical, while Newton's was theoretical.

Watch the AstroTour on Kepler's Laws and choose the statement below that directly follows from Kepler's second law of planetary motion.Choose one:A. The area swept out by the orbit of Jupiter in five days is the same as the area swept out by Mars in five days.B. Venus is traveling faster when it is at perihelion (the closest distance to the Sun) than when it is at aphelion (the farthest distance from the Sun). C. All the planets travel in elliptical orbits around the Sun.D. Mercury's year (the time it takes to orbit the Sun once) is shorter than Saturn's year.

B. Venus is traveling faster when it is at perihelion (the closest distance to the Sun) than when it is at aphelion (the farthest distance from the Sun).

Copernicus's model of the Solar System was superior to Ptolemy's because Choose one:A. it was more accurate.B. it had a mathematical basis that could be used to predict the positions of planets.C. it was simpler.D. it did not require epicycles.

B. it had a mathematical basis that could be used to predict the positions of planets.

Newton's second law of motion states thatChoose one:A. objects have inertia.B. the acceleration of an object is proportional to the net force acting on it.C. every action has an equal and opposite reaction.

B. the acceleration of an object is proportional to the net force acting on it.

Imagine a planet moving in a perfectly circular orbit around the Sun. Is this planet experiencing acceleration?Choose one:A. No. Its speed is not changing all the time.B. No. Planets do not experience accelerations.C. Yes. It is changing its direction of motion all the time.D. Yes. It is changing its speed all the time.

C. Yes. It is changing its direction of motion all the time.

To test Copernicus's model, Tycho took meticulous measurements of the positions of the planets, and he hired Kepler to interpret the data. Kepler found that the geocentric model did not accurately predict the planets' positions, but neither did Copernicus's heliocentric model. He found that Copernicus's insistence that the planets' orbits were perfectly circular was the problem. If the orbits were instead ellipses, then the heliocentric model would have been able to very accurately predict the positions of the planets. This is known as Kepler's first law of planetary motion. View the AstroTour animation on Kepler's Laws and then choose the statements below that are correct. Choose one or more:A.The Sun is located at one focus of a planet's elliptical orbit, and the planet is located at the other focus.B.The eccentricity of Mars's orbit is zero.C.Elliptical orbits cause a planet to sometimes be closer to and sometimes farther away from the Sun. D.Halley's Comet has a highly eccentric orbit. E.The Sun is located at the center of a planet's elliptical orbit.

C.Elliptical orbits cause a planet to sometimes be closer to and sometimes farther away from the Sun. D.Halley's Comet has a highly eccentric orbit.

Imagine you are walking along a forest path. Which of the following is not an action-reaction pair in this situation?Choose one:A. The gravitational force between you and Earth; the gravitational force between Earth and you.B. Your shoe pushes back on Earth; Earth pushes forward on your shoe.C. Your foot pushes back on the inside of your shoe; your shoe pushes forward on your foot.D. You push down on Earth; Earth pushes you forward.

D. You push down on Earth; Earth pushes you forward.

An inferior planet is one that isChoose one:A. larger than Earth.B. farther from the Sun than Earth is.C. smaller than Earth.D. closer to the Sun than Earth is.

D. closer to the Sun than Earth is.

When Earth catches up to a slower-moving outer planet and passes it in its orbit, in the same way that a faster runner overtakes a slower runner in an outside lane, the outer planet Choose one:A. slows down because it feels Earth's gravitational pull.B. decreases in brightness as it passes through Earth's shadow.C. moves into a more elliptical orbit.D. exhibits retrograde motion.

D. exhibits retrograde motion.

Kepler's second law says that Choose one:A. planetary orbits are ellipses with the Sun at one focus.B. for every action there is an equal and opposite reaction.C. the square of a planet's orbital period equals the cube of its semimajor axis.D. planets move fastest when they are closest to the Sun.

D. planets move fastest when they are closest to the Sun.

The time it takes for a planet to come back to the same position relative to the Sun is called its __________ period.Choose one:A. geocentric B. heliocentric C. sidereal D. synodic

D. synodic