Chapter 2

Geosynchronous satellites orbit at about four Earth radii, where the Earth's gravitational pull is:

1/16 g.

How much stronger is the gravitational pull of the Sun on Earth, at 1 AU, than it is on Saturn at 10 AU?

100X

Compared to orbital velocity, escape velocity is about:

40% more.

Kepler's second law implies what about planetary motion?

A planet moves faster when it is closer to the Sun.

The force of gravity varies with the:

A. product of the two masses. C. inverse square of the distance separating the two bodies.

Which of these was a contribution of Newton to astronomy?

All of the Above A. His differential calculus lets us calculate planetary motions more accurately. B. The Sun's gravity is greatest on a planet at perihelion, so the planet must speed up. C. Artificial satellites could be put into orbit about the Earth. D. The Moon pulls as strongly on us as we do on it.

Which of the following is a contribution to astronomy made by Galileo?

All of the above. A. Venus appears almost fully lit when it lies on the far side of the Sun. B. The Moon has craters, mountain, valleys, and dark flat areas on its surface. C. Jupiter has four moons orbiting it. D. The astronomical telescope can show us far more detail than the eye can.

The heliocentric model was actually first proposed by:

Aristarchus.

How does Newton's Universal Law of Gravitation explain Kepler's laws?

C. Universal gravitation implies that the planets further from the Sun will move more slowly than the planets closer to the Sun (Kepler's third law). D. Universal gravitation implies that when a planet is closer to the Sun in its orbit, it will move faster than when it is farther from the Sun (Kepler's second law).

What does Kepler's third law imply about planetary motion?

Planets further from the Sun orbit at a slower speed than planets closer to the Sun.

Which of these was NOT seen telescopically by Galileo?

Stellar parallax

Which of the statements below is part of both the Ptolemaic and Copernican models?

The Moon orbits the Earth once a month.

Which of the following was NOT a contribution of Galileo to astronomy?

The changing appearance of Saturn's rings corresponds to our seasons.

According to Newton's Law of Universal Gravitation, if the Moon were three times further from Earth, the force by Earth on the Moon would:

decrease by a factor of 9.

Kepler's first law worked, where Copernicus' original heliocentric model failed, because Kepler described the orbits as:

elliptical, not circular.

Tycho Brahe's contribution to Kepler's Laws of Planetary Motion was:

his detailed and accurate observations of the planet's position.

The force of gravity between two objects:

increases with the masses of the bodies, but decreases with the square of the distances between them.

According to Copernicus, retrograde motion for Venus must occur around:

inferior conjunction, when it passes between us and the Sun.

The Ptolemaic model probably persisted for all these reasons EXCEPT:

it accounted well for Galileo's observations of the phase cycle of Venus.

Escape velocity is the speed required to:

overcome the gravitational pull of an object.

The place in a planet's orbit that is closest to the Sun is called:

perihelion.

According to Kepler's third law, the square of the planet's period in years is:

proportional to the cube of its semimajor axis in A.U.

A planet whose distance from the Sun is 3 A.U. would have an orbital period of how many Earth-years?

square root of 27

Jupiter lies about 5 A.U. from the Sun, so at its distance:

the Sun's gravity is 25 times weaker than its pull on the Earth.

The Law of Universal Gravitation was developed by:

Newton.

Which concept was NOT a part of Kepler's Laws of Planetary Motion?

Epicycles are needed to explain the varying brightness of the planets.

If the mass of a body were doubled, its gravity would become 4 times stronger.

False

Which was a contribution to astronomy made by Copernicus?

He laid out the order and relative motion of the known solar system.

What contribution to astronomy was made by Tycho Brahe?

His observations of planetary motion with great accuracy proved circular orbits could not work.

A fatal flaw with Ptolemy's model is its inability to predict the observed phases of:

Mercury and Venus

Which of these was NOT a part of the original Copernican model?

Mercury speeds up at perihelion, and slows down at aphelion.

Upon which point do Copernicus and Kepler disagree?

The orbits of the planets are ellipses, with one focus at the Sun.

A planet (or comet) will speed up as it approaches the Sun.

True

According to Newton's second law, if you double the force acting on a body, the acceleration will double.

True

Galileo's observations of the entire phase cycle of Venus proved that Ptolemy's epicycles could not be correct in keeping Venus between us and the Sun

True

Kepler determined the shape of each planet's orbit by triangulation from different points on Earth's orbit, using observations made at many different times of the year.

True

Like the Sun and the Moon, the planets appear to move from west to east from one day to the next.

True

Mercury, with a higher eccentricity orbit, should change its orbital speed more than do Venus or Earth.

True

Newton's Law of Gravity would explain why Saturn, so far from the Sun, moves so slowly across the sky.

True

Newton's modification of Kepler's Third Law lets us measure the mass of the Sun.

True

The orbits of most of the planets in our solar system have eccentricities close to zero.

True

Transits of Venus were critical in early determinations of the A.U.

True

When a planet retrogrades, it appears to move westward for weeks at a time.

True

Galileo found the rotation period of the Sun was approximately:

a month.

According to Copernicus, the retrograde motion for Mars must occur:

at opposition, when the Earth overtakes Mars and passes between Mars and the Sun.

If the distance between two asteroids is doubled, the gravitational force they exert on each other will:

be one fourth as great.

Which of these observations of Galileo refuted Ptolemy's epicycles?

the complete cycle of Venus' phases

The greatest contribution of the Greeks to modern thought was:

the development of scientific inquiry and model building.

Orbital speed is the speed with which a planet moves around the Sun. This speed is determined by

the mass of both the planet and the Sun and the distance between the two.

Which of these was NOT a telescopic discovery of Galileo?

the moons of Saturn

Given that the planet orbiting the nearby star 51 Pegasi is about 20X larger than the Earth, but 400X more massive, on that world you would weigh:

the same as you do here.

Combining Newton's and Kepler's laws, we can weigh the Sun, provided we know:

the size of the A.U. and exact length of the year.

It took two centuries for the Copernican model to replace the Ptolemaic model because:

there was no scientific evidence to support either model until Galileo made his observations.

During the eighteenth and nineteenth centuries, attempts to precisely measure the astronomical unit relied largely on rare:

transits of the inferior planets across the Sun.