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GALEX

Albert Einstein
the German-American physicist who developed the Special and General Theories of Relativity, which along with quantum mechanics is the foundation of modern physics. Awarded the Nobel prize for physics in 1921.
Astronomy
the scientific study of matter in outer space, especially the positions, dimensions, distribution, motion, composition, energy, and evolution of celestial bodies and phenomena.
Atom
the smallest particles of an element that can exist either alone or in combination, considered a source of vast potential energy.
Attitude
the orientation of the GALEX with respect to the Earth and the Sun. For science observations the telescope is pointed toward a science target in the sky. During the day side of the orbit the attitude of the satellite is adjusted so that the solar panels can collect sunlight and recharge the on-board batteries.
Background Radiation
the background of radiation from the Universe is strongest in the frequency range 3 x 108 to 3 x 1011 Hertz and was first discovered to be coming from all directions in the sky in 1965. It is believed to be the cosmologically redshifted radiation released by the Big Bang itself.
Big Bang
a theory of cosmology in which the expansion of the universe is presumed to have begun with a primeval explosion.
Black Hole
a region in space where gravity is so strong that not even light can escape from it. Black holes in our galaxy are thought to be formed when stars more than ten times as massive as our Sun end their lives in a supernova explosion. There is also evidence indicating that supermassive black holes (more massive than ten billion Suns) exist in the centers of some galaxies.
Blueshift
an apparent shift toward shorter wavelengths of spectral lines in the radiation emitted by an object caused by motion between the object and the observer which decreases the distance between them. See also Doppler effect.
Cosmic
of or relating to the cosmos, the extraterrestrial vastness, or the Universe in contrast to the Earth alone.
Cosmology
the astrophysical study of the history, structure, and dynamics of the Universe.
Density
the ratio between the mass of an object and its volume. In the metric system, density is measured in grams per cubic centimeter (or kilograms per liter). For example the density of water is 1.0 grams per cubic centimeter; iron is 7.9 grams per cubic centimeter; lead is 11.3 grams per cubic centimeter.
Doppler Effect
the apparent change in wavelength of sound or light caused by the motion of the source, observer or both. Waves emitted by a moving object as received by an observer will be blueshifted (compressed) if approaching, redshifted (elongated) if receding. It occurs both in sound and light. How much the frequency changes depends on how fast the object is moving toward or away from the receiver.
Electromagnetic Spectrum
the full range of frequencies, from radio waves to gamma rays, that characterizes light. There is a relation ship between the amount of energy electromagnetic radiation carries and the frequency. Radio waves are low frequency and low energy radiation while gamma rays at the other end of the spectrum are high frequency and high energy radiation. Visible light, that which our eyes can see, is also part of the electromagnetic spectrum.
Electron
a fundamental particle of very low mass, carrying a negative electric charge and found in all atoms. Electrons can be energized or even torn from atoms by light and by collisions, and they are responsible for many electric phenomena in solid matter and in plasmas.
Energy
loosely, anything that can cause a machine to move. For example, energy is contained in moving water, water raised to a high place, heat, or magnetic fields. The energy of fast ions and electrons (measured in "electron volts") is a measure of their speed, and it enables them (for instance) to penetrate matter.
Frequency
the number of back-and-forth cycles per second, in a wave or wave-like process. Expressed this way, the frequency is said to be given in units of Hertz (Hz), named after the scientist who first produced and observed radio waves in the lab. Alternating current in homes in the US goes through 60 cycles each second, hence its frequency is 60 Hertz; in Europe it is 50 cycles and 50 Hertz. Radio signals have a frequency in the thousand (kilo) Hertz range and because all electromagnetic radiation can be described as a wave, visible light also has a frequency.
Galaxy
a component of our Universe made up of gas and a large number (usually more than a million) of stars held together by gravity.
Gamma Ray
the highest energy, shortest wavelength electromagnetic radiation. Usually, they are thought of as any photons having energies greater than about 100 kilo electronvolt.
General Theory of Relativity
the geometric theory of gravitation developed by Albert Einstein, incorporating and extending the theory of special relativity to accelerated frames of reference and introducing the principle that gravitational and inertial forces are equivalent. The theory has consequences for the bending of light by massive objects, the nature of black holes, and the fabric of space and time.
Gigabyte
a collection of a billion bytes of information, usually in a computer or on a computer storage device. A byte contains a string of eight binary digits (bits) each with a value of either 0 or 1. A byte is the basic unit of computer information.
Gravity
one of the fundamental physical forces of nature attracting two bodies to each other.
Grism
the combination of a prism with grooves cut into one surface that allows light to be dispersed into a spectrum. The use of the grooves (called a grating) causes the spectrum to emerge from the prism at an exact angle. Without the grating the light must be passed through a small slit for the spectrum to be measured. The GALEX grism will allow the spectra of many hundreds of stars and galaxies to be measured from a single image of the sky.
Helium
the second lightest and second most abundant element in the Universe. The helium atom consists of a nucleus of two protons and two neutrons surrounded by two electrons. Helium was first discovered in our Sun. Roughly 5 percent of our Sun is helium.
Hydrogen
the lightest and most abundant element in the Universe. A hydrogen atom consists of one proton and one electron. Hydrogen composes nearly 95 percent of the Sun, but only tiny amounts are found on the Earth.
Hubble Space Telescope (HST)
NASA's space telescope, which orbits 500 kilometers (310 miles) above Earth to observe the Universe. HST has taken more than 330,000 separate observations of the Universe, observed more than 25,000 astronomical targets, and to date has created a data archive of over 7.3 terabytes. HST is the first scientific mission of any kind that is specifically designed for routine servicing by spacewalking astronauts.
Infrared
electromagnetic radiation at wavelengths longer than the red end of visible light and shorter than microwaves (roughly between 1 and 100 microns). Almost none of the infrared portion of the electromagnetic spectrum can reach the surface of the Earth, although some portions can be observed by high-altitude aircraft (such as the Kuiper Observatory) or telescopes on high mountaintops (such as the peak of Mauna Kea in Hawaii).
Ions
an atom with one or more electrons stripped off, giving it a net positive charge.
Lemaitre
the Belgian priest and mathematician who first proposed the theory of the Big Bang, the origin of the Universe.
Light
the common term for electromagnetic radiation, usually referring to that portion visible to the human eye. However, other bands of the electromagnetic spectrum are also often referred to as different forms of light.
Local Group
the group of 30 galaxies closest to (and including) our own Milky Way, that are clustered together. The local group is also part of a larger cluster of about one hundred galaxies called the Virgo cluster.
Luminosity
the rate at which a star or other object emits energy, usually in the form of electromagnetic radiation.
Matter
containing mass, a measure of the total amount of material in a body, defined either by the inertial properties of the body or by its gravitational influence on other bodies.
Microwave
electromagnetic radiation which has a longer wavelength (between 1 millimeter and 30 centimeter) than visible light. Microwaves can be used to study the Universe, communicate with satellites in Earth orbit, and cook popcorn.
Milky Way
the spiral shaped galaxy in which we live, made up of ten billion stars including our Sun. We see the Milky Way as a bright band of stars across the sky because our Sun lies in one of the spiral arms.
Nebula
a diffuse mass of interstellar dust and gas. A reflection nebula shines by light reflected from nearby stars. An emission nebula shines by emitting light as electrons recombine with protons to form hydrogen. The electrons were made free by the ultraviolet light of a nearby star shining on a cloud of hydrogen gas. A planetary nebula results from the explosion of a solar-like type star.
Neutrino
a fundamental particle produced in massive numbers by the nuclear reactions in stars; they are very hard to detect because the vast majority of them pass completely through the Earth without interacting.
Neutron
a fundamental particle with approximately the mass of a proton, but zero charge, commonly found in the nucleus of atoms.
Nuclei
plural for nucleus, the positively charged central portion of an atom that comprises nearly all of the atomic mass.
Next Generation Space Telescope
NASA's next space-based observatory now in the planning stages. It is also called the James Webb Space Telescope. It will carry instruments that are sensitive to infrared light.
Orbit
the path of an object that is moving around a second object or point.
Orientation
a satellite can spin on 3 axes, up-down, left-right, and clockwise-anticlockwise (called pitch, yaw and roll). The position of the satellite with respect to the Earth and the Sun and the direction in which the GALEX telescope is pointing determines the orientation of the satellite.
Ozone
a molecule containing three atoms of oxygen. It is a beneficial component of the upper atmosphere that protects the Earth from harmful ultraviolet radiation from the Sun.
Photon
a unit of electromagnetic energy (light). Photons have no electric charge and are generally regarded as particles with zero mass.
Primeval
existing in or persisting from the beginning (as of a Solar System or Universe).
Primordial
first created or developed.
Prism
transparent solid body, often having triangular bases, used for dispersing light into a spectrum or for reflecting rays of light.
Proton
a fundamental particle with a positive charge commonly found in the nucleus of atoms.
Quasar
an enormously bright object at the edge of our Universe that emits massive amounts of energy. In an optical telescope, they appear point-like, similar to stars, from which they derive their name. Their high luminosity is created from matter falling into a supermassive black hole in the centers of distant galaxies.
Radiation
some type of electromagnetic wave: radio, microwave, light (infrared, visible or ultraviolet), x-rays or gamma rays are all types of radiation.
Radio Waves
are low energy electromagnetic radiation, like light waves and gamma rays. These waves pass through empty space and are often used on Earth to communicate over large distances. Radio waves are also detected from objects in space like stars, galaxies and quasars.
Redshift
a shift toward longer wavelengths of the radiation caused by the emitting object moving away from the observer. When this occurs we see the light from the object become more red. See also Doppler effect.
Solar System
the region within which the Sun, and all the planets and other bodies that travel around it, move.
Space
the expanse in which the Solar System, stars, and galaxies exist.
Spectral Lines
when astronomers look at the spectrum of light from a star or galaxy they see that some narrow bands of color are brighter than others. These are spectral lines. The precise wavelength of these lines tells scientists what type of atom emitted the light.
Spectrometer
the instrument connected to a telescope that separates the light signals into different wavelengths, producing a spectrum.
Spectroscopy
the production and investigation of spectra.
Spectrum
a continuum of color formed when a beam of white light is dispersed (as by passage through a prism) so that its component wavelengths are arranged in order. All forms of electromagnetic radiation can be dispersed to form a spectrum.
Speed of Light
the speed at which electromagnetic radiation propagates in a vacuum; it is defined as 299 792 458 m/s (186,000 miles/second). Einstein's Theory of Relativity implies that nothing can go faster than the speed of light.
Star
a large ball of gas held together by gravity that creates and emits its own radiation from a nuclear fusion process.
Stellar
star-like.
Supernova
the death explosion of a massive star, resulting in a sharp increase in brightness followed by a gradual fading. At peak light output, supernova explosions can outshine a galaxy containing a billion stars. The outer layers of the exploding star are blasted out in a radioactive cloud. This expanding cloud, visible long after the initial explosion fades from view, forms a supernova remnant.
Star Formation Rate
stars take millions of years to form out of clouds of gas and dust within galaxies. However there may be many stars forming at the same time in different parts of a galaxy. Our Milky Way galaxy is forming stars at a rate of about one every year but some galaxies are observed to be forming stars much faster. This star formation rate may be as high as many hundreds of new stars every year.
Terabyte
a collection of a thousand billion bytes (1,000,000,000,000 = 1012) of information, usually in a computer or on a computer storage device. See gigabyte. By the end of its mission the GALEX archive will contain over 30 terabytes of information about the Universe.
Ultraviolet (UV)
electromagnetic radiation of shorter wavelength than visible light. UV cannot be seen by the eye, and much of it is absorbed by ozone, a molecule of oxygen, at altitudes of 30-40 km above the Earth. Satellite telescopes, however, can and do view stars, galaxies, and the Sun in UV.
Universe
the whole body of things and phenomena observed that exists.
Visible Light
electromagnetic radiation at wavelengths which the human eye can see. We perceive this radiation as colors ranging from red (longer wavelengths; ~ 700 nanometers) to violet (shorter wavelengths; ~400 nanometers).
Wavelength
the distance between adjacent peaks in a series of periodic waves. Also see electromagnetic spectrum.
White Dwarf
a small, hot, faint star, essentially the leftover and exposed core of a red giant star that has puffed off its outer layers to form a planetary nebula. It is the last stage of evolution for stars like our Sun.
X-Rays
electromagnetic waves of short wavelength, capable of penetrating some thickness of matter. Medical x-rays are produced by letting a stream of fast electrons come to a sudden stop at a metal plate; it is believed that x-rays emitted by the Sun and stars also come from fast electrons. 

 

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