Chapter 2

Question 1

Heliocentric

Answer 1

sun-centered model for the universe

Question 2

Magnitude System

Answer 2

system devised by Hipparchus for describing brightness of stars

Question 3

Prograde motion

Answer 3

eastward motion

Question 4

Geocentric

Answer 4

Earth centered model for the universe

Question 5

Epicycle

Answer 5

the circle path a planet travels around

Question 6

Deferent

Answer 6

the larger circle which the epicycle moves at a constant speed around

Question 7

Parallax

Answer 7

the shift in apparent position of an object when seen from two different locations

Question 8

geocentric parallax

Answer 8

the shift in apparent position of a relatively nearby object

Question 9

Heliocentric parallax

Answer 9

the shift in apparent position of a relatively nearby star when seen from two different points on the Earth’s orbit

Question 10

Inferior Planets

Answer 10

those with orbits smaller than the Earth’s orbit (Mercury, Venus)

Question 11

Superior Planets

Answer 11

those with orbits larger than the Earth’s orbit.

Question 12

Opposition

Answer 12

occurs when the Earth lies between the Sun and the superior planet. The Sun and planet are 180 degrees apart

Question 13

Conjunction

Answer 13

occurs when the Sun and the superior planet are 0 degrees apart as seen from the Earth

Question 14

Quadrature

Answer 14

occurs when the Sun and the superior planet are 90 degrees apart as seen from the Earth, can be either eastern or western

Question 15

Inferior conjunction

Answer 15

occurs when the inferior planet lies between the Earth and the Sun

Question 16

Superior conjunction

Answer 16

occurs when the Sun lies between the Earth and the inferior planet

Question 17

elongation

Answer 17

the angle in which the planet is separated from the Sun on the celestial sphere

Question 18

Synodic period

Answer 18

time interval which can be found by measuring the time elapsed between either successive superior conjunctions or successive inferior conjunctions

Question 19

Sidereal period

Answer 19

the time it takes the planet to complete one full circuit of the sky relative to the fixed stars.

Question 20

Greatest elongation

Answer 20

the maximum angular separation between the planet and Sun as seen from the Earth

Question 21

Astronomical Unit

Answer 21

average distance from the Earth to the Sun

Question 22

Kepler’s first law

Answer 22

Planets travel on elliptical orbits with the Sun at one focus

Question 23

major axis

Answer 23

the longest distance across the ellipse

Question 24

minor axis

Answer 24

the shortest distance across the ellipse

Question 25

eccentricity

Answer 25

the distance between the foci divided by the length of the major axis, if the foci coincide then the ellipse is a circle, e = 0

Question 26

Kepler’s second law

Answer 26

A line drawn from the Sun to a planet sweeps out equal areas in equal time intervals

Question 27

perihelion

Answer 27

the point on a planets orbit closest to the Sun, (moves rapidly)

Question 28

aphelion

Answer 28

the point farthest from the Sun, (least rapidly)

Question 29

Kepler’s third law

Answer 29

The squares of the sidereal orbital periods of the planets are proportional to the cubes of the semi-major axis of their orbits.

Question 30

aberration of starlight

Answer 30

an effect that causes the apparent positions of stars on the celestial sphere to be deflected in the direction of the observer’s motion.

Question 31

parsec

Answer 31

the distance at which a star has a parallax of exactly 1 arcsecond