A

Active region: An area of the solar atmosphere where the sun’s magnetic field is both concentrated and contorted. The contortion of the magnetic field results in the formation of dark areas such as sunspots and bright areas known as faculae . These regions also produce flares and plages . (TOP OF THE PAGE)   (CLOSE WINDOW)

Aurora: Luminous and colorful "curtains of light" typically seen in the night skies of the high northern and southern latitudes. During times of increased solar activity, they can be seen at much lower latitudes. The aurora is produced when electrons from the sun’s solar wind disturb the earth’s magnetic field and interact with molecules in the earth’s upper atmosphere. (TOP OF THE PAGE)   (CLOSE WINDOW)

Aurora Australis: The aurora in the southern hemisphere, also known as the southern lights. THE PAGE)   (CLOSE WINDOW)

Aurora Borealis: The aurora in the northern hemisphere, also known as the northern lights. (TOP OF THE PAGE)   (CLOSE WINDOW)

Auroral Oval: From space, the auroral zone looks like a donut of light hovering over the north and south poles. This auroral oval can easily be seen in satellite images, and its brightness and size changes with the level of solar activity. (TOP OF THE PAGE)   (CLOSE WINDOW)

C

Chromosphere: The layer of the solar atmosphere immediately above the visible surface of the sun with flame-like structures called "spicules." The chromosphere extends a few thousand kilometers above the sun’s surface.  (TOP OF THE PAGE)   (CLOSE WINDOW)

Corona: The outermost layer of the sun’s atmosphere, which extends more than two million kilometers above the sun’s visible surface. The appearance and shape of the corona varies with the sun’s activity cycle. The corona is most prominent when the number of sunspots reaches a maximum in the solar cycle. (TOP OF THE PAGE)   (CLOSE WINDOW)

Coronal mass ejection: Magnetic field lines within the sun’s corona that spread out into space, away from the sun. The result is a region where streams of atomic particles can follow the magnetic field and accelerate into space. These streams are collectively called the solar wind . (TOP OF THE PAGE)   (CLOSE WINDOW)

E

Extreme ultraviolet: Electromagmetic radiation, invisible to the naked eye, with wavelengths shorter than ultraviolet radiation and longer than X rays.  (TOP OF THE PAGE)   (CLOSE WINDOW)

F

Facula: Brighter-than-average regions on the sun’s surface that typically appear near a group of sunspots just before the sunspots themselves appear.   (TOP OF THE PAGE)   (CLOSE WINDOW)

Flare: A sudden outburst of energy from the sun that occurs near concentrated magnetic fields (known as active regions ) on the sun’s visible surface. Flares emit high-energy atomic particles and all forms of electromagnetic radiation into space.  (TOP OF THE PAGE)   (CLOSE WINDOW)

G

Gamma rays: High-energy electromagnetic radiation, invisible to the naked eye, with wavelengths shorter than X-rays. Gamma rays are emitted from the sun during large eruptions on the solar surface.  (TOP OF THE PAGE)   (CLOSE WINDOW)

Gauss: A unit of magnetic field strength.  (TOP OF THE PAGE)   (CLOSE WINDOW)

Geomagnetic field: The earth’s magnetic field. (TOP OF THE PAGE)   (CLOSE WINDOW)

Geomagnetic storm: A worldwide disturbance in the earth’s magnetic field.  (TOP OF THE PAGE)   (CLOSE WINDOW)

I

Infrared radiation: Electromagnetic radiation, invisible to the naked eye, with wavelengths longer than visible light and shorter than microwaves.  (TOP OF THE PAGE)   (CLOSE WINDOW)

Ionosphere: The part of the earth's atmosphere extending from 50 kilometers above the surface to about 1000 kilometers, and consisting of ionized gases. The aurora is produced when electrons from the sun's solar wind disturb the earth's magnetic field and interact with molecules in the ionosphere. (TOP OF THE PAGE)   (CLOSE WINDOW)

L

Limb: The edge of the sun or planet visible to an observer or instrument.   (TOP OF THE PAGE)   (CLOSE WINDOW)

M

Magnetic field: A map of the magnetic forces around any object (such as the sun or planet) that is magnetic. The map is created by measuring the influence of the field on a small magnetic compass.   (TOP OF THE PAGE)   (CLOSE WINDOW)

Magnetosphere: The region around an astronomical object (like a sun or planet) where the motion of charged atomic particles is influenced by the shape, strength, and direction of the object’s magnetic field .  (TOP OF THE PAGE)   (CLOSE WINDOW)

P

Penumbra: A dark region that surrounds an even darker central area of a sunspot.   (TOP OF THE PAGE)   (CLOSE WINDOW)

Plage: Bright regions of gases heated by concentrated magnetic fields in the solar chromosphere during the sun’s active periods. They appear near groups of sunspots just before the sunspots emerge.   (TOP OF THE PAGE)   (CLOSE WINDOW)

Prominence: Eruptions of clouds of solar material that extend into the outer chromosphere and inner corona . They can appear as loops (when they follow the sun’s magnetic field ) or as sprays (when ejected by the sun’s magnetic field ).  (TOP OF THE PAGE)   (CLOSE WINDOW)

S

Solar cycle: An 11-year cycle during which the number of sunspots varies predictably.   (TOP OF THE PAGE)   (CLOSE WINDOW)

Solar maximum: A period of increased solar activity when the number of sunspots reaches a maximum in the 11-year solar cycle.  (TOP OF THE PAGE)   (CLOSE WINDOW)

Solar minimum: A period of decreased solar activity when the number of sunspots reaches a minimum in the 11-year solar cycle. (TOP OF THE PAGE)   (CLOSE WINDOW)

Solar wind: The outward flow of charged particles from the sun into space.  (TOP OF THE PAGE)   (CLOSE WINDOW)

Sunspot: Cooler, darker area on the sun’s surface thought to be caused by concentrated, contorted magnetic fields that suppress convection of hot matter from the sun’s core.  (TOP OF THE PAGE)   (CLOSE WINDOW)

U

Ultraviolet radiation: Electromagmetic radiation, invisible to the naked eye, with wavelengths shorter than violet light and longer than X rays .   (TOP OF THE PAGE)   (CLOSE WINDOW)

Umbra: The dark central area of a sunspot .   (TOP OF THE PAGE)   (CLOSE WINDOW)

X

X rays: High-energy electromagnetic radiation, invisible to the naked eye, with wavelengths shorter than ultraviolet radiation and longer than gamma rays and cosmic rays.   (TOP OF THE PAGE)   (CLOSE WINDOW)

W

White light: Electromagnetic radiation composed of all wavelengths of light that is visible to the naked eye (red through violet).   (TOP OF THE PAGE)   (CLOSE WINDOW)