Term Index (J)
- J:
- J band:
- infrared (IR): electromagnetic radiation, wavelength 0.74-300 micrometers
- J coefficients:
- J2: geopotential coefficient regarding a planet's oblateness
- J designator: designator using equatorial coordinates at year 2000
- J-MAG:
- JUICE: mission to Jupiter in development
- J-type shock:
- shock wave: abrupt propagating disturbance in a fluid
- J1407: star orbited by a companion with a ring system
- J1713-0747: binary system with millisecond pulsar and white dwarf
- J2:
- J2000:
- J2000 epoch:
- epoch: when an object was at a particular set of celestial coordinates
- J2000 equinox:
- equinox: times when tilt of Earth is neither toward or away from the Sun
- J2000.0:
- epoch J2000.0: noon 1/1/2000 GMT as used as a time reference
- terrestrial time (TT): current measure of time for astronomical observations on Earth
- J2000.0 epoch:
- epoch: when an object was at a particular set of celestial coordinates
- J2000.0 equinox: equinox as of the J2000.0 epoch used as a positional reference
- equinox: times when tilt of Earth is neither toward or away from the Sun
- J20000 epoch:
- epoch: when an object was at a particular set of celestial coordinates
- J2: geopotential coefficient regarding a planet's oblateness
- J3:
- J2: geopotential coefficient regarding a planet's oblateness
- Jacobi constant:
- Jacobi integral: method of solving some three-body problems
- Jacobus Kapteyn Telescope:
- Jacoby:
- JADE:
- JaFu:
- James Clerk Maxwell Telescope (JCMT): far-infrared telescope in Hawaii
- James Webb Space Telescope (JWST): future space-based 6.5 meter infrared telescope
- Jansky:
- jansky (Jy): unit of measurement of spectral flux density
- Very Large Array (VLA): radio telescope in New Mexico
- JANUS:
- JUICE: mission to Jupiter in development
- Japan:
- Japan Aerospace Exploration Agency (JAXA): Japan agency includes astronomical research
- Japanese:
- AKARI: Japanese space infrared telescope
- ASTRO-H: Japanese space X-ray telescope
- MAXI: Japanese X-ray camera on the International Space Station
- SELENE: 2007-2008 Japanese lunar probe
- Yohkoh: 1990s Japanese solar observatory spacecraft
- JAXA:
- AKARI: Japanese space infrared telescope
- ASCA: 1990s Japanese space X-ray telescope
- ASTRO-H: Japanese space X-ray telescope
- BepiColombo: mission to Mercury
- Ginga: 1980s Japanese space X-ray telescope
- Japan Aerospace Exploration Agency (JAXA): Japan agency includes astronomical research
- LiteBIRD: planned spacecraft to map CMB polarization
- MMX: Japanese probe to bring back a sample of a Martian moon
- SELENE: 2007-2008 Japanese lunar probe
- SPICA: plan for a future space IR telescope
- Suzaku: space X-ray telescope
- Yohkoh: 1990s Japanese solar observatory spacecraft
- JBO:
- JC:
- JCM:
- JCMT:
- JCMT dust and gas In Nearby Galaxies Legacy Exploration:
- JINGLE: survey of dust and gas in galaxies
- JD:
- Julian date (JD): time in days since noon UT November 24 4714 BC Gregorian
- JDEM:
- JDN:
- Julian date (JD): time in days since noon UT November 24 4714 BC Gregorian
- Jeans criterion:
- Jeans length: critical radius below which gravity will collapse a cloud
- Jeans density:
- Jeans length: critical radius below which gravity will collapse a cloud
- Jeans escape: type of ongoing escape of gas particles from atmosphere
- Jeans escape parameter:
- Jeans instability:
- Jeans length: critical radius below which gravity will collapse a cloud
- Jeans length: critical radius below which gravity will collapse a cloud
- Jeans mass:
- Jeans length: critical radius below which gravity will collapse a cloud
- Jeans parameter (λ): ratio measuring a tendency of an atmosphere to escape
- Jeans swindle:
- Jeans length: critical radius below which gravity will collapse a cloud
- JEDI:
- JEF:
- jellyfish galaxy: galaxy with a gas tail including star formation
- JEM-X:
- INTEGRAL: European gamma ray observatory-satellite
- jet: stream of matter from an astronomical body
- 3C 273: first quasar discovered
- 3C 279: striking variable quasar
- 3C 303: Seyfert galaxy
- 3C 348: giant elliptical radio galaxy
- 3C 9: first quasar discovered
- Cygnus A (3C 405,QSO B1957+405): early-discovered radio galaxy and quasar
- M87: supergiant elliptical galaxy in local universe
- superrotating wind: wind traveling in the same direction as the planet is rotating
- zonal flow: east-west air circulation
- zone: apparent "horizontal" band in an atmosphere
- jet current: electric current within a plasma jet
- jet stream:
- jet: stream of matter from an astronomical body
- superrotating wind: wind traveling in the same direction as the planet is rotating
- thermal wind: wind from pressure and the Coriolis force varying with altitude
- zonal flow: east-west air circulation
- JET-X:
- Spektr-RG (SRG, SXG): Russian-German X-ray observatory launched in 2019
- jets:
- bipolar outflow: streams of matter from the poles of a protostar
- Herbig-Haro object (HH,HHO): illuminated nebula from colliding jets
- jet current: electric current within a plasma jet
- mass loading: moving gas gaining mass from clouds or stars
- microquasar: stellar-sized black hole with quasar-like activity
- quasar (QSO): distant, bright object that appears something like a star
- relativistic beaming: directional relativistic effect on light from relativistic speeds
- JFC:
- JHK:
- JHK photometric system (JHK): system to classify stars according to near-infrared colors
- JINGLE: survey of dust and gas in galaxies
- JIRAM:
- JKT:
- Jodrell Bank Experimental Station:
- Jodrell Bank Mark II:
- Mark II (MKII): 38 m radio telescope in England
- Jodrell Bank Observatory (JBO): radio observatory in England
- Mark II (MKII): 38 m radio telescope in England
- MERLIN: VLBI array spread across England
- Johannsen-Psaltis metric (JP metric): metric template allowing metrics to be written as a general expansion
- Johannsen-Psaltis spacetime:
- John A. Galt Telescope:
- Johns Hopkins University:
- Johnson system:
- Johnson-Cousins system:
- Johnson-Morgan System:
- Johnson-Nyquist noise:
- thermal noise: noise inherent in electronic component warmer than absolute zero
- JOI:
- Joint Dark Energy Mission:
- joule (J): SI unit of energy
- Joule heating:
- Ohmic heating: heating resulting from an electric current through a material
- journal:
- Jovian planet:
- JOY:
- JP metric:
- JP spacetime:
- JPA:
- Giotto: 1980s space mission carrying out a Comet Halley flyby
- JPL:
- JSP:
- Juchert:
- JUICE: mission to Jupiter in development
- Julian calendar: calendar of 365 days and a leap day once every four years
- Julian date (JD): time in days since noon UT November 24 4714 BC Gregorian
- Julian day:
- Julian date (JD): time in days since noon UT November 24 4714 BC Gregorian
- Julian day number:
- Julian date (JD): time in days since noon UT November 24 4714 BC Gregorian
- Julian year:
- Julian calendar: calendar of 365 days and a leap day once every four years
- Julian date (JD): time in days since noon UT November 24 4714 BC Gregorian
- sidereal: relative to the fixed position of the stars
- Juno: mission to Jupiter
- Juno Orbit Insertion:
- Juno Vesta:
- asteroid: minor planet without comet characteristics
- JunoCam:
- Jupiter: largest planet in the solar system
- Callisto: well-known Jupiter moon
- Europa: well-known Jupiter moon
- Europa Clipper: planned Europa space probe
- Europa Lander: plan for a mid 2020s Europa probe landing on the surface
- Galileo: circa 1990s space mission to Jupiter
- Ganymede: well-known Jupiter moon
- helium rain: possible source of heat in giant planet atmospheres
- Io: well-known Jupiter moon
- JUICE: mission to Jupiter in development
- Juno: mission to Jupiter
- liquid planet: planet consisting of liquid
- ring system: disk or set of rings orbiting a planet
- shepherd moon: small moon at outer edge of a ring
- Voyager: space probes to observe planets and the edge of the solar system
- Jupiter I:
- Io: well-known Jupiter moon
- Jupiter Icy Moons Explorer:
- JUICE: mission to Jupiter in development
- Jupiter II:
- Europa: well-known Jupiter moon
- Jupiter III:
- Jupiter IV:
- Jupiter mass:
- mass: object's quality that determines the effects of forces and gravity
- Jupiter Orbiter Probe:
- Galileo: circa 1990s space mission to Jupiter
- Jupiter Trojan:
- Jupiter-family comet:
- Jupiters:
- JVLA:
- JW:
- JWST:
- Jy:
- jansky (Jy): unit of measurement of spectral flux density
Index