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Aberration-corrected toroidal grating -A kind of
diffraction grating (see Diffraction Grating)
Absorption cell - A cell that is filled with a particular
gas that absorbs light of particular wavelengths.
Angstrom - A unit of measurement, equaling 10 -10
meter or 10 -8 centimeters, usually used to express short wavelengths.
Aperture -An adjustable opening in an instrument
(like a camera) that controls the amount of light that can enter.
ASI - The Italian Space Agency
Attitude control - The act of controlling the position
of a spacecraft relative to the direction in which it's moving.
Baffle - A device that regulates the flow of light
so that it all comes from a particular direction.
Channel - A specific frequency band for transmitting
or receiving signals, (i.e. different signal frequencies give you different
television channels). For UVIS, a part of the instrument sensitive
to a particular frequency band.
Channel electron multiplier (CEM) - A light-sensitive
device that amplifies dim signals.
CODACON (Coded Anode Converter) - A devise, at the
output of the detector, that converts the data from the spectrometer
into an image format.
Command and Data Subsystem (CDS) - Cassini's main
computer that commands and collects data from the various instruments
and packages it to be sent back to NASA?
Concave grating spectrometer - A spectrometer whose
diffraction grating has a concave shape.
Detector - A light-sensitive device that produces
electrical signals when illuminated.
Diffraction Grating - A grooved optical element
that has been deformed to reflect light of many colors. It acts like
a prism to produce a spectrum.
Electromagnetic Spectrum - See "Spectra".
Also see graphic
ESA - European Space Agency
Filament current controllers - Controls the amount
of current sent to the HDAC filaments, and thus, their temperature.
Focal plane - The location where the rays from a
distant object merge: This is where we place the detector.
FPSCAN - A Cassini observation where the spacecraft
turns slowly to fields and particles all around it.
Grating ruling density - The number of grooves per
mm on the diffraction grating.
GSE (UVIS Ground Support Equipment) - Equipment
used for testing and operating UVIS before launch.
Imaging microchannel plate detector - A light detector
formed from glass full of many small channels that creates an image
of the light shining on it.
Imaging, pulse-counting detector - Each bit
of light that falls on the detector creates a pulse of electricity.
See "imaging microchannel plate detector".
Imaging spectroscopy - Imaging spectroscopy
is what UVIS does--it takes spectrographic measurements and turns them
into a graph, but it can also turn the points on the graph into digital
data that can then be made into pictures (images). Because humans can't
see UV wavelengths of light, we assign different "false colors" to
the different wavelengths that allows us to produce a picture out of
the data that our eyes can appreciate.
Ion pump - A small vacuum pump that works by ionizing
JPL - NASA's Jet Propulsion Laboratory in Pasadena.
LASP - Laboratory for Atmospheric Research in Boulder,
Colorado - A research facility of the University of Colorado and the
builders of the UVIS instrument.
Logic - Computer circuitry
Lyman-alpha emission - Light emitted by hydrogen
atoms at a wavelength of 1216Å.
Magnetosphere - A magnetic environment surrounding
an object, like a planet, in a fashion similar to an atmosphere.
MDT - Mountain Daylight Time -- The time in Boulder,
Colorado, where LASP is. (Except in winter when it's MST -- Mountain
MgF 2 windows - Windows made from crystals of magnesium
Microchannel plate detector - (see above under "Imaging...")
Nanometer - A unit of measurement that is one billionth
(10 -9 ) of a meter.
NASA - National Aeronautics and Space Administration,
headquartered in Washington, DC with field centers across the country.
Neutrals - Particles, objects or systems that have
no electrical charge.
Objective lens - A lens that focuses light on the
Optical coatings - Coatings specifically made for
the lenses of light-sensitive devices.
Orbiter - A spacecraft whose purpose is to orbit
around an object like a planet or a satellite (moon).
Payload - The instruments, crew or equipment carried
by a spacecraft.
Photochemistry - The chemistry of the effects of
light on chemical systems.
Photometer - An instrument for measuring the intensity
Photomultiplier tube detector - A vacuum tube that
amplifies and detects weak light signals.
Photons - Packets of radiant energy: quanta
Pulse- amplifier-discriminator - The part of UVIS
that counts responses (pulses) to light falling on the detector. It
discriminates between light and background noise.
Reflecting telescope - A telescope where mirrors
are the optical elements, not lenses.
Remote sensing - Gathering information from far
away; like the UVIS instrument will gather data on ultraviolet light
in the saturnian system and send it back to Earth.
Remote Sensing Palette (on Orbiter) - The area on
Cassini to which experiments (like the UVIS instrument) are secured
Resonance absorption cells - Cells filled with gas
that absorbs at its atoms' resonant frequencies (same as "absorption
Satellite - A body that revolves around another
body like a Saturn's moon Titan revolving around Saturn; or a man-made
object revolving around a body, like Explorer 1 orbiting Earth. We
call the moons of planets satellites instead of moons so as not to
confuse them with the Earth's Moon.
Signal-to-noise-ratio (SNR) - A ratio to measures
the clarity of a data source or transmission, usually a ratio of the
signal amplitude and the noise amplitude. The higher the SNR, the less
the interference with reception.
Slew - To turn something on an axis or to turn sharply
or veer. Cassini slews to point its cameras at targets of interest.
Slit changer (entrance slit) - There are three slits
each on UVIS EUV and FUV telescopes and that allow light into the instrument
to be measured. The slit changer switches between them to measure with
different spectral resolutions.
Solar blind CsI photocathode - The active element
that is insensitive to reflected sunlight only seeing light with shorter
Solar flux - The amount of light from the Sun.
Solar or stellar occultation - Watching the Sun
(or a star) pass behind an object of interest, like a planet or Saturn's
rings. Observing solar occultations help us discover things like the
vertical structure of clouds, gases in atmospheres and active processes
that move the particles in Saturn's rings.
SOPC (UVIS Science Operations and Planning Computer) - The
computer we use to plan observations and send them to JPL.
Spectra, Spectrum - Spectra is the plural of spectrum,
which is a series of energies (like light) arranged according to wavelength,
or frequency. The electromagnetic
spectrum is an array of radiation
that is divided into a number of sub-portions, where the boundaries
are only vaguely defined. They extend from the shortest cosmic rays,
through gamma rays, X-rays, ultraviolet light, visible light, infrared
radiation, microwave and all other wavelengths of radio energy.
Spectral resolution - The ability to distinguish
two spectral features close to one another; the smallest difference
in wavelength between two such distinguished features.
Spectrograph - A spectroscope that measures wavelengths
of light (spectra) and then displays the data as a graph. UVIS is an imaging spectrograph,
which means it can also display the points of the graph as a picture
(see Imaging Sepctrosopy).
Spectroscope - A machine (instrument) for producing
and observing spectra.
Spectroscopic measurements - The measurements taken
by a spectrograph.
Spectrometer - A spectroscope equipped with the
ability to measure wavelengths.
Telemetry Data Server (TDS) - Telemetry data are
the spacecraft observations. They are stored temporarily on the TDS.
Ultraviolet (UV)- (Extreme Ultraviolet and Far Ultraviolet)
Ultraviolet light (UV) is a portion of the complete electromagnetic
spectrum Ultraviolet is a portion of the spectrum that is a shorter
wavelength than visible light; roughly, with a wavelength interval
from 100 to 4000 angstroms. Ultraviolet radiation from the Sun is responsible
for many complex photochemical reactions like the formation of the
ozone layer. Extreme and far ultraviolet wavelengths are different
portions of the ultraviolet portion of the spectrum, with extreme being
between 55.8-118 nanometers and far being between 110-190 nanometers.
Undispersed (zero-order) light - A specular reflection
off the diffraction grating which acts like a mirror.
Uplink Product Generation System (UPGS) - A process
consisting of manpower, software and hardware that generates the sequencing
of the UVIS instrument according to the plan of the science team.
UTC - Coordinated Universal Time, also known as
Greenwich Mean Time (GMT), Greenwich Mean Time is based upon the time
at the zero degree meridian that crossed through Greenwich, England
and is used as a world time and date standard.
Weight-relieved (aluminum cases) - UVIS is
built out of aluminum that has been carved out to the dimensions necessary
in order to be as light as possible.