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AACS: Attitude and Articulation Control

AAS: American Astronomical Society

AAT: Anglo-Austrailian Telescope

AGB: Asymptotic Giant Branch

AGN: Active Galactic Nuclei

AGU: American Geophysical Union

Albedo: Reflectivity; the ratio of reflected light to incident light. The fraction of sunlight that a body reflects.

ALOT: Adaptive Large Optics Technologies

AMSD: Advanced Mirror System Demonstrator

AO: Announcement of Opportunity

Aperture: The diameter of an opening; the diameter of the primary lens or mirror of a telescope.

Apex: The point towards which a body is moving.

Aphelion: The point in orbit where a body is farthest from the Sun.

Apogee: The point in orbit where a body is farthest from Earth.

ARC: Ames Research Center

Arc minute: 1/60 of a degree.

Arc second: 1/3600 of a degree.

ASI: Italian Space Agency

ASIC: Application Specific Integrated Circuit

ASPEN: Autonomous Scheduling and Planning Environment

Asteroid Belt: A 1/2-AU-wide region between the orbits of Mars and Jupiter where the most asteroids are found.

Astronomical Unit (AU): Unit of distance, equal to the distance of the Earth from the Sun, about 150 million kilometers (93 million miles).

Astrophysics: That part of the astronomy dealing with the physics of astronomical objects and phenomena.

ASWG: Ad hoc Science Working Group

ATIS: Automated Telescope Instruction Set

AU: Astronomical Unit (Earth orbital radius)

AURA: Association of Universities for Research in Astronomy

Azimuth: Motion around a vertical axis; for instance, a measure of position around the horizon.

Backscattering: Reflecting light back in the direction of the source.

Bandpass: Wavelength range over which an observation is made. This is measured in microns (one millionth of a meter) for the JWST. The JWST will have near-infrared (NIR) bandpasses covering the wavelength range 1-5 microns and possibly thermal-infrared (TIR) bandpasses as well, covering the range 5-30 microns.

Beryllium: A lightweight metallic element (symbol: Be, atomic number 4), present in emerald and beryl stones. The JWST primary mirror will be made of beryllium.

Big Bang: The common term for the start of the universal expansion---when all matter was clustered at the 'beginning' and it 'exploded.' This expansion continues to the present day---galaxies are still moving apart from one another, as measured by redshift.

Black Hole: An object whose gravity is so strong that the escape velocity of light exceeds the speed of light.

BLIP: Background Limited Performance

BLR: Broad Line Region

Brown Dwarf: An object that is bigger than a planet but is too small to ignite internal nuclear fusion.

C&TS: Command & Telemetry (Processing) System

Calibration: The process of adjusting an instrument so that its reading can be correlated to the actual value being measured.

CCD: Charge Coupled Device

CCS: Control Center System (HST)

CDS: Correlated Double Sampling

CFHT: Canadian-French-Hawiian Telescope

CGRO: Compton Gamma Ray Observatory

Charon: The only known satellite of Pluto.

CMB: Cosmic Microwave Background

CNES: Centre National d'Etudes Spatiales

COBE: Cosmic Background Explorer

Comet: A small body of ice and dust in orbit around the Sun. While passing near the sun, a comet's vaporized ice become its "tail"

Constellation: A group of stars that, from the vantage point of Earth, appear to make a shape. They are often named after mythological characters, people, animals, and things.

Convection: A transfer of heat energy by circulation through a gas or liquid.

Corona: The Sun's outer atmosphere.

Coronagraph: An instrument used to block out the bright light from the sun or other stars so that nearby faint objects are visible.

Cosmology: The study of the origin, evolution and structure of the universe (the cosmos).

COSPAR: Committee on Space Research

COSTAR: Corrective Optics Space Telescope Axial Replacement (HST)

COTS: Commercial Off-The-Shelf

CPI: Continuous Process Improvement

Crater: A round impression left in a planet or satellite from a meteoroid collision.

Cryogenic: Relating to extremely low temperatures.

CSA: Canadian Space Agency

CSC: Computer Sciences Corporation

DARA: Deutsche Agentur fur Raumfahrt-angelegenheiten

Dark matter: A form of matter which has not been directly observed but whose existence has been deduced by its gravitational effects.

DCATT: Developmental Cryogenic Active Telescope Testbed

Density Wave: A kind of wave, similar to sound waves, induced in a flat plane of a resisting medium (such as the rings of Saturn) by gravitational forces, often assuming the form of a tightly wound spiral.

Design Reference Mission: The sample science program that is being used to help define engineering parameters for the JWST. The DRM is made up of astronomical targets, their brightnesses, space density, observing wavelength and resolution.

DFS: Dispersed-Fringe Sensor

DM: Deformable Mirror

DOF: Degree(s) of Freedom

Downlink: A radio connection wherein a spacecraft can communicate to Earth.

DPU: Data Processing Unit

DQE: Detective Quantum Efficiency

DRM: Design Reference Mission

DS-1: Deep Space-1 mission

DS-4: Deep Space-4 mission

DSN: Deep Space Network (JPL)

DSP: Digital Signal Processor

Eccentric: Noncircular; elliptical (applied to an orbit).

ECF: European Coordinating Facility

Eclipse: When one celestial object moves into the shadow of another.

EFOSC: ESO Faint Object Spectrograph & Camera

EGS: European Geophysical Society

Elevation: Angular distance above the horizon.

ESA: European Space Agency

ESO: European Southern Observatory

ESOC: European Space Operations Centre, Darmstadt (Germany)

ESRIN: ESA's Documentation and Information Centre (Italy)

ESTEC: European Space Research and Technology Centre, Noordwijk (The Netherlands)

EUV: Extreme Ultra-Violet

EXOSAT: European X-ray Observatory Satellite

Extrasolar Planet: Planets that orbit stars other than our own Sun.

Fault protection: A program built into a spacecraft which detects errors and faults in the spacecraft before they become monstrous and fixes them or reroutes to avoid them.

FD&C: Fault Detection and Correction

FES: Fine Error Sensor

FGS: The JWST Fine Guidance Sensor instrument. FGS will primarily help to keep JWST pointed onto its target, but will also have tunable filters to make astronomical observations.

FIRST: Far-Infrared and Sub-millimetre Space Telescope

FM: Flight Model

FOC: Faint Object Camera (HST)

Forward Scattering: Reflecting light approximately away from the source.

FOT: Flight Operations Team

FOV: Field of View

FPA: Focal Plane Array

FS: Fowler Sampling

FSM: Fast Steering Mirror

FSW: Flight Software

FWHM: Full Width at Half Maximum

FY: Fiscal Year

GAIA: Global Astrometric Interferometer for Astrophysics

Galaxy: A huge assembly of stars, gas and dust bound together by gravity.

GCR: Galactic Cosmic Ray

General Relativity: The ideas developed by Albert Einstein that mass and energy determine the geometry of spacetime and that the curvature of this spacetime manifests itself as what we call gravitational forces.

Geo-: Prefix referring to the Earth.

Geocentric: Earth centered.

GGS: Global Geospace Science

GHRS: Goddard High Resolution Spectrometer (HST)

GINGA: Japanese X-Ray Satellite

Globular Cluster: A gravitationally bound system of several hundred thousand to one million stars thought to have all formed at the same time.

GMT: Greenwich Mean Time

GOES: Geostationary Operational Environmental Satellite

GPS: Global Positioning System

Gravity: The force of attraction between masses.

GRB: Gamma Ray Burst

Great Red Spot: Jupiter's very large anti-cyclonic (high pressure) storm, which is akin to a hurricane on Earth. Three Earths would fit within its boundaries - and it has persisted for at least the 400 years that humans have observed it through telescopes..

GRO: Gamma Ray Observatory (see CGRO)

GSFC: Goddard Space Flight Center

GTO: Geo-Transfer Orbit

Halley's Comet: A specific bright comet, visible to the naked eye, whose path we can predict.

HARD: High Accuracy Reflector Development

HDF: Hubble Deep Field

Helio-: Prefix referring to the Sun.

Heliocentric: Centered on the Sun.

Hertzsprung-Russell Diagram: A graphical representation of the classification of stellar types according to temperature and brightness. Physical properties of stars are related to their position on the diagram. Therefore, changes in the positions of stars on the diagram can be used to trace their evolution.

HGA: High Gain Antenna

HST: Hubble Space Telescope

HSTS: Heuristic Scheduling Testbed System

Hubble Constant: This number relates the distances of galaxies to their recession velocity and represents the rate at which the universe is currently expanding.

I/F: Interface

I&C: Instrumentation and Communication

I&T: Integration and Test

IAS: Institut d'Astrophysique Spatiale, Orsay (France)

IAU: International Astronomical Union

IDT: Investigation Definition Team

IFSI: Istituto Fisica Spazio Interplanetario (Italy)

IFTS: Imaging Fourier Transform Spectrometer

IGPP: Institute of Geophysics and Planetary Physics

IKI: Space Research Institute of the Russian Academy of Science

IMOS: Simulation platform for structural, optical & AACS/FSW interactions

Inclination: Tilt or angle. When used with respect to an orbit, the angle between the orbital plane of a revolving body and some fundamental plane, usually the plane of the celestial equator.

Infrared: Electromagnetic radiation whose wavelength is longer than the longest visible red but shorter than radio waves.

INTA: Instituto Nacional de Tecnica Aerospacial (Spain)

Interferometery: The location and examination of sources of electromagnetic radiation through the simultaneous use of two or more separated telescopes. Interferometers produce overlapping wave patterns from the radiation. These patterns are studied to determine the brightness and angular structure of the emitting source.

Ion : An atom or molecular fragment that has a positive electrical charge due to the loss of one or more electrons. The simplest ion is the hydrogen nucleus, a single proton.

IPAC: Infrared Processing Analysis Centre

IR: Infrared

IPDT: Integrated Product Development Team

IPT: Integrated Product Team

IRAF: Image Reduction & Analysis Facility

IRAS: Infrared Astronomy Satellite

IRD: Interface Requirements Document

IRMB: Institut Royal Meteorologique de Belgique

ISAS: Institute of Space and Astronautical Science (part of the Japanese Aerospace Exploration Agency)

ISIM: Integrated Science Instrument Module

ISIS: Inflatable Sunshield in Space

ISM: Interstellar Medium

ISO: Infrared Space Observatory

ITAR: International Traffic in Arms Regulations

IUE: International Ultraviolet Explorer

IUEFA: IUE Final Archive

JAXA: Japan Aerospace Exploration Agency

JCMT: James Clerk Maxwell Telescope

Jovian Planet: Any of the four biggest planets: Jupiter, Saturn, Uranus, and Neptune.

JPL: Jet Propulsion Laboratory

JSC: Lyndon B. Johnson Space Center

JWST: James Webb Space Telescope

Kelvin: Absolute temperature scale measure. Absolute zero, or 0 Kelvin corresponds to -273 degrees Celsius.

Kiloparsec (kpc): A disatance of one thousand parsecs (see: Parsec)

KSC: Kennedy Space Center

Kuiper Belt: A field of icy, comet-like bodies extending from the orbit of Neptune out to about 7 billion miles (10 billion km) from the Sun.

Kuiper Belt Object (KBO): One of the icy, comet-like bodies residing in the Kuiper Belt.

L2 Point: A location roughly 1.5 million km (1 million miles) in the anti-Sun direction of the Earth. An object at the L2 point will tend to follow the Earth as it goes around the Sun.

Lagrangian or Lagrange Point: Lagrange Points mark positions where the gravitational pull of the two large masses precisely equals the centripetal force required to rotate with them. Used for positioning satellites in space, where minimum fuel will be required to maintain a stable orbit.

LAMP: Large Advanced Mirror Program

LaRC: Langley Research Center

LBV: Luminous Blue Variable

LDEF: Long Duration Exposure Facility

Leading Side: For a satellite that keeps the same face toward the planet, the hemisphere that faces forward, into the direction of motion.

Light: Electromagnetic radiation. Commonly used to describe that which is visible to the eye.

Light year: The distance light travels in a vacuum in one year; equal to 9.46x1015 meters.

LISA: Laser Interferometer Space Antenna

LMC: Large Magellanic Cloud

LMCo: Lockheed Martin Corporation

LMXRB: Low Mass X-ray Binary

LOS: Line of Sight or Loss of Signal

LPSP: Laboratoire de Physique Stellaire et Planetaire (France)

LTE: Local Thermal Equilibrium

Lunar: Referring to the moon.

Magnetic field: A region of space near a magnetized body where magnetic forces can be detected.

Magnetopause: The boundary of the magnetosphere, lying inside the bow shock.

Magnetosphere: The region surrounding a planet within which the planetary magnetic field dominates and charged particles can be trapped.

MAP: Microwave Anisotropy Probe (now WMAP)

MAS: Milli-arcseconds

MDS: Mission Data System

Mean: Synonym for mathematical average.

Megaparsec (Mpc): One million parsecs (see: parsec)

Meteor: The luminous phenomenon seen when a meteoroid enters the atmosphere, commonly known as a shooting star.

Meteorite: A part of a meteoroid that survives entry into the Earth's atmosphere.

Meteoroid: A small rock in space.

MFSC: Marshall Space Fight Center

MHD: Magneto-hydrodynamics

Microdynamics: The physics of very small forces

Micron: A distance of 1/1,000,000th of a meter, roughly 1/25,000th of an inch. (Also called a micrometer, abbreviated µm).

Mid Infrared: The the middle part of the range of infrared.

MIRI: The JWST Mid Infrared Instrument. MIRI will observe lower energy (longer wavelength) light than the other instruments.

MLI: Multilayer Insulation

MMS: Matra Marconi Space, also Magnetospheric Multiscale Mission

MOS-CCD: Metal Oxide Semiconductor - Charge Coupled Device

MPE: Max-Planck-Institut fur Extraterrestrische Physik

MPI: Max-Planck-Institut (Germany)

MPS: Mission Planning and Scheduling system

MTF: Modulation Transfer Function

NASA: National Aeronautics and Space Administration

NASDP: NGST Adaptive Scheduler Demonstration Prototype

NCC: Network Control Center (NASA GSFC)

NEA: Noise Equivalent Angle

Near Infrared: The range of infrared radiation nearest to the range of human vision.

NEPS: Noise Equivalent Point Source

Newton: A unit of force that is a size such that a body of one kilogram under it effects would accelerate one meter per second per second.

NGC: New General Catalogue

NG: Northrop Grumman (JWST Observatory prime contractor).

NGST: Next Generation Space Telescope (original name of JWST)

NICMOS: Near-Infrared Camera and Multi-Object Spectrometer (HST)

NIEL: Non-Ionizing Energy Loss

NIR: Near Infrared

NIRCam: The JWST Near Infrared Camera instrument. NIRCam will primarily take "pictures" of the sky.

NIRSpec: The JWST Near Infrared Spectrograph instrument. NIRSpec will measure spectra of objects in the sky.

NLR: Narrow Line Region

NMSD: NGST Mirror System Demonstrator

NOAA: National Oceanographic and Atmospheric Administration

NOT: Nordic Optical Telescope

NRA: NASA Research Assignment

NRAO: National Radio Astronomy Observatory

NSI: NASA Science Internet

NSSDC: National Space Science Data Center (at GSFC)

OFLS: Off-Line System (AXAF)

Omega: In astronomy, omega is a dimensionless number that measures the ratio of the density of the universe to the critical density (the density to close the universe).

Oort Cloud: An as-yet undetected pool of small bodies in the outermost regions of the Solar System, perhaps extending as much as 1/10th of a light year from the Sun. Long-period comets are believed to originate in the Oort Cloud.

OPD: Optical Path Difference

OR: Observation Request

Orbit: The path of an object that is moving around a second object or point.

OS: Operating System

OTA: Optical Telescope Assembly

PAH: Polycyclic Aromatic Hydrocarbon

Parallax: The change in an object's apparent position when viewed from two different locations.

Parsec (pc): Commonly used unity of distance for astronomy. Equal to 3.26 light years, it is actually the distance an object would have to be from Earth for its parallax to be 1 second of arc.

PASS: POCC Applications Support Software (HST)

PCD: Photon Counting Detector

PEP: Proposal Entry Processor (HST)

Periapsis: Low point of an orbit.

Perturbation: A small disturbing effect

Phase angle: The angle in which waves come to a body.

Photometry: The measurement of light intensities.

Photon: a discrete packet of electromagnetic energy.

PI: Principal Investigator

Plasma: A fourth state of matter - not a sold, liquid, or gas. In a plasma, the electrons are pulled free from the atoms and can move independantl. The individual atoms are charged, though the total number of positive and negative charges is equal, maintaining an overall electrical neutrality.

PLM: Payload Module

PM: Primary Mirror

PNAR: Preliminary Non-Advocate Review

POCC: Project Operations Control Center

Primitive: Used in a chemical sense, it indicates an unmodified material representative of the original composition.

PROM: Programmable Read-Only Memory

PSF: Point Spread Function

QE: Quantum Efficiency

QPO: Quasi Periodic Oscillations

QSO: Quasi Stellar Object. They are intense, point-like sources of radiation (often from radio through gamma rays), characterized by high redshifts. The term QSO used to describe both radio-loud and radio-quiet classes of objects.

Quasar: Quasar is a contraction of "quasi stellar radio source". Since it turns out that not all of the objects described as quasars are sources of radio radiation, the term QSO was invented, to refer to both the radio-loud and radio-quiet objects.

R&D: Research and Development

Radiation: Electromagnetic energy, photons

Radiation Belts: More intense regions of charged particles in a magnetosphere; the belts contain ions and electrons.

RAL: Rutherford Appleton Laboratory (UK)

RAX: Remote Agent Experiment (DS-1)

Resolution: Ability to distinguish detail, usually expressed in terms of the size of the smallest features that can be distinguished.

Resonance: In astronomy, a relationship in which the orbital period of one body is related to that of another by a simple integer fraction, such as 1/2, 2/3, 3/5.

Retrograde: Backwards; as applied to an orbit, moving in the opposite sense from the great majority of solar system bodies.

Revisits: As a nound, the number of separate times that the JWST must observe a specific target to accomplish science goals outlined in the Design Reference Mission

RF: Radio Frequency

RFP: Request For Proposals

RMS: Remote Manipulator System (Space Shuttle)

RPS-2: Remote Proposal Submission System - Second Generation (HST)

RQE: Responsive Quantum Efficiency

RTG: Radioisotope Thermal Generator

SAO: Smithsonian Astrophysical Observatory

SASC: Science Analysis Support Centre

Satellite: A body that revolves around a larger body.

SAX: Satellite per Astronomia in raggi X (Italy/The Netherlands)

SCA: Sensor Chip Array

SED: Spectral Energy Distribution

SERC: Science & Engineering Council (UK)

SES: Systems Engineering Simulator (JSC)

Shroud, Rocket: The fairing of the rocket that contains the payload. The limitations of available shroud diameters has a direct impact on the size and packaging of the JWST.

SI: Science Instrument

SIRTF: Space Infrared Telescope Facility (now Spitzer Space Telescope)

SMS: Science Mission Schedule

SN: Supernova

SNR: Supernova Remnant

SOC: Science Operations Centre

Solar Nebula: The large cloud of gas and dust from which the Sun and planets condensed 4.6 billion years ago.

Solar Wind: The charged particles (plasma), primarily protons and electrons, that are emitted from the Sun and stream outward throughout the solar system at speeds of hundreds of kilometers per second.

SOT: Science Operations Team

Space Density: From the design reference mission: The expected frequency of objects in space measured in number of objects per square minutes of arc on the sky.

Spacetime: A system for looking at the universe as one in which the three spatial dimensions are unified with the time dimension.

Spectroscopy: The use of spectrum analysis.

Spectrum: A particular distribution of wavelengths or frequencies and energy. A rainbow is a naturally-occurring spectrum of sunlight.

SPSS: Science Planning and Scheduling System (HST)

SR: Strehl Ratio

SSM: Space Support Module

ST-ECF: Space Telescope - European Coordinating Facility

STEP: Satellite Test of the Equivalence Principle

STIS: Space Telescope Imaging Spectrograph

STJ: Superconducting Tunnel Junction

STS: Space Transportation System

STScI: Space Telescope Science Institute

STSP: Solar Terrestrial Science Programme

Supernova: The explosion of a massive star

SUTR: Sample Up The Ramp

SWT: Science Working Team

SZ: Sunyaev-Zeldovich Effect

TDRS: Tracking and Data Relay Satellite

TDRSS: Tracking and Data Relay Satellite System

Telemetry: Radio signals from a spacecraft used to encode and transmit data to a ground station.

TID: Total Ionizing Dose

TOO: Target of Opportunity

Torus: Solid geometrical figure with the shape of a doughnut or innertube.

TPF: Terrestrial Planet Finder

TRANS: Transformation expert system (HST)

TSU APT: Tennessee State University Automatic Photoelectric Telescopes

ULE: Ultra Low Expansion

Ultraviolet (UV): Electromagnetic radiation whose wavelength is shorter than visible light but longer than X-rays.

VILSPA: Villafranca Satellite Tracking Station

Visible Light: Electromagnetic radiation whose wavelength is between 3.5x10-7 and 8.0x10-7 meters.

VLA: Very Large Array

VLBI: Very Long Baseline Interferometry

VRTX: Versatile Real Time Executive

VSIM: "Prescription Retrieval" software that measures alignment errors

VTT: Vacuum Tower Telescope

Wavelength: The distance between two successive peaks or troughs of a wave.

WCT: Wave Front Control Testbed

WFC: Wave Front Control

WFE: Wave Front Error

WFPC2: Wide Field Planetary Camera 2 (HST)

WFS&C: Wave Front Sensing & Control

WIRE: Wide-Field Infrared Explorer

WLI: White Light Interferometry

WMAP: Wilkinson Microwave Anisotropy Probe

WWW: World Wide Web

XMM: X-ray Multi-Mirror Mission (Cornerstone)

X-ray: High energy electromagnetic radiation with a wavelength of about 10-10 meters.

XTE: X-Ray Timing Explorer (now Rossi X-ray Timing Explorer or RXTE)

ZAMS: Zero Age Main Sequence

Zodiac: In astronomy, the region of the sky through which the planets are observed to move.