An Etymological Dictionary of Astronomy and Astrophysics
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In magnetized disk models, the point where the → poloidal velocity equals the → Alfven speed. Within this point, the magnetic energy density dominates, and the gas is forced to flow along the field lines. Well beyond this point, the kinetic energy acquired by the flowing gas prevails and the field is forced to follow the flow.

→ Alfven wave; → point.

Meteo.: The point on the → celestial sphere that lies directly opposite the Sun from the → observer, observer, that is, on the line from the Sun through the observer. The antisolar point is the center of the rainbow, and can be easily found on a sunny day: it it located at the shadow of one's head; it is 180° away from the Sun. If the Sun is in the sky, the antisolar point is below the horizon. If the Sun has set, the antisolar point is above the horizon.

→ anti-; → solar; → point.

A → neutral point located at about 20° above the → antisolar point.

Named for François Arago (1786-1853), French physicist; → point

One of several points on the sky where the degree of → linear polarization is zero in skylight. See also → neutral point; → Arago point, → Brewster point.

→ Babinet compensator; → point.

The point or moment in the evolution of a → dynamical system that occurs if a parameter passes through a critical point. At this point the system branches into any number of qualitatively new types of behavior.

→ bifurcation; → point.

The temperature at which a liquid changes to a gas (vapor) at normal atmospheric pressure. In other words, the temperature at which the vapor pressure of a liquid is equal to the external pressure.

M.E. boillen; O.Fr. boillir, from L. bullire "to bubble, seethe," from bulla "a bubble, knob;" → point.

Noqté, → point; juš "boiling," present stem of jušidan "to boil;" Khotanese jis- "to boil;" Av. yaēšiiant- "boiling;" cf. Skt. yas- "to boil, become hot," yasyati "boils, seethes;" Gk. zein "to bubble, boil, cook;" O.H.G. jesan "to ferment, foam;" Ger. Gischt "foam, froth," gären "to ferment;" O.E. gist; E. yeast.

A → neutral point located 15 to 20° directly below the Sun.

→ Brewster's law; → point

One of the four points where the → meridian and the → prime vertical intersect the → horizon. See also: → cardinal direction.

→ cardinal; → point.

Two points positioned along the principal axis of a mirror or lens so that light coming from one focuses onto the other.

→ conjugate; → point.

A symbol (usually a point or dot) used to separate the integer part from the fractional part of a → decimal number.

→ decimal; → point.

Jodâgar, → separator.
Momayez, from Ar. mumaiyiz "distinguisher, discerner, separator."

The temperature to which a given air parcel must be cooled at constant pressure and constant water vapor content in order for saturation to occur.

→ dew; → point.

One of the two points of intersection of the ecliptic and the celestial equator. Same as equinox.

→ equinoctial; → point.

One of the two points on the celestial sphere where the ecliptic and the celestial equator crossed one another at → vernal equinox several thousands years ago.

→ first; → point; → Aries.

One of the two points on the celestial sphere where the ecliptic and the celestial equator crossed one another at → autumnal equinox several thousands years ago. Because of → precession, this equinoctial point no longer lies in Libra but in neighboring Virgo.

Same as → focus.

→ focal; → point.

1) The temperature at which a liquid of specified composition changes into a solid under a specified pressure.
2) The temperature at which the liquid and solid phases of a substance of specified composition coexist in equilibrium.

→ freezing; → point.

The temperature at which a mixture of air-saturated pure water and pure ice may exist in equilibrium at a pressure of one standard atmosphere.

→ ice; → point.

One of the points constituting an extended image formed in an → optical system.

→ image; → point.

A point on a → curve at which the → tangent changes direction, from rotating in one sense to rotating in the opposite sense.

→ inflection; → point.

One of the five → Lagrangian points, denoted L1, which lies between the two bodies on the line passing through their center of mass. In a → close binary star system mass transfer occurs through this point.

→ inner; → Lagrangian points.