Chapter 3

Question 1

Aphelion

Answer 1

The point at which an object orbiting the Sun is farthest from the Sun

Question 2

Copernican revolution

Answer 2

The dramatic change, initiated by Copernicus, that occurred when we learned that Earth is a planet orbiting the Sun rather than the center of the universe.

Question 3

Deferent

Answer 3

The large circle upon which a planet follows its circle-upon-circle path around Earth in the (Earth-centered) Ptolemaic model of the universe.

Question 4

Epicycle

Answer 4

The small circle upon which a planet moved while simultaneously going around a larger circle (the deferent) around Earth in the (Earth-centered) Ptolemaic model of the universe.

Question 5

Ellipse

Answer 5

A type of oval that happens to be the shape of bound orbits. An ellipse can be drawn by moving a pencil long a string whose ends are tied to two stacks; the locations of the tacks are the foci (singular, focus) of the ellipse.

Question 6

Eccentricity

Answer 6

A measure of how much an ellipse deviates from a perfect circle; defined as the center-to-focus distance divided by the length of the semimajor axis.

Question 7

Foci

Answer 7

Plural of focus

Question 8

Focus (of a lens or mirror)

Answer 8

The point at which rays of light that were initially parallel (such as those from a distant star) converge.

Question 9

Focus (of an ellipse)

Answer 9

One of two special points within an ellipse that lie along the major axis; these are the points around which we could stretch a pencil and string to draw an ellipse. When one object orbits a second object, the second object lies at one focus of the orbit.

Question 10

Geocentric universe (ancient belief in)

Answer 10

The idea that Earth is the center of the entire universe.

Question 11

Geocentric model

Answer 11

Any of the ancient Greek models that were used to predict planetary positions under the assumption that Earth lay in the center of the universe.

Question 12

Horoscope

Answer 12

A predictive chart made by an astrologer; in scientific studies, horoscopes have never been found to have any validity as predictive tools.

Question 13

Hypothesis

Answer 13

A tentative model proposed to explain some set of observed facts, but which has not yet been rigorously tested and confirmed.

Question 14

Kepler’s laws of planetary motion

Answer 14

Three laws discovered by Kepler that describe the motion of the planets around the Sun.

Question 15

Kepler’s first law

Answer 15

Law stating that the orbit of each planet about the Sun is an ellipse with the Sun at one focus.

Question 16

Perihelion

Answer 16

The point in a planet’s orbit at which it is closest to the Sun.

Question 17

Aphelion

Answer 17

The point in a planet’s orbit at which it is furthest from the Sun.

Question 18

Kepler’s second law

Answer 18

As a planet moves around its orbit, it sweeps out equal areas in equal times. This means the planet moves faster at its perihelion than at its aphelion.

Question 19

Kepler’s third law

Answer 19

More distant planets orbit the Sun at slower average speeds, obeying a precise mathematical relationship. The relationship is written: p2(squared) = a3(cubed)

Question 20

Occam’s razor

Answer 20

The idea that scientists would prefer the simpler of two models that agree well with observations.

Question 21

Pseudoscience

Answer 21

False science

Question 22

Paradigm

Answer 22

The general patterns of thought