An Etymological Dictionary of Astronomy and Astrophysics
English-French-Persian

Any visible image, however produced. → photograph.

From L. pictura "painting," from pictus, p.p. of pingere "to make pictures, to paint."

Fartur "picture, image; reflexion, inversion" (Dehxodâ, Steingass); maybe from partow, → ray.

A two-dimensional geometric figure. The points of the figure lie entirely in a plane.

→ plane; → figure.

An approximation used in many stellar atmosphere models that depict the atmosphere as being only one-dimensional and bounded at the top and bottom by horizontal plane surfaces normal to the direction of gravity.

→ plane; → parallel; → atmosphere.

The motion of the → ecliptic plane caused by the gravitational influence of the other planets, mainly → Jupiter. The observational effect of planetary precession is similar to that of the → lunisolar precession. But planetary precession causes the → equinoxes to move along the ecliptic in the opposition direction (eastward) from that of luni-solar precession (westward) and at a much slower rate: 0''.12 per year. Same as → precession of ecliptic.

→ planetary; → precession.

A projection or representation of the whole or a part of a sphere on a plane. In particular, a polar projection of the celestial sphere or the Earth on a plane.

→ plani-; → sphere.

The natural frequency at which internal oscillations of a plasma occur. The plasma frequency is proportional to the square root of the electron density. → plasma oscillation.

→ plasma; → frequency.

In the magnetosphere, a region of relatively cool (low energy) and dense plasma that may be considered an outer extension of the ionosphere with which it is coupled. Like the ionosphere, the plasmasphere tends to co-rotate with the Earth.

→ plasma + → sphere.

1) The state or feeling of being pleased.
2) Enjoyment or satisfaction derived from what is to one's liking; gratification; delight.
3) Worldly or frivolous enjoyment (Dictionary.com).

M.E., from O.Fr. plesir, plaisir "enjoyment, delight, desire," from plaisir "to please," from L. placere "to please, give pleasure."

Zusé, from Av. zuš- "to take pleasure;" related to O.Pers. daušta- "friend," Mid.Pers. dôš- "to love, like, choose," dôšišn "pleasure, liking;" Parthian zwš "love;" Mod.Pers. dôst, dust "friend;" cf. Skt. jos- "to like, enjoy;" Gk. geuomai "to taste;" L. gusto "I taste;" gustus "taste, enjoyment."

The equation that expresses the → magnitude  → difference between two objects in terms of the → logarithm of the → flux  → ratio:
I₁/I₂ = 2.5^{(m₂ - m₁)}, or
m₂ - m₁ = 2.5 log(I₁/I₂),
where m is → apparent magnitude, I flux, and log the logarithm to base 10.

Named after Norman Robert Pogson (1829-1891), the English astronomer, who introduced the magnitude scale in 1856; → relation.

In an → isolated system, any initial state will occur again in the course of the → evolution of the system over a sufficiently long but finite → time.

→ Poincaré sphere; → recurrence; → theorem.

A representation that permits an easy visualisation of all different states of → polarization of a vector wave. The equator represents → linear polarization; the north pole corresponds to right-circular and the south pole to left- → circular polarization.

Named after Henri Poincaré (1854-1912), French mathematician and theoretical physicist, and a philosopher of science; → sphere.

The two-dimensional intensity distribution about the image of a point source.

→ point; → spread; → function.

1) A change in the → polarity of Earth's magnetic field in which the north magnetic pole becomes the south magnetic pole and vice versa. Also known as geomagnetic reversal or magnetic reversal. Earth's magnetic field has reversed many times in the past and the time intervals between these changes are known as → polarity epochs.
2) The change in the polarity of the → solar magnetic field with the ending of each → solar activity cycle so that the North magnetic pole becomes the South and vice versa.

→ polarity; → reversal.

→ degree of polarization.

→ polarization; → degree.

1) A small hole such as a space especially in a rock, soil, etc. → porous dust grain, → porosity.
2) A minute orifice in an animal or plant, as in the skin or a leaf.
3) Sun: A small → sunspot that does not have a → penumbra. Pores are up to about 2,500 km across and are lighter than a sunspot's → umbra. They appear and disappear at the surface of the Sun where sunspots are rarely formed, e.g. at low latitudes. Their lifetimes can be as short as 1/2 hour and as long as several days.

From L. porus "a pore," from Gk. poros "a pore," literally "passage, way," from PIE root *per- "to lead, pass over."

Lik, from Gilaki lik "hole," variants luk, luke, liuk, luxa, Tabari luk, li, Sangesari, Semnâni lu, Aftari lo.

Same as → direct correlation.

→ positive; → correlation.

Between two points, the work done in taking the unit test object from one point to the other. Potential is a scalar quantity.

→ potential; → difference.

The space through which electromagnetic radiation passes is filled with electric and magnetic fields at right angles to each other and to the direction of propagation of the radiation. The rate of energy transfer is given by the Poynting vector.

In honor of John Henry Poynting (1852-1914), English physicist; → theorem.

A prefix meaning "before, prior to, in advance of, early, beforehand, in front of."

M.E., from O.Fr. pré-, from L. præ (adverb) "before."

Piš- "before; in front," from Mid.Pers. pêš "before, earlier," O.Pers. paišiya "before; in the presence of."

A precursor of a small, loosely bound → star cluster (→ bound cluster) as well as an → OB association, with masses ranging from about 10 to 1000 → solar masses or more.

→ pre-; → cluster; → core.