Astronmy Glossary
N-Z
NASA
The National Aeronautics and Space Administration, a federal agency established
in 1958 to administer all non-military aeronautical research and space
programs in the United States.
Navigation satellites
Satellites that help aircrafts
and ships to identify their exact locations.
Nebula
A region of gas and dust in a galaxy. They
appear to be fuzzy.
Neutron star
A very small, dense star that is so tightly
packed together that the protons and electrons have been compressed to
form neutrons.
Nova
A faint star that suddenly becomes bright, becoming
visible from where no star had been seen before. Only two or three novae
are discovered each year. Most novae are binary stars.
Nuclear fission
The process in which the nucleus of a heavy atom splits into two or more
parts, releasing energy and two or three free neutrons.
Nuclear fusion
The process in which light nuclei fuse together to make one heavier nucleus,
releasing energy as they do so.
Open cluster
A shapeless, loosely packed cluster of stars.
Orbit
The path that an astronomical body follows as
it moves around another astronomical body.
Phase
The portion of any bright body that is visible to the observer.
Photometer
A device that is used to measure the brightness
of an object.
Photometry
The measurement of an object's brightness.
Photon
A particle of light.
Photosphere
The visible surface of the Sun.
Planet
A body that shines by reflecting sunlight. Planets can be made out of
rock and metal, like Earth, or out of gas, like Jupiter.
Planetary nebula
A gaseous shell surrounding a hot
central star. They often look like planets, but they are much hotter:
the surface temperature is anywhere from 30,000 to 150,000 degrees Celsius.
Plasma A hot gas that consists of negatively charged electrons and positively charged atomic nuclei, or ions. The atoms of gas are broken into these parts by collisions between the atoms, or as a result of being struck by high-energy ultraviolet radiation from a nearby star.
Polar distance
The angle between an object and the
celestial pole.
Proper motion
The motion of a star across the sky.
It is expressed in arc seconds per year.
Protoplanet
A cloud of gas, rocks, and dust particles
that are in the process of forming into a planet.
Protostar
The early stage in a star's formation before the onset of
nuclear burning at the core of the star.
Pulsar
A radio source that emits short pulses of radiation
at regular intervals.
Quantum Theory
The set of physical laws that apply primarily on a very small scale, the
size of atoms or smaller.
Quasar
An object which appears as a star-like point
of light, but emits more energy than an entire galaxy. Many quasars also
emit radio waves.
Radar astronomy
The study of the bodies in the solar system by radio waves reflecting
off of them. A radio telescope is used to transmit a powerful pulse of
radio waves, and then to detect the faint echo that returns a few seconds
later.
Radio astronomy
The study of the universe at radio
wavelengths.
Radio galaxies
Distant galaxies that are sources of
powerful radio waves. Their radio output is up to a million times that
of our own galaxy.
Radio telescopes
Instruments for receiving radio waves
from space. A radio telescope consists of an antenna, an amplifying system,
and a recorder to preserve the observations.
Red dwarf
A star that has a low surface temperature,
2,000 to 3,000 degrees Celsius, and a diameter about half that of the
Sun.
Red giant
A star that has a low surface temperature,
2,000 to 3,000 degrees Celsius, and a diameter between 10 and 100 times
that of the Sun.
Redshift
The amount that wavelengths of light and
radiation from distant galaxies and quasars are increased because of the
expansion of the Universe.
Reflecting telescope
A telescope that has a concave
mirror which collects and focuses the light from a celestial object. The
majority of modern telescopes are reflectors because they are inexpensive
and compact.
Refracting telescope
A telescope that has a large
lens that collects and focuses the light from the object being observed.
Relativity
A theory to the structure of space and
time, and its relation to gravity and motion. This theory was first introduced
by Albert Einstein in 1905.
Resolution
The ability of a telescope to identify
fine details.
Satellite
Any small object orbiting a larger body.
Schmidt telescope
A wide-angle photographic telescope
that was first constructed by Bernhard Voldemar Schmidt in 1930. This
telescope uses a spherical mirror with a correcting lens in front which
increases the field of view to make it larger than normal reflecting telescopes.
Scintillation
The "twinkling" of a celestial object
or the rapid variations in a star's brightness. This twinkling is caused
by changes of the air temperature in the Earth's atmosphere. Changes in
air temperature causes turbulence which varies the bending of the light
entering the atmosphere.
Siderite
An iron meteorite.
Siderolite
A stony-iron meteorite which contains nickel,
iron and stony minerals.
Solar system
The group of planets, comets, and asteroids
that orbit the Sun and give a gravitational pull that dominates space
in all directions.
Solar wind
A continuous stream of protons and electrons
which is emitted by the Sun in all directions.
Space probe
Any instrument-carrying
device sent from Earth to study another celestial body, or to take measurements
of the conditions in space.
Space station
A large orbiting spacecraft made for
long-term human habitation in space.
Special Theory of Relativity
A description of the relationships and interactions between moving objects.
The 'special' theory only applies to the special case of objects moving
at constant speeds in straight lines. It does not deal with accelerated
motions.
Speckle interferometry
A technique that is used to
reconstruct star images that have been distorted by atmospheric turbulence.
Spectroscope
A device used to observe the spectrum.
Spectroscopy
The study of the spectra of heavenly bodies.
Spectrum
The entire range of electromagnetic radiation, from gamma rays to radio waves.
Spiral galaxy
A type of galaxy in which many of the stars and nebulae lie in spiral arms.
Star
A bright ball of gas, such as the Sun.
Star cluster
A collection of stars that are held together by their own gravity.
Steady State hypothesis
The idea that the universe has the same appearance to observers wherever they are in it.
Sun
The star that is the central body of our solar system.
Sunspot
A relatively cool, dark area on the surface of the Sun.
Supergiant stars
The brightest, largest stars that
are formed when stars heavier than the Sun move into old age. They burn
out very quickly so they are rarely seen.
Supernova
A star that explodes and loses most of its
mass.
Telescope
A device that collects and magnifies light.
Titan
The largest satellite of Saturn, and the only
moon in our solar system that has a substantial atmosphere.
Transit
The moment when a celestial body crosses the
meridian, the north-south line in the sky.
UFO
Unidentified Flying Object.
Ultraviolet astronomy
The study of the universe in the ultraviolet part of the electromagnetic
spectrum, which is located between visible light and X-rays.
Uncertainty Principle
A feature of the quantum theory which says that for any object certain
pairs of properties, such as position and momentum, are linked so that
they cannot both be precisely determined at the same time.
Variable stars
Stars whose light reaching the Earth varies in brightness.
Very Long Baseline Interferometry (VLBI)
A technique of linking distant radio telescopes together to form an interferometer.
Wavelength
The term that is used to describe a wave's motion.
White dwarf
A star which has about the same mass as the Sun, but occupies a volume about the same as the Earth.
X-ray astronomy
The study of the universe at X-ray wavelengths.