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.
Astronomical Unit The average distance between the Earth and Sun, about 150 million kilometers
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 or auroras) 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.
Chromosphere The layer of the solar atmosphere that is located above the photosphere and beneath the corona. The chromosphere is hotter than the photosphere but not as hot as the corona.
Convection The organized flow of large groups of molecules based on their relative densities or temperatures. A hot fluid or gas will move upward, and a cooler liquid or gas will sink downward.
Convection Zone The solar layer just below the photosphere, in which plasmas circulate between the Sun's radiative zone and the solar atmosphere, carrying energy outward.
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 Loop A loop structure near the Sun's surface. Magnetic field lines emerging from the photosphere and returning to it in a region of opposite magnetic polarity organize the hot (one million degree Kelvin) plasma of the corona into these loop structures.
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.
Density The amount of mass or number of particles per unit volume. In c-g-s units mass density has units of gm cm-3. Number density has units cm-3 (particles per cubic centimeter).
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 relatively 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.
Electromagnetic Field The region in which electromagnetic radiation from a source exerts an influence on another object with or without there being contact between them.
Electromagnetic Radiation Form of radiant energy that travels through space at 300,000 km/s and propagates by the interplay of oscillating electric and magnetic fields. This radiation has a wavelength and a frequency. (See also Light)
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 surrounds 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.
Gamma Ray Extremely high-energy radiation observed during large, very energetic solar flares. Gamma rays are more energetic, and have shorter wavelengths than all other types of electromagnetic radiation.
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 where the axis, around which Earth rotates, intersects Earth's surface.
Granulation Appearance on the Sun’s photosphere of roughly circular regions on the Sun whose bright centers indicate hot gases rising to the surface, and whose dark edges indicate cooled gases that are descending towards the interior. Individual granules appear and disappear on time scales of about 5 minutes and are typically about 1000 km.
Gravity A physical force that attracts objects to one another. This force is very weak and only objects made of a lot of matter 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.
H-alpha Light emitted at a wavelength of 656.3 nanometers from an atomic transition in hydrogen. This wavelength is in the red portion of the visible spectrum and is emitted by plasma at about 10,000 K, mainly in the solar chromosphere.
Heat The transfer of thermal energy between two systems of particles that are at different temperatures.
Hydrogen The most common element in the universe. Each atom of hydrogen contains one proton and one electron.
Infrared The infrared includes electromagnetic radiation at wavelengths just beyond the visible spectrum. Infrared wavelengths are longer than visible radiation and shorter than radio radiation.
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.
Kinetic Energy The energy of motion, observable as the movement of an object, particle, or set of particles.
Light Form of radiant energy transmitted at a velocity of about 300,000 km/s by wavelike or vibrational motions in electromagnetic fields. (See also Electromagnetic Radiation)
Luminosity The amount of light energy output per unit time by an object.
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.
Magnetic Pole A location in a magnetic field where lines of force all converge.
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 the motion of charged particles.
Meteorite The remains of a meteoroid that plunges to the Earth’s surface. A meteorite is a stony or metallic mass of matter that did not completely vaporize when it entered the Earth’s atmosphere.
Meteoroid A small, rocky object left over from the formation of the Solar System moving through interplanetary space. A meteoroid produces a meteor when it enters the Earth’s atmosphere.
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 An electrically neutral elementary particle. It is often part of the nucleus of an atom and is 1839 times heavier than an electron.
Nuclear Fusion The joining of atomic nuclei under tremendous temperatures and pressures to create nuclei of heavier elements. In the Sun, four hydrogen nuclei are fused to create a single helium nucleus. Two of the hydrogen's protons become neutrons in the process.
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.
Photosphere The lowest layer of the solar atmosphere, where the Sun's visible spectrum of light (electromagnetic radiation) is released. It is the visible "surface" we see in white-light images of the Sun.
Physics The science dealing with matter and energy and their interaction.
Planet A body that orbits a star such as the Sun.
Plasma A gas of charged particles, such as electrons and ionized (charged) nuclei, often hydrogen nuclei (protons). This occurs when atoms of a gas are torn apart by high temperatures, pressures, and/or electromagnetic fields.
Potential Energy The energy associated with a configuration of particles, as distinct from their motions. In macroscopic systems, potential energy can be increased (for example) by stretching a spring or by lifting a mass against a gravitational force; in microscopic systems, potential energy can be increased (for example) by stretching a molecular bond or by separating molecules against an electromagnetic attraction.
Pressure Force applied over a surface.
Prominence A structure in the corona consisting of cool plasma supported by magnetic fields. In visible light, prominences are bright structures when seen over the solar limb, but appear dark when seen against the bright solar disk. Prominences seen on the disk are also known as filaments. Prominences may become parts of CME's if they lift off of the Sun.
Proton The positively charged part of an atom.
Radiative Zone Layer just outside the Sun's core, where energy is transported mostly in the form of radiation. This region, while too cool for fusion to occur, is still very dense and hot- about 4 million degrees Kelvin.
Radio A kind of electromagnetic radiation, like visible light, but with wavelengths far longer than the red or even the infrared portion of the spectrum.
Radioactive A substance is said to be radioactive if the atomic nuclei it contains exhibit spontaneous disintegration or decay by emission of particles, and/or electromagnetic radiation.
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 Cycle Regular increase and decrease of sunspots and other solar activity, such as solar flares and CMEs, which are thought to be physically related. Sunspots go through one cycle of activity in approximately 11 years. The Sun's magnetic polarity reverses between every cycle.
Solar Flare A sudden eruption in the vicinity of a sunspot, lasting minutes to hours, caused by the release of large amounts of magnetic energy in small volume above the solar surface.
Solar Wind Plasma 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 volume 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.
Star A huge ball of gas held together by gravity. The central core of a star is extremely hot and produces energy via nuclear fusion. Some of this energy is released as visible light, which makes the star glow. Stars come in different sizes, colors, and temperatures. Our Sun, the center of our Solar System, is a yellow star of average temperature and size.
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.
Sunspot A temporary concentration in the magnetic field on the Sun, where convection of hot matter from the Sun's interior is inhibited, resulting in a cooler, darker area on the photosphere of the Sun. The average sunspot is about the same diameter as Earth.
Temperature A measure of the average kinetic energy of a system of particles.
Thermal Energy The total kinetic energy due to disordered motions and vibrations of a system of microscopic particles such as molecules and atoms.
Ultraviolet Electromagnetic radiation at shorter wavelengths and higher energies than the violet part of visible light.
Visible Light Electromagnetic radiation (light) that is visible to the human eye. Visible light wavelengths are shorter than ultraviolet and longer than infrared.
X-ray Electromagnetic radiation of very short wavelength, and very high energy. X-rays have shorter wavelengths than ultraviolet light, but longer wavelengths than gamma rays.
