Copy of `Skyview NASA - Astrophysics Dictionary`

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Skyview NASA - Astrophysics Dictionary
Category: Sciences > Astophysics
Date & country: 11/09/2007, USA
Words: 223


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. 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 (SNR).

SXG
The Spectrum X-Gamma mission

synchronous rotation
Said of a satellite if the period of its rotation about its axis is the same as the period of its orbit around its primary. This implies that the satellite always keeps the same hemisphere facing its primary (e.g. the Moon). It also implies that one hemisphere (the leading hemisphere) always faces in the direction of the satellite's motion while the other (trailing) one always faces backward.

Thomson, William 1824-1907
also known as Lord Kelvin, the British physicist who developed the Kelvin scale of temperature and who supervised the laying of a trans-Atlantic cable. (11 k GIF)

time dilation
Stretching of time produced by relativity. Time dilation is a predicted effect of the cosmological paradigm.

ToFU
A suite of software tools developed at the OGIP to transform non-FITS information into FITS.

ultraviolet
Electromagnetic radiation at wavelengths shorter than the violet end of visible light; the atmosphere of the Earth effectively blocks the transmission of most ultraviolet light.

Van Allen, James A.
American physicist who discovered the Earth's radiation belts (that now bear his name) with an instrument aboard the first successful American satellite, Explorer 1.

Vela 5B
US Atomic Energy Commission (now the Department of Energy) satellite with an all-sky X-ray monitor

wave-particle duality
The principle of quantum mechanics which implies that light (and, indeed, all other subatomic particles) sometimes act like a wave, and sometimes act like a particle, depending on the experiment you are performing. For instance, low frequency electromagnetic radiation tends to act more like a wave than a particle; high frequency electromagnetic radiation tends to act more like a particle than a wave.

waveband
Portions of the electromagnetic spectrum. Examples of different wavebands include the infrared, visual, and radio wavebands.

wavelength
A property of a wave that gives the length between two peaks of the wave.

white dwarf
A star that has exhausted most or all of its nuclear fuel and has collapsed to a very small size. Typically, a white dwarf has a radius equal to about 0.01 times that of the Sun, but it has a mass roughly equal to the Sun's. This gives a white dwarf a density about 1 million times that of water!

Wien's displacement law
For a blackbody, the product of the wavelength corresponding to the maximum radiancy and the thermodynamic temperature is a constant. As a result, as the temperature rises, the maximum of the radiant energy shifts toward the shorter wavelength (higher frequency and energy) end of the spectrum.

WORM
Write-Once-Read-Many. A CD-ROM is a typical WORM medium: the CD-ROM is written once when it is etched and it cannot be written to again. However, it can be read any number of times.

WWW
The World Wide Web -- a loose linkage of Internet sites which provide data and other services from around the world.

X-ray
Electromagnetic radiation of very short wavelength and very high-energy; X-rays have shorter wavelengths than ultraviolet light but longer wavelengths than cosmic rays.

XANADU
X-ray analysis system maintained at the HEASARC

XIMAGE
Image analysis program in XANADU

XRONOS
Temporal analysis program in XANADU

XSELECT
A high-level tool to manage the FTOOLs

XSPEC
X-ray/gamma-ray spectral analysis package in XANADU

XTE
X-ray Timing Explorer, also known as the Rossi X-ray Timing Explorer (RXTE)