This is the glossay for Beyond our Horizons. It will give you definitions of words that pertain to space, but might be unfamiliar to you. You can look up the word here or, if it is highlighted, click on it in a document. The link will take you directly to the right word.

     Acceleration: n, The rate of change of velocity with respect to a change in time.

     Core: n, The innermost layer inside of a heavenly body, or planet.

     Gas Giants: n, The main gaseous planets of Jupiter, Saturn, Uranus, and Neptune. These outer planets have huge diameters, but no real solid surfaces. The atmosphere is made up of different gases ranging from hydrogen to methane.

     Geocentric: Theory of the solar system proposed by early Greek philosophers in which the earth is the center of the universe. It was suggested that all bodies orbited our planet.

     Heliocentric: Theory proposed by Polish astronomer Nicolaus Copernicus in which the sun is the central body in our solar system. It was suggested and later proven that all planets orbit around the sun.

     Orbit: n, The path taken by a heavenly body around a more massive body.

     Photons: n, Small particles that make up electromagnetic radiation. They carry varying amounts of energy and travel at the speed of light (3 x 10⁸ m/s).

     Photosphere: n, The visible outer layer of the sun.

     Plasma: n, A gas made up of electrons and ions, called the fourth state of matter. Plasma occurs when temperature is too high for whole atoms to exist.

     Plate Tectonics: n, Theory that the crust of Earth is covered by a number of plates floating independently on the hot mantle of the planet.

     Prominence: n, A huge cloud of hot solar gas emanating from the photosphere and held in place above the surface of the sun by magnetic fields.

     Silicate: n, Minerals containing silicon and oxygen, usually combined with one or more metals. Most rocks are silicates.

     Solar Wind: n, A stream of charged particles that emerge from the Sun.

     Speed: n, The distance traveled by a body divided by the time of travel.

     Velocity: n, The speed and direction of a body in motion. Velocity is a vector quantity.