Glossary
This Glossary was adopted from the Helios glossary (http://helios.gsfc.nasa.gov/glossary.html). Underlined words represent words that are defined in this Glossary.

Atmosphere The mixture of gases that surround an object in space, such as a planet, moon or star, held near it by gravity.

Atom A basic unit of matter. Every atom has a positively charged center called a nucleus that is surround by a number of negatively charged electrons.

Attract To draw to or toward itself.

Aurora (plural = aurorae) Light radiated by ions and atoms in Earth’s upper atmosphere, in the region of Earth’s poles. Aurora can be an extremely impressive spectacle. The Aurora australis, or “Southern Lights” occur near the South Pole while the Aurora borealis, or “Northern Lights” occur near the North Pole.

Boom A part of a spacecraft that is long and cylindrical to hold instruments far from the satellite bus when it is in space.

Cause Something that produces an effect.

Compass A device that determines the presence of a magnetic field and its direction.

Corona The outer part of the Sun’s “atmosphere.” In the outer region of the corona, particles travel away from the Sun and stretch far out into space. The corona can only be seen during total solar eclipses, appearing as a halo around the moon.

Coronal Mass Ejections (CMEs) Huge bursts of solar wind rising above the Sun’s corona. These are one of the biggest explosions in the Solar System.

Dipole Two electric charges or magnetic poles that have the same strength but are opposite in sign or polarity (North versus South) and are separated by a small distance.

Earth The third planet from the Sun on which we all live.

Eclipse The blocking of some or all of the light from one object by another.

Effect Something brought about by a cause; a result.

Electric charge A physical state based on the amount and location of electrons and protons in matter. Matter with more electrons than protons is negatively charged. Matter that attracts free electrons is positively charged.

Electric circuit A system that connects electrical components so that they will operate.

Electric current A flow of electric charge.

Electron The negatively charged part of an atom and one of the smallest particles in the universe. It orbits the atom’s nucleus. Electrons are very light compared to protons and neutrons.

Element A material consisting of atoms, all with the same atomic number. Approximately 90 different elements are known to exist in nature and several others have been created in nuclear reactions. For more information about the elements, see the Periodic Table of the Elements.

Experiment A test under controlled conditions that is made to determine how something in nature works.

Gas A low number of atoms or molecules in a relatively large volume of space so that their interaction is small.

Geographic North Pole The northern point on Earth around which Earth rotates.

Gravity A physical force that attracts objects to one another. This force is very weak and only objects made of a lot of protons and electrons will have enough gravity to affect other objects. For example Earth has enough atoms that its gravity holds us on this planet. But a teacher does not have enough atoms to attract a coffee mug with gravity.

Hydrogen The most common element in the universe. Each atom of hydrogen contains one proton and one electron.

Interplanetary Between the planets in our solar system.

Instrument An electrical and/or mechanical device that collects data as part of an experiment.

Ion An atom that carries a positive or negative electric charge as a result of having lost or gained one or more electrons.

Iron An element that has an un-paired electron making it able to align with a nearby magnetic field.

Magnet, solenoid A solenoid magnet is a coil of insulated wire, usually cylindrical in shape and with a length greater than its diameter. An electric current passing through the solenoid produces a magnetic field similar to that of a bar magnet.

Magnetic field A region of space near a magnetized body or electrical current where magnetic forces can be detected.

Magnetic field lines These lines are a way to show the structure of a magnetic field. A compass needle will always point along a field line. The lines are close together where the magnetic force is strong, and spread out where it is weak.

Magnetism (Electromagnetism) A physical property of an object that shows attraction for iron, as in a magnet. Electromagnetism acts between particles with an electric charge, such as electrons, protons, and ions. It is associated with moving electricity, and it creates fields of force.

Magnetometer An instrument that measures the magnitude (strength) and direction of a magnetic field.

Magnetosphere The region surrounding a planet where the planet’s magnetic field dominates.

Molecule Two or more atoms bound together. As an example, a molecule of water consists of two atoms of hydrogen and one of oxygen.

Neutron The part of an atom that has no charge. It is often part of the nucleus.

Nucleus (plural=nuclei) The small, massive center of an atom containing its protons and neutrons bound together by nuclear force, the strongest force known in nature.

Orbit The path a body takes around another object or point in space under the influence of various physical forces, including gravity.

Physics The science dealing with matter and energy and their interaction.

Planet A body that orbits a star such as the Sun.

Proton The positively charged part of an atom.

Satellite An object that revolves around a larger object. Planetary moons are natural satellites.

Satellite bus The body of a man-made satellite that the control functions of the satellite and most of the scientific instruments.

Solar Having to do with the Sun.

Solar wind Ions and electrons that come out of the Sun in all directions at very fast speeds.

Solar System The Sun and its associated planets and their moons, and all other objects that are held by the Sun’s gravity and orbit around it.

Space The area between all of the bodies in the universe. It is not empty! It contains magnetic fields, electromagnetic radiation (i.e. light), gases, dust and other particles.

Sun The star at the center of our solar system. It is made mostly of hydrogen and helium with a very small amount of heavier elements.