Chapter 12 The Solar System

Front 1

Revolution

Back 1

the movement of an object around another object.

Front 2

rotate

Back 2

The spinning motion of a planet on its axis.

Front 3

gravity

Back 3

The attractive force between objects; the force that moves objects downhill.

Front 4

geocentric

Back 4

Term describing a model of the universe in which Earth is at the center of the revolving planets and stars.

Front 5

heliocentric

Back 5

Term describing a model of the solar system in which Earth and the other planets revolve around the sun.

Front 6

ellipse

Back 6

An oval shape, which may be elongated or nearly circular; the shape of the planets’ orbits.

Front 7

solar system

Back 7

The system consisting of the sun and the planets and other objects that revolve around it.

Front 8

astronomical unit

Back 8

A unit of distance equal to the average distance between Earth and the sun, about 150 million kilometers.

Front 9

planet

Back 9

An object that orbits a star, is large enough to have become rounded by its own gravity, and has cleared the area of its orbit.

Front 10

dwarf planet

Back 10

An object that orbits the sun and is spherical, but has not cleared the area of its orbit.

Front 11

planetesimal

Back 11

One of the small asteroid-like bodies that formed the building blocks of the planets.

Front 12

core

Back 12

The central region of the sun, where nuclear fusion takes place.

Front 13

nuclear fusion

Back 13

The process in which two atomic nuclei combine to form a larger nucleus, forming a heavier element and releasing huge amounts of energy; the process by which energy is produced in stars.

Front 14

radiation zone

Back 14

A region of very tightly packed gas in the sun’s interior where energy is transferred mainly in the form of electromagnetic radiation.

Front 15

convection zone

Back 15

The outermost layer of the sun’s interior.

Front 16

photosphere

Back 16

The inner layer of the sun’s atmosphere that gives off its visible light; the sun’s surface.

Front 17

chromosphere

Back 17

The middle layer of the sun’s atmosphere.

Front 18

corona

Back 18

The outer layer of the sun’s atmosphere.

Front 19

solar wind

Back 19

A stream of electrically charged particles that emanate from the sun’s corona.

Front 20

sunspot

Back 20

A dark area of gas on the sun’s surface that is cooler than surrounding gases.

Front 21

prominence

Back 21

A huge, reddish loop of gas that protrudes from the sun’s surface, linking parts of sunspot regions.

Front 22

solar flare

Back 22

An eruption of gas from the sun’s surface that occurs when the loops in sunspot regions suddenly connect.

Front 23

terrestrial planet

Back 23

The name often given to the four inner planets: Mercury, Venus, Earth, and Mars.

Front 24

greenhouse effect

Back 24

The trapping of heat near a planet’s surface by certain gases in the planet’s atmosphere.

Front 25

gas giant

Back 25

The name often given to the outer planets: Jupiter, Saturn, Uranus, and Neptune.

Front 26

ring

Back 26

A thin disk of small ice and rock particles surrounding a planet.

Front 27

asteroid belt

Back 27

The region of the solar system between the orbits of Mars and Jupiter, where many asteroids are found.

Front 28

kuiper belt

Back 28

A region that stretches from beyond the orbit of Neptune to about 100 times Earth’s distance from the sun.

Front 29

oort cloud

Back 29

A spherical region of comets that surrounds the solar system.

Front 30

comet

Back 30

A loose collection of ice and dust that orbits the sun, typically in a long, narrow orbit.

Front 31

coma

Back 31

The fuzzy outer layer of a comet.

Front 32

nucleus

Back 32

The solid inner core of a comet.

Front 33

asteroid

Back 33

One of the rocky objects revolving around the sun that are too small and numerous to be considered planets.

Front 34

meteoroid

Back 34

A chunk of rock or dust in space, generally smaller than an asteroid.

Front 35

meteor

Back 35

A streak of light in the sky produced by the burning of a meteoroid in Earth’s atmosphere.

Front 36

meteorite

Back 36

A meteoroid that passes through the atmosphere and hits Earth’s surface.