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

The size range from approximately 1 → nanometer (nm) to 100 nm.

→ nano-; → scale.

The time required for a star to exhaust its hydrogen (H) supply in → nuclear fusion. The nuclear time scale is given by the relation t = E/L, where E is the total nuclear energy that can be generated by a star and L is the stellar → luminosity. Assuming that the end point of fusion is → iron (Fe), the → atomic mass difference between H and Fe is Δm = 0.008 m_H. Therefore, the maximum amount of energy a star with a hydrogen mass M can release is Δ M = 0.008 Mc². The nuclear time scale is then: t = 0.008 c²M/L. However, stars use up only a fraction of their hydrogen supply, because only the inner part of the star is hot enough for fusion. For example, the Sun will spend only about 10% of its hydrogen supply before evolving into a → red giant. In other words, the solar life time on the → main sequence is about 10¹⁰ years.

→ nuclear; → time; → scale.

A technical scale that categorizes the → impact hazard of a → near-Earth object (NEO). It compares the threat of a given NEO to the so-called background threat of all NEOs of the same size or larger. In this way, the probability of the → impact itself as well as the time until the predicted impact are considered. The scale is → logarithmic and continuous. A Palermo scale of -2 indicates that the predicted event is only 1% as likely as a random background event between now and the time of predicted impact. A value of 0 indicates that the risk is the same as the risk from the background threats. A value of +2 indicates an event that is 100 times more likely than the background hazard. The Palermo scale is defined in the paper "Quantifying the risk posed by potential Earth impacts" by Chesley et al. (2002), Icarus 159n 423. See also → Torino scale.

Named after Palermo, in recognition of the Palermo Observatory, where in 1801 the first and largest asteroid (→ Ceres) was discovered by the Italian astronomer Giuseppe Piazzi (1746-1826); → scale.

1) A general term for anything roughly the size of the → Planck length.
2) Similarly, an energy on the order of the → Planck energy.

→ Planck; → scale.

The scale factor for converting linear measure on a photographic plate to angular measurement on the sky.

→ plate; → scale.

A basic ingredient of the → mixing length theory that scales with the → mixing length. It is defined by the relation: H_P = -dr/dln P = -Pdr/dP , where r is the height and P the pressure. See also → scale height.

→ pressure; → scale; → height.

A temperature scale in which the degree intervals are the same size as in the → Fahrenheit scale, but 0 is set at absolute zero, -459.69 °F. Therefore, 1 degree Rankine is equal to exactly 5/9 → kelvin. It was formerly used by engineers in English-speaking countries, but is now obsolete. See also → Celsius scale, → Kelvin scale, → Reaumur scale.

Named for the British physicist and engineer William John Rankine (1820-1872); → scale.

A temperature scale in which the → freezing point and the → boiling point of → water are set to 0 and 80 degrees respectively. See also → Celsius scale, → Fahrenheit scale, → Kelvin scale, → Rankine scale.

Named after René Antoine Ferchault de Réaumur (1683-1757), who first proposed it in 1730; → scale.

A temperature scale in which the → freezing point and the → boiling point of → water are set to 0 and 80 degrees respectively. See also → Celsius scale, → Fahrenheit scale, → Kelvin scale, → Rankine scale.

Named after René Antoine Ferchault de Réaumur (1683-1757), who first proposed it in 1730; → scale.

1a) A succession or progression of steps or degrees.
1b) A standard of measurement or estimation; point of reference by which to gauge or rate.
2) To reduce or increase according to a common proportion (often followed by down or up).

M.E., from L. scalae "ladder, stairs."

Marpel, literally "measuring stick, measuring step," on the model of Ger. Maßstab from Mass "measure" + Stab "stick, bar, pole, baton." The first element from Mod./Mid.Pers. mar "measure, count," from Av. mar- "to count, remember;" Skt. smr, smarati "to remember, he remembers;" L. memor, memoria; Gk. mermera "care," martyr "witness." The second element pel "stick, a bit of wood;" pel can also be interpreted as the contraction of pellé "staircase, ladder."

In computer science, to reduce the processing power of the same node/system by reducing its resources (CPU, RAM, etc.). This type of → vertical scaling is opposite to → scale up. See also → scale in, → scale out.

→ scale; → down.

Math.: A number which scales, or multiplies, some quantity. In the equation y = Cx, C is the scale factor for x. C is also the coefficient of x, and may be called the constant of proportionality of y to x.
Geometry: The ratio of any two corresponding lengths in two similar geometric figures. The ratio of areas of two similar figures is the square of the scale factor.

→ scale; → factor.

The height within which some parameter, such as pressure or density, decreases by a factor of e. For example, an atmospheric scale height of 100 km means that the value at 100 km is 1/e the value at the surface.

→ scale; → height.

In computer science, to reduce the number of nodes (servers), as opposed to → scale out. Scale-in is a type of → horizontal scaling. See also → scale up, → scale down.

→ scale; → in.

In computer science, to upgrade a system by increasing the number of nodes. For example, instead of going from a CPU of X and memory of Y to a CPU with 4X and 4Y memory, use 4 machines with CPU of X and memory of Y. This is a type of → horizontal scaling. See also → scale in, → scale up, → scale down.

→ scale; → out.

In computer science, to increase the processing power of the same node/system by increasing its resources (CPU, RAM, etc.). This is a type of → vertical scaling opposite to → scale down. For example, instead of a machine with a CPU running at speed of X and having Y gigabytes of memory, use a machine with a CPU running at speed of 4X and a memory of 4Y gigabytes. See also → scale in, → scale out.

→ scale; → up.

A triangle no two sides of which are equal.

From L.L. scalenus, from Gk. skalenos "uneven, unequal, rough," from skallein "chop, hoe," related to skolios "crooked," from PIE base *(s)qel- "crooked, curved, bent;" → triangle.

Sebar, → triangle; nâjur-pahlu "dissimilar sides," from nâjur "dissimilar, ill-matched" + pahlu "side, flank" (Mid.Pers. pahlug "side, rib," Av. pərəsu- "rib," Ossetic fars "side, flank," cf. Skt. párśu- "rib," Lith. piršys (pl.) "horse breast").

An electronic circuit devised to give a single pulse after a prescribed number of input pulses have been received.

Agent noun from → scale.

The time necessary for a star to form. It depends inversely on the stellar mass.

→ star formation; → time scale.

A measure of duration of a specific process, such as → crossing time, → dynamical time scale, → evolutionary time scale, → Kelvin-Helmholtz time scale, → nuclear time scale, → photon escape time, → relaxation time, → star formation time scale.

→ time; → scale.