Astronomy Ch. 2 – Flashcards

backward, westward loop traced out by a planet with respect to the fixed stars

construct of the geocentric model of the solar system which was needed to explain observed planetary motions. a large circle encircling Earth, on which an epicycle moves

model of the solar system that holds that Earth is at the center of the universe and all other bodies are in orbit around it

geocentric solar system model, developed by the second-century astronomer Claudius Ptolemy. It predicted with great accuracy the positions of the then known planets

model of the solar system that is centered on the Sun, with Earth in motion

small shift in the observed direction to a star, caused by Earth's motion perpendicular to the line of sight

three laws derived by Kepler describing the motion of the planets around the Sun

geometric figure resembling an elongated circle. characterized by its degree of flatness, or eccentricity, and the length of its long axis.

one of two special points within an ellipse, whose separation from each other indicates the eccentricity.

one-half of the major axis of an ellipse. way in which the size of an ellipse is usually quantified

measure of the flatness of an ellipse, equal to the distance between the two foci divided by the length of the major axis

time needed for an orbiting body to complete one revolution about another body

average distance of Earth from the Sun.

acronym for radio detection and ranging

basic laws of motion, postulated by Newton, which are sufficient to explain and quantify virtually all of the complex dynamical behavior found on Earth and elsewhere in the universe

gravitational force exerted on you by Earth

action on an object that causes its momentum to change

tendency of an object to continue moving at the same speed and in the same direction unless acted upon by a force

a measure of the total amount of matter contained within an object

displacement (distance plus direction) per unit time

rate of change of velocity of a moving object

attractive effect that any massive object has an all other massive objects.

force exerted on one body by another due to the effect of gravity. directly proportional to the masses of both bodies involved and inversely proportional to the square of the distance between them

law that a field follows if its strength decreases with the square of the distance.

the "average" position in space of a collection of massive bodies, weighted by their masses.

speed necessary for one object to escape the gravitational pull of another.

an orbit which does not stay in a specific region of space, but where an object escapes the gravitational field of another.

Planets near opposition (a) rise in the east; (b) rise in the west; (c) do not rise or set; (d) have larger deferents

A major flaw in Copernicus's model was that it still had (a) the Sun at the center; (b) Earth at the center; (c) retrograde loops; (d) circular orbits

As shown in Figure 2.12 ("Venus Phases"), Galileo's observations of Venus demonstrated that Venus must be (a) orbiting Earth; (b) orbiting the Sun; (c) about the same diameter as Earth; (d) similar to the Moon

An accurate sketch of Jupiter's orbit around the Sun would show (a) the Sun far off center; (b) an oval twice as long as it is wide; (c) a nearly perfect circle; (d) phases

A calculation of how long it takes a planet to orbit the Sun would be most closely related to Keptler's (a) first law of orbital shapes; (b) second law of orbital speeds; (c) third law of planetary distances; (d) first law of inertia

An asteroid with an orbit lying entirely inside Earth's (a) has an orbital semimajor of less than 1 AU; (b) has a longer orbital period than Earth's; (c) moves more slowly than Earth; (d) must have a highly eccentric orbit

If Earth's orbit around the Sun were twice as large as it is now, the orbit would take (a) less than twice as long; (b) two times longer; (c) more than two times longer to traverse

Figure 2.21 ("Gravity"), showing the motion of a ball near Earth's surface, depicts how gravity (a) increases with altitude; (b) causes the ball to accelerate downward; (c) causes the ball to accelerate upward; (d) has no effect on the ball

If the Sun and its mass were suddenly to disappear, Earth would (a) continue in its current orbit; (b) suddenly change its orbital speed; (c) fly off into space; (d) stop spinning

Figure 2.25 ("Orbits"), shows the orbits of two stars of unequal masses. If one star has twice the mass of the other, then the more massive star (a) moves more slowly than; (b) mores more rapidly than; (c) has half the gravity of; (d) has twice the eccentricity of the less massive star

the angular diameter of an object

epicycles were used in Ptolemy's model to explain

How did the geocentric model account for day and night on Earth?

The heliocentric model assumes

Which of Gelilei's initial observations was most challenging to established geocentric beliefs?

Copernicus' heliocentric model was flawed because

Kepler's third law related a planet's distance from the Sun to its orbital

Who published the first astronomical observations with a telescope?

Who postulated three empirical laws of planetary motion?

Newton's laws of gravity states that the force between two objects

During the Dark Ages (roughly from the 5th to the 10th century A.D.), turmoil in Europe largely halted the progress of Western science. Which culture provided the vital link between the astronomy of ancient Greece and that of medieval Europe during this time? (a) South American (b) Chinese (c) Muslim (d) North American

Was it possible for the geocentric system of Ptolemy to explain the observed retrograde motion of the planets? (a) Yes, assuming that some planets orbited the Sun whereas others orbited Earth (b) No, because it was not able to predict retrograde motion (c) No, because it was not in use long enough to make such predictions (d) No, because observations of this retrograde motion were not known to the ancients. (e) Yes, through a system of epicycles and deferents

An accurate sketch of Jupiter's orbit around the Sun would show (a) a nearly perfect circle. (b) phases. (c) the Sun far off center. (d) an oval twice as long as it is wide.

A calculation of how long it takes a planet to orbit the Sun would be most closely related to Kepler's (a) first law of orbital shapes. (b) second law of orbital speeds. (c) first law of inertia. (d) third law of planetary distances.

If Earth's orbit around the Sun were twice as large as it is now, the orbit would take (a) less than twice as long. (b) two times longer. (c) more than two times longer to traverse.

Kepler's third law is best expressed as ________. (a) P 2 ~ a 3 (b) P ~ a (c) P 3 ~ a 2 (d) P ~ a 2

Earth is located at one _______ of the Moon's orbit

According to Kepler's second law, Jupiter will be traveling most slowly around the Sun when at ___________

Earth orbit in the shape of a/an _______ around the Sun

The mathematical form of Kepler's third law measures the period in years and the ________________ in astronomical units (AU).

According to Kepler's second law, Pluto will be traveling fastest around the Sun when at ___________

The extent to which Mars' orbit differs from a perfect circle is called its __________

What would happen to the orbits of each of the planets if the force of gravity was suddenly "turned off"? (a) Each would fall into the Sun. (b) Nothing; each would continue to orbit the Sun. (c) Each would slowly spiral away from the Sun. (d) Each would move in the opposite direction from the Sun. (e) Each would move off in a different straight line.

Two otherwise isolated bodies of equal mass will orbit in which of the following configurations as viewed from a fixed distant point? (a) They would both orbit in concentric ellipses about a central point. (b) They would orbit each other in identical but oppositely directed ellipses that share a common focus. (c) One would orbit in a large elliptical path around the other, which would stay fixed. (d) They would oscillate back and forth along a straight line connecting their centers. (e) One will orbit in a circular path around the other, which would stay fixed.

According to Newton, planets orbit in ellipses with what at the two foci? (a) The Sun and nothing (b) The Sun and the center of mass (c) The planet and its moon (d) The center of mass and nothing