Astronomy Chapter 3

Geocentric

A model of the universe in which Earth is at the center of the revolving planets and stars.

Heliocentric

A model of the solar system in which Earth and the other planets revolve around the sun.

Ellipse

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

Core

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

Sunspot

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

Terrestrial Planets

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

Greenhouse Effect

The trapping of heat by a planet's atmosphere.

Gas Giants

The name often given to the first two outer planets: Jupiter, Saturn

Ring

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

Comet

A loose collection of ice, dust, and small rocky particles, typically with a long, narrow orbit.

Coma

The fuzzy outer layer of a comet.

Nucleus

The solid inner core of a comet.

Kuiper Belt

A doughnut-shaped region that stretches from around Pluto's orbit to about 100 times Earth's distance from the sun.

Oort Cloud

A spherical region of comets that surrounds the solar system.

Asteroids

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

Asteroid Belt

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

Meteoroid

A chunk of rock or dust in space.

Meteor

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

Meteorite

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

Extraterrestrial Life

Life that exists other than that on Earth.

Ice Giants

The name often given to the second two outer planets: Uranus, Neptune