The date on which the day and night have exactly the same length. Contrary to the widespread statement, the day and night are not equal at the → equinox. The higher the → latitude, the greater the difference. In fact the day and night lengths are equal at the equinox only if the strict theoretical definition is used, according to which sunset and sunrise are the moments when the center of the Sun crosses the → horizon. There are two reasons for this inequality: 1) The Sun is a disk, not a point source. It is about 30 arc minute wide, hence sunrise corresponds to the moment the top of the disk (and not its center) emerges out of the horizon. Similarly, sunset is when the last part of the disk sinks below the horizon. The Sun takes about a minute to move from its center to its edge (the Earth rotates about 1 degree in 4 minutes). This sums to two minutes (a minute for sunset and a minute for sunrise) that adds to 4 minutes in the total difference. 2) The atmosphere acts as a lens, and slightly bends the Sun's rays because of the → atmospheric refraction. When we look at the setting Sun, the fact is that it was already set. Unlike the equinox, which is a fixed date all-over the globe, the date of the equilux is dependent upon the → latitude of the observer. Between the poles and about 20 degrees latitude, it is generally a few days before the → vernal equinox or a few days after the → autumnal equinox .
The amount of energy, fluid, or particles passing in a given direction in a unit of time.
O.Fr. flux, from L. fluxus, p.p. of fluere "to flow," PIE base *bhleug- (cf. L. flumen "river;" Gk. phluein "to boil over, bubble up," phlein "to abound").
Šâr "outpouring of water, wine, etc.," šâridan "to flow (as rivers), with a great noise; to pour," âbšâr "waterfall;" saršâr "overflowing; brim-full;" Ossetic ægzælyn "to pour down;" Pashto zγâstəl/zγâl- "to swim;" Av. γžār- "to flow;" cf. Skt. ksar- "to flow;" Gk. phtheirein "to destroy, perish."
Fr.: calibration de flux
The → calibration of the flux received by a detector in terms of absolute units.
Fr.: densité de flux
Flux of radiation that falls on a detector per unit surface area of the detector per unit bandwidth of the radiation per unit time.
Fr.: unité de flux
In radio astronomy, same as → jansky (symbol Jy), a unit of electromagnetic flux equivalent to 10-26 watts per square meter per Hertz.
In Newton's work on → calculus, the rate of change of a fluent (i.e. a flowing quantity), today commonly known as → variable. For a fluent x, the fluxion is denoted dx/dt. An obsolete mathematical term.
šâr-e tâbeši (#)
Fr.: flux lumineux
A measure of the rate of flow of luminous energy, evaluated according to its ability to produce a visual sensation. It is measured in lumens.
SI unit of illumination equal to a luminous flux of 1 lumen per square meter. SI unit of luminous incidence or illuminance, equal to 1 lumen per square meter.
From Gk. lux "light," → lumen.
šâr-e meqnâtisi (#)
Fr.: flux magnétique
A measure of the quantity of magnetism or magnetic field. It is the number of lines of force passing normally through a given area. Magnetic flux is a scalar quantity defined as the surface integral of the → magnetic flux density. It is usually denoted by the Greek letter Φ and its SI unit is the → weber.
magnetic flux density
cagâli-ye šâr-e meqnâtisi (#)
Fr.: densité du flux magnétique
A vector quantity measuring the strength and direction of the magnetic field. It is the → magnetic flux per unit area of a magnetic field at right angles to the magnetic force. Magnetic flux density is expressed in → teslas. Also called → magnetic induction.
Fr.: flux de météorites
The total mass of extraterrestrial objects that land on Earth during a given time period. The meteorite flux is currently estimated to be about 107 to 109 kg yr-1. Much of this material is dust-sized objects called → micrometeorites.
Pollux (β Geminorum)
The brightest star in the constellation → Gemini despite its designation as β. Also known as HR 2990 and HD 62509. Pollux lies about 4 degrees apart from the blue star → Castor with which it has no physical connection. Pollux is an orange-red star with a → visual magnitude 1.14 (B - V = +1.00) located about 34 → light-years away. It is a → giant star of → spectral type K0 III, with a mass of 2 Msun, a radius of about 10Rsun, a luminosity of 43 Lsun, and an → effective temperature of 4666 K. Pollux has a large planet, → Pollux b, with a mass of at least 2.3 times the mass of Jupiter.
Pollux, Gk. Polydeucus is one of the "Heavenly Twins," brother to → Castor, sons of Leda and Zeus.
Pollux, loan from L., as above. It has a too long Ar. name:
Fr.: Pollux b
An → extrasolar planet orbiting the bright star → Pollux (β Gem). It lies approximately 34 → light-years away in the constellation → Gemini. Called also → Thestias, it has a mass of at least 2.30 → Jupiter mass, and orbits Pollux at a distance of about 1.64 → astronomical units once every 590 days.
šâr-e tâbeši (#)
Fr.: flux radiatif
Rate of flow of energy as → radiation.
Fr.: flux radiatif
The radiative energy per unit time and unit area.
Fr.: flux radio
Total radiation in radio wavelengths going out from the 2π solid angles of a hemisphere. → flux.
radio flux density
cagâli-ye šârr-e râdioyi
Fr.: densité de flux radio
tube of flux
Fr.: tube de flux
Bundles of lines of electrical intensity into which the vector field of electrical force can be divided. Same as tube of force, field tube.