An Etymological Dictionary of Astronomy and Astrophysics

An energy schematic representing the → electronic states
of a → molecule and the → transitions between them. The vertical axis shows energies whereas → energy states are grouped horizontally according to their spin → multiplicity. Radiation-less transitions are symbolized by usual arrows, while → radiative transitions are represented by wavy arrows. The vibrational ground states of each electronic state are indicated with thick lines and the higher → vibrational states with thinner lines.

See also: Named after Aleksander Jablonski (1898-1980), a Polish physicist who was an expert in the field of luminescence and atomic optics; → diagram.

An energy schematic representing the → electronic states
of a → molecule and the → transitions between them. The vertical axis shows energies whereas → energy states are grouped horizontally according to their spin → multiplicity. Radiation-less transitions are symbolized by usual arrows, while → radiative transitions are represented by wavy arrows. The vibrational ground states of each electronic state are indicated with thick lines and the higher → vibrational states with thinner lines.

See also: Named after Aleksander Jablonski (1898-1980), a Polish physicist who was an expert in the field of luminescence and atomic optics; → diagram.

The integral admitted by the equations of a body of infinitesimal mass moving under the → gravitational attractions of two massive bodies, which move in circles about their → center of gravity. The Jacobi integral is the only known conserved quantity for the circular → restricted three-body problem.

In the co-rotating system it is expressed by the equation: (1/2) (x^·2 + y^·2

• z^·2) = U - C_J, where the dotted coordinates represent velocities, U is potential energy, and C_J the constant of integration (→ zero-velocity surface). The Jacobi integral has been used for two different purposes:

1. to construct surfaces of zero velocity which limit the regions of space in which the small body, under given initial conditions, can move, and 2) to derive a criterion (→ Tisserand’s parameter) for re-identification of a → comet whose orbit has suffered severe perturbations by a planet. Also known as Jacobi constant.

See also: Named after Karl Gustav Jacobi (1804-1851), a German mathematician who did important work on elliptic functions, partial differential equations, and mechanics; → integral.

The integral admitted by the equations of a body of infinitesimal mass moving under the → gravitational attractions of two massive bodies, which move in circles about their → center of gravity. The Jacobi integral is the only known conserved quantity for the circular → restricted three-body problem.

In the co-rotating system it is expressed by the equation: (1/2) (x^·2 + y^·2

• z^·2) = U - C_J, where the dotted coordinates represent velocities, U is potential energy, and C_J the constant of integration (→ zero-velocity surface). The Jacobi integral has been used for two different purposes:

1. to construct surfaces of zero velocity which limit the regions of space in which the small body, under given initial conditions, can move, and 2) to derive a criterion (→ Tisserand’s parameter) for re-identification of a → comet whose orbit has suffered severe perturbations by a planet. Also known as Jacobi constant.

See also: Named after Karl Gustav Jacobi (1804-1851), a German mathematician who did important work on elliptic functions, partial differential equations, and mechanics; → integral.

→ Jacobian determinant, → Jacobian matrix.

See also: Named after Karl Gustav Jacobi (1804-1851), a German mathematician who did important work on elliptic functions, partial differential equations, and mechanics. The “Jacobian” first appeared in an 1815 paper of the French mathematician Augustin Louis Cauchy (1789-1857), but Jacobi did write a detailed memoir about it in 1841.

→ Jacobian determinant, → Jacobian matrix.

See also: Named after Karl Gustav Jacobi (1804-1851), a German mathematician who did important work on elliptic functions, partial differential equations, and mechanics. The “Jacobian” first appeared in an 1815 paper of the French mathematician Augustin Louis Cauchy (1789-1857), but Jacobi did write a detailed memoir about it in 1841.

The determinant of a → Jacobian matrix formed by the n² → partial derivative s of n functions of n variables.

See also: → Jacobian; → determinant.

The determinant of a → Jacobian matrix formed by the n² → partial derivative s of n functions of n variables.

See also: → Jacobian; → determinant.

In → vector calculus, the matrix of all → first-order partial derivatives of a vector-valued → function.

See also: → Jacobian; → matrix.

In → vector calculus, the matrix of all → first-order partial derivatives of a vector-valued → function.

See also: → Jacobian; → matrix.

An Iranian solar calendar, based on two successive passages of the Sun through the true → vernal equinox. It results from a reform undertaken by a group of astronomers led by Omar Khayyam (A.D. 1048-1131). The current → Iranian calendar is an improved version of the Jalali calendar.

See also: Jalali, from the name of the ruler Jalâleddin Malek Šâh
of the Saljuqid dynasty, who ordered the reform; → calendar.

An Iranian solar calendar, based on two successive passages of the Sun through the true → vernal equinox. It results from a reform undertaken by a group of astronomers led by Omar Khayyam (A.D. 1048-1131). The current → Iranian calendar is an improved version of the Jalali calendar.

See also: Jalali, from the name of the ruler Jalâleddin Malek Šâh
of the Saljuqid dynasty, who ordered the reform; → calendar.

A large, infrared space telescope with a mirror 6.55 m in diameter, scheduled for launch in 2018. JWST’s instruments will work primarily in the infrared range of the electromagnetic spectrum, with some capability in the visible range (0.6 to 28 μm). The scheduled instruments are Near IR Camera (NIRCam, field of 2.2 x 4.4 arcmin, wavelength range 0.6-5 μm), Near IR Spectrograph (NIRSpec, 3.5 x 3.5 arcmin, 0.6-5 μm, resolving powers of ~ 100, ~1000, and ~3000), Mid IR Instrument (MIRI, 1.4 x 1.9 arcmin, 5-27 μm, R ~ 3000), and Fine Guidance Sensor (FGS, 2.3 x 2.3 arcmin, 0.6-5 μm, R ~ 100). The successor to the → Hubble Space Telescope will be placed in an orbit about 1.5 million km from the Earth, at the → Lagrangian point L2. The JWST project is a → NASA-led international collaboration with the → European Space Agency and the Canadian Space Agency. The scientific goals of JWST can be grouped under four broad topics: first light after the Big Bang; galaxy formation; birth of stars and protoplanetary systems; and planetary systems and the origins of life.

See also: Named in honor of James E. Webb (1906-1992), who headed NASA from 1961 to 1968, overseeing all the manned launches in the Mercury through Gemini programs, until before the first manned Apollo flight; → space; → telescope.

A large, infrared space telescope with a mirror 6.55 m in diameter, scheduled for launch in 2018. JWST’s instruments will work primarily in the infrared range of the electromagnetic spectrum, with some capability in the visible range (0.6 to 28 μm). The scheduled instruments are Near IR Camera (NIRCam, field of 2.2 x 4.4 arcmin, wavelength range 0.6-5 μm), Near IR Spectrograph (NIRSpec, 3.5 x 3.5 arcmin, 0.6-5 μm, resolving powers of ~ 100, ~1000, and ~3000), Mid IR Instrument (MIRI, 1.4 x 1.9 arcmin, 5-27 μm, R ~ 3000), and Fine Guidance Sensor (FGS, 2.3 x 2.3 arcmin, 0.6-5 μm, R ~ 100). The successor to the → Hubble Space Telescope will be placed in an orbit about 1.5 million km from the Earth, at the → Lagrangian point L2. The JWST project is a → NASA-led international collaboration with the → European Space Agency and the Canadian Space Agency. The scientific goals of JWST can be grouped under four broad topics: first light after the Big Bang; galaxy formation; birth of stars and protoplanetary systems; and planetary systems and the origins of life.

See also: Named in honor of James E. Webb (1906-1992), who headed NASA from 1961 to 1968, overseeing all the manned launches in the Mercury through Gemini programs, until before the first manned Apollo flight; → space; → telescope.

The unit of → radio flux density in → radio astronomy, equivalent to 10^-26→ watts per square meter per → hertz.

See also: Named in 1973 by the International Astronomical Union in honor of Karl Guthe Jansky (1905-1950),
an American engineer of Czech descent who first identified radio waves
from beyond the Solar System.

The unit of → radio flux density in → radio astronomy, equivalent to 10^-26→ watts per square meter per → hertz.

See also: Named in 1973 by the International Astronomical Union in honor of Karl Guthe Jansky (1905-1950),
an American engineer of Czech descent who first identified radio waves
from beyond the Solar System.

The sixth of Saturn’s known satellites. With a mean diameter of about 178 km it orbits Saturn at a distance of 150,000 km. Discovered by the French astronomer Audouin Dollfus (1924-) in 1966.

See also: Janus was the god of gates and doorways in Roman mythology. He was also thought to represent beginnings, hence he lent his name to January, the first month of the year. He was depicted with two faces looking in opposite directions.

The sixth of Saturn’s known satellites. With a mean diameter of about 178 km it orbits Saturn at a distance of 150,000 km. Discovered by the French astronomer Audouin Dollfus (1924-) in 1966.

See also: Janus was the god of gates and doorways in Roman mythology. He was also thought to represent beginnings, hence he lent his name to January, the first month of the year. He was depicted with two faces looking in opposite directions.

A colored form of natural silica, SiO₂, which is a precious stone.

Etymology (EN): M.E. jaspe, jaspre, from M.Fr., O.Fr. jaspe,
from L. iaspidem (nominative iaspis), from Gk. iaspis “jasper,” via an Oriental language, probably an Eastern Iranian language, see below.

Etymology (PE): Yašm, variants, yasp, yasb, yašf “jasper;” Sogd. iešp “jasper,” iešpênê “of jasper, crystalline.”

A colored form of natural silica, SiO₂, which is a precious stone.

Etymology (EN): M.E. jaspe, jaspre, from M.Fr., O.Fr. jaspe,
from L. iaspidem (nominative iaspis), from Gk. iaspis “jasper,” via an Oriental language, probably an Eastern Iranian language, see below.

Etymology (PE): Yašm, variants, yasp, yasb, yašf “jasper;” Sogd. iešp “jasper,” iešpênê “of jasper, crystalline.”