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Stellar parallax See parallax.Subatomic particle One of the
many kinds of particle that are
smaller than atoms. These include
electrons, neutrinos, and quarks.sunspot An area on the surface of
the sun that appears dark because
it is cooler than its surroundings.
sunspots are found in areas of
concentrated magnetic field.Supernova The result of the
collapse of a star, which causes an
explosion that may be many billions
of times brighter than the sun.Time dilation The phenomenon
whereby two objects moving
relative to each other, or in different
gravitational fields, experience
a different rate of flow of time.TNO Short for Trans-Neptunian
Object. Any minor planet (dwarf
planet, asteroid, or comet) that
orbits the sun at a greater average
distance than Neptune (30 AU).Transit The passage of a celestial
body across the face of a larger body.Wavelength The distance
between two successive peaks
or troughs in a wave.White dwarf A star with low
luminosity but high surface
temperature, compressed by
gravity to a diameter close to
that of Earth.Zodiac A band around the
celestial sphere, extending 9° on
either side of the ecliptic, through
which the sun, moon, and planets
appear to travel. The zodiac crosses
the constellations that correspond
to the “signs of the zodiac.”Redshift A shift in a spectrum
of light or other radiation toward
longer wavelengths that occurs
when the source of the light is
moving away from an observer.
Reflecting telescope A telescope
in which an image is formed by
reflecting light on a curved mirror.
Refracting telescope A telescope
that creates an image by bending
light through a converging lens.
Relativity Theories developed
by Albert Einstein to describe the
nature of space and time. See also
general theory of relativity.
Satellite A small body that
orbits a larger one.
Schwarzschild radius The
distance from the center of a
black hole to its event horizon.
SETI Short for Search for
Extra-Terrestrial Intelligence,
the scientific search for alien life.
Seyfert galaxy A spiral galaxy
with a bright, compact nucleus.
Sidereal Relating to the stars.
A sidereal day corresponds to
Earth’s rotation period measured
relative to the background stars.
Singularity A point of infinite
density at which the known laws of
physics appear to break down. It is
theorized that there is a singularity
at the center of a black hole.
Solar wind A stream of fast-
moving, charged particles
emanating from the sun that
flows out through the solar system.
It consists mostly of electrons
and protons.
Spacetime The four-dimensional
combination of the three
dimensions of space and one
of time. According to the theory
of relativity, space and time do
not exist as separate entities.
Rather, they are intimately
linked as one continuum.Spectrum The range of the
wavelengths of electromagnetic
radiation. The full spectrum
ranges from gamma rays, with
wavelengths shorter than an atom,
to radio waves, whose wavelength
may be many feet long.Spectroscopy The study of the
spectra of objects. The spectrum
of a star contains information about
many of its physical properties.Spiral galaxy A galaxy that
takes the shape of a central
bulge or bar surrounded by
a flattened disk of stars in a
pattern of spiral arms.Standard candle A celestial body
that has a known luminosity, such
as a Cepheid variable star. These
allow astronomers to measure
distances that are too large to
measure using stellar parallax.Star A luminous body of hot gas
that generates energy through
nuclear fusion.Steady State theory A theory
proposing that matter is constantly
created. The theory was an attempt
to explain the universe’s expansion
without the need for a “Big Bang.”Stellar aberration The apparent
motion of a star caused by movement
of an observer in a direction
perpendicular to the direction
to the star.GLOSSARY