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

A metallic chemical element; symbol Na (L. natrium]. Atomic number 11; atomic weight 22.98977; melting point 97.81°C; boiling point 892.9°C; specific gravity 0.971 at 20°C. It was discovered in 1807 by the English chemist Humphry Davy from electrolysis of caustic soda (NaOH).

Sodium, from soda (NaOH).

The → sodium tail of the Moon as it appears in the sky opposite the Sun. The SMS undergoes changes in shape and brightness. It is brighter when the → new moon occurs at → perigee, when the new moon is north of the → ecliptic, and approximately five hours after the new moon.

→ sodium; → Moon; → spot.

1) A kind of → cometary tail appearing in some → comets, such as → Hale-Bopp. Sodium tails arise from the very strong → fluorescence of their sodium atom → D lines in the visible. They are rapidly accelerated to high velocities by the Sun, forming a very straight tail distinct from the → ion tail. The release mechanism of sodium from comets is still a matter of debate. Also called → neutral tail.
2) → sodium tail of the Moon.
3) A comet-like tail of Mercury similar to that of the Moon, but much longer, stretching up to 3.5 million km.

→ sodium; → tail.

A comet-like tail of the Moon comprised of → sodium (Na) atoms and invisible to the naked eye. The lunar surface is constantly bombarded by the → solar wind, → photons, and → meteoroids, which can liberate Na atoms from the → regolith. These atoms are subsequently accelerated by solar → radiation pressure to form a long comet-like tail opposite the Sun. Near → new moon, this diffuse cloud of Na atoms encounters the Earth's gravity and is "pinched" into a beam of enhanced density. This beam appears as the ~3° diameter Sodium Moon Spot (SMS) seen in the sky opposite the Sun. The spot is about five times the diameter of the → full moon, and is 50 times fainter than can be seen with the unaided eye. The spot is reflected light from millions of Na atoms that two days earlier were on the surface of the Moon. This spot is visible to sensitive cameras equipped with filters tuned to the orange light emitted by Na atoms near 589.3 nm (Baumgardner et al., 2021 Journal of Geophysical Research: Planets DOI: 10.1029/2020je006671).

→ sodium; → tail; → Moon.

General: Delicate in texture, grain, or fiber.
Not bright or glaring.
Physics: Of a beam of particles or electromagnetic radiation, having relatively low energy, as opposed to → hard. → soft X-rays

M.E. softe "yielding, gentle, mild;" O.E. softe "gentle, easy;" cf. O.S. safti, O.H.G. semfti, Ger. sanft, M.Du. sachte, Du. zacht.

Narm "soft; smooth; mild," from Mid.Pers. narm "soft; humble."

In → stellar dynamics studies of → three-body encounters, a → binary system whose → binding energy is smaller than the typical → kinetic energy of the relative motion of an incoming third body. See also → hard binary.

→ soft; → binary.

A member of a small class of objects which emit intense bursts of → gamma rays and → X-rays (> 100 keV) at irregular intervals. The bursts last for some 100 milli-seconds. It is conjectured that they are → magnetars. See also → starquake.

→ soft; → gamma rays; → repeater.

Same as → soft gamma repeater (SGR).

→ soft; → gamma ray; → repeater.

Iron that has a low carbon content, in contrast to → steel. Because it is easily magnetized and demagnetized, it is used to make the cores of → solenoids and other electrical equipment.

→ soft; → iron.

The back, muscular (not bony) part of the roof of the → mouth in front of the → pharynx.

→ soft; → palate.

An → X-ray binary system that has a long period of → quiescence interrupted by → outbursts of low-energy → soft X-rays. Alternatively known as X-ray novae, the majority (~ 75%) of SXTs contain a → black hole and a low-mass → main sequence  → companion star in orbit around one another. It is thought that SXTs arise in a similar manner to → dwarf novae, through instabilities in the → accretion disk around the → compact object (→ disk instability model).

→ soft; → X-ray; → transient..

X-ray photons with energies between about 0.1 to 10 keV. → hard X-rays.

→ soft; → X-rays.

A general term used to describe a collection of computer programs, procedures, and documentation that perform some tasks on a computer system. → hardware.

→ soft + ware, from M.E., from O.E. waru, from P.Gmc. *waro (cf. Swed. vara, Dan. vare, M.Du. were, Du. waar, Ger. Ware "goods").

Narm, → soft + afzâr "instrument, means, tool," from Mid.Pers. afzâr, abzâr, awzâr "instrument, means," Proto-Iranian *abi-cāra- or *upa-cāra-, from cāra-, cf. Av. cārā- "instrument, device, means" (Mid.Pers. câr, cârag "means, remedy;" loaned into Arm. aucar, aucan "instrument, remedy;" Mod.Pers. câré "remedy, cure, help"), from kar- "to do, make, build;" kərənaoiti "he makes" (Pers. kardan, kard- "to do, to make"); cf. Skt. kr- "to do, to make," krnoti "he makes, he does," karoti "he makes, he does," karma "act, deed;" PIE base k^wer- "to do, to make").

The overall structure of a software system consisting of mutually dependent components that create a logical whole.

→ software; → architecture.

All loose, unconsolidated earth and organic materials above bedrock that support plant growth.

M.E. soile, O.Fr. soil "piece of ground, place," from L. solium "seat," meaning confused with that of L. solum "soil, ground."

Xâk, from Mid.Pers. xâk "earth, dust," ultimately from Proto-Ir. *āika-, from *āi- "earth, soil," cf. Av. āi- "earth, soil," Gk. aia "earth, land," + suffix -ka. The initial x- is a prothesis, as in xâya "egg" (Gershevitch 1962).

The solar day on Mars, which has a mean period of 24 hours 39 minutes 35.244 seconds (based on SI units), about 2.7% longer than Earth's solar day. The Martian sidereal day, as measured with respect to the fixed stars, is 24h 37m 22.663s, as compared with 23h 56m 04.0905s for Earth.

Sol, from L. sol "sun," cognate with Pers. hur, → Sun.

Of or pertaining to the Sun.

Adjective from L. sol; → Sun.

→ solar photospheric abundance, → solar system abundance.

→ solar; → abundance.

The general term for all forms of short-lived phenomena on the Sun, including → solar flares, → sunspots, → prominences, etc., indicating that the Sun is an active star.

→ solar; → activity.

Same as the → solar cycle.

→ solar activity; → cycle.