Descriptionary

spacetime the four-dimensional continuum com­posed of the three dimensions of space with time, through which an event can be precisely plotted.

spectroscope an instrument astronomers use to sep­arate light into its component colors, creating a spec­trum that can be analyzed to determine what elements a celestial body is made of.

spiral galaxy a galaxy in the configuration of a spiral or pinwheel, with the oldest stars clustered in a sphere in the center and the youngest stars forming the outer arms.

star a fiery sphere of gas; a sun.

starburst galaxy a galaxy in which new stars are rapidly forming.

superior planets the planets Mars, Jupiter, Saturn, Uranus, Neptune, and Pluto, whose orbits are farther from the Sun than the Earth's.

supermassive black hole a black hole that resides at the center of a galaxy and may contain the mass of millions of consumed stars.

sunspot cooler area visible as a dark spot in the surface of the Sun.

supernova an exploding star that increases its brightness thousands of times, dimming only after a period of months.

supernova remnant a nebula surrounding the site of an earlier supernova explosion.

symbiotic stars two stars so close together they exchange gases and mass.

terminator the line that delineates the dark side of a planet or moon from the lighted side.

transit method a method of discovering new plan­ets by observing if a star dims temporarily, which sometimes means a planet or another star has passed in front of it.

uranography the mapping of the stars.

uranometry the scientific measurement of the dis­tances, brightness, and positions of celestial bodies.

variable star a star with a varying magnitude or brightness.

white dwarf a tiny star comparable in volume to the Earth but with a mass equal to the Sun's and a density a million times that of water.

young referring to a moon or planetary surface that has a small number of craters, an indication of the planet's age.

zenith the point in the sky directly overhead.

zodiac the 12 constellations aligned along the eclip­tic through which the Sun, Moon, and most of the planets travel.

zodiacal light a hazy band of light consisting of dust illuminated by the Sun and sometimes seen from Earth.

sun

acronical occurring at sunset

bright spots X-ray and ultraviolet flashes on the Sun's surface closely associated with intense magnetic fields.

chromosphere the reddish solar atmosphere between the photosphere and the corona.

corona the tenuous outer atmosphere of the Sun extending into space for millions of miles but gener­ally only visible during an eclipse.

coronal holes holes in the Sun's Corona created by openings in the Sun's magnetic fields through which are emitted high-speed solar wind particles; largely responsible for the magnetic storms on Earth.

coronal mass ejection a massive bubble of gas that periodically explodes from the Sun and discharges a wave of charged particles into space and toward Earth, disrupting satellite functioning and occasionally black­ing out entire cities. Also known as a solar storm.

facula a bright spot on the surface of the Sun, espe­cially near its perimeter.

filament a finger of cool gas suspended above the photosphere that may appear slightly darker against the brilliance of the Sun's surface.

flare an eruption on the Sun, causing a brightening and a jet of radiation and particles to be ejected into space, sometimes toward Earth. Flares occur most often near sunspots.

gegenschein a faint reflection of the Sun that may form on dust particles and appears in the evening sky opposite where the Sun has set.

granulation a reticular pattern of small bright areas or cells on the surface of the Sun.

helio referring to the Sun.

heliocentric relating to the Sun as a center; relative to the Sun.

heliolatry worship of the Sun.

Helios in Greek mythology, the sun god who drove his chariot across the sky from east to west each day.

heliosphere an area encompassing the area of the Sun and solar system out beyond Pluto, where the solar magnetic field can be found.

heliotaxis the movement of an organism in response to sunlight.

heliotherapy sunlight therapy.

heliotrope any plant that bends or turns to follow the daily path of the Sun.

mock sun a false image of the Sun, often watery in appearance, formed by the refraction or bending of light by hexagonal crystals of ice in the air. Also known as a sun dog.

neutrino produced by thermonuclear fusion in the Sun's core, a massless particle that has the bizarre abil­ity to pass through physical objects such as the Earth.

penumbra the outer, lighter-colored border of a sunspot.