# A B C D E F G H I J K L M N O P Q R S T U V W X Y Z
G
galaxy: A cluster of stars. Our galaxy is called the ‘Milky Way’.
galvanic cell: An electrochemical cell.
gamma radiation: High-energy electromagnetic radiation that is emitted from the Sun as well as from radioactive materials.
gas: A state of matter where atoms or molecules are free to move. A gas fills the container that it occupies.
generator: A device that converts kinetic energy in the turning of a coil in a magnetic field into electrical energy.
geology: The science concerned with the study of Earth, including Earth’s materials (minerals and rocks), surface, internal processes and history.
geosynchronous orbit: An orbit where a satellite remains above the same position on Earth.
giant planets: Jupiter, Saturn, Uranus and Neptune.
glacier: A mass of moving ice on land.
global positioning system (GPS): A system of satellites that can tell a person their exact latitude, longitude and altitude (distance above Earth’s surface).
globular cluster: A spherically symmetrical collection of stars that share the same origin.
gravitational field: A region in space that moves particles of matter. Objects create a gravitational field around them.
gravitational force: A field force induced on an object that has mass.
gravitational potential energy: A potential energy associated with an object’s position in relation to another large object. For example, a 1 kg brick has more gravitational potential energy if it is 2 m off the ground than if it is 1 m off the ground. The greater the separation of the two pieces, the greater the gravitational potential energy.
greenhouse effect: A naturally occurring phenomenon where infra-red radiation is absorbed by the atmosphere and re-radiated back to Earth. This effect is responsible for keeping Earth warm.
greenhouse gas: A gas that absorbs infra-red radiation and contributes to the enhanced greenhouse effect.
Gregorian calendar: The calendar in current use, with normal years that are 365 days long, with leap years every fourth year except for centenary years that are not divisible by 400.
group: A vertical column in the periodic table.