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

A configuration in which the constituting parts are arranged concentrically around the center of a sphere.

→ spherical; → symmetry.

A triangle drawn on the → surface of a → sphere. A spherical triangle, like a plane triangle, may be right, obtuse, acute, equilateral, isosceles, or scalene. The sum of the angles of a spherical triangle is greater than 180° (π) and less than 540° (3π). See also → spherical excess.

→ spherical; → triangle.

A body that is shaped like a sphere but is not perfectly round, especially an ellipsoid that is generated by revolving an ellipse around one of its axes.

→ sphere; → -oid.

Shaped like a → spheroid.

→ spheroid; → -al.

Any of many vitrified droplets of rock formed by the solidification of molten meteoritic material that flows off a meteorite during its passage through the Earth's atmosphere. Sizes range typically from 10 to 200 microns.

"Small sphere," from → sphere + diminutive suffix → -ule.

Guyel "small globe," from guy "ball, sphere" (variants golulé, gullé, goruk, gulu, gudé; cf. Skt. guda- "ball, mouthful, lump, tumour," Pali gula- "ball," Gk. gloutos "rump," L. glomus "ball," globus "globe," Ger. Kugel, E. clot; PIE *gel- "to make into a ball") + -el diminutive suffix, → -ule.

The brightest star in the constellation → Virgo, and the 15th brightest star in the night sky. Also known as HD 116658. It is 260 → light-years distant from Earth. A → blue giant, it is a variable → eclipsing binary, with a period of 4.014 days. Both components are → B-type stars, the → primary being a → Beta Cephei variable near to core hydrogen exhaustion (→ spectral type B1 III-IV) and the → secondary a → main sequence star (B2 V). See, e.g., R.S. Schnerr et al., 2010, arXiv:1008.4260.

From L. spica "ear of grain," related to spina "thorn," corresponding to Gk. stakhys "grapes."

Sonbolé, from sonbol "an ear of corn; a hyacinth," from Ar. sumbul.

Any of numerous vertical → spikes of → gas visible in the → monochromatic light of certain strong → spectral lines beyond the → Sun's limb. Spicules are short-lived phenomena, corresponding to rising → jets of gas that move upward at about 30km/sec up to 10,000 km and last only about 10 minutes.

From L. spiculum "spearhead, arrowhead, bee stinger," from spica "ear of grain" + -ulum, → -ule.

Sixak, from six "spur, spit; thorn; any pointed thing."

One of, usually three or four, diagonal supports that hold the → secondary mirror in a → reflecting telescope. Also called support vane.

M.E. spithre, O.E. M.E. spithra, akin to spinnan "to spin;" cf. M.L.G., M.Du., M.H.G., Ger. spinne, Du. spin "spider;" → vane.

Parré, → vane; târtan "spider," literally "weaver," composite word of with two cognate elements, the first one târ "thread, warp, string," related to tur "net, fishing net, snare," tâl "thread" (Borujerdi dialect), tân "thread, warp of a web," from the second element tan-, tanidan "to spin, twist, weave;" Mid.Pers. tanitan; Av. tan- to stretch, extend;" cf. Skt. tan- to stretch, extend;" tanoti "stretches," tántra- "warp; essence, main point;" Gk. teinein "to stretch, pull tight;" L. tendere "to stretch;" Lith. tiñklas "net, fishing net, snare," Latv. tikls "net;" PIE base *ten- "to stretch."

1) A long, pointed → metal  → bar.
2) Physics: A → transient variation in → voltage or → current in an → electric circuit.

M.E. spik(e) from O.N. spikr "nail;" akin to M.L.G. spiker "nail."

Sixak, from six "spur, spit; thorn; any pointed thing," + -ak a suffix of similarity and nuance.

1) Mechanics: The rotation of a body about an axis through the body. To cause to turn around rapidly, as on an axis. To revolve or rotate rapidly,
2) Quantum mechanics: See → spin quantum number; → spin angular momentum.

M.E. spinnen; O.E. spinnan "to draw out and twist fibers into thread" (cf. O.N., O.Fris. spinna, Dan. spinde, Du. spinnen, O.H.G. spinnan, Ger. spinnen); cognate with Pers. tan-, tanidan "to spin, twist, weave" (Mid.Pers. tanitan; Av. tan- to stretch, extend;" cf. Skt. tan- to stretch, extend;" tanoti "stretches," tántra- "warp; essence, main point;" Gk. teinein "to stretch, pull tight;" L. tendere "to stretch;" Lith. tiñklas "net, fishing net, snare," Latv. tikls "net;" PIE base *ten- "to stretch").

Espin, loan from E., as above.

An intrinsic quantum mechanical characteristic of a particle that has no classical counterpart but may loosely be likened to the classical → angular momentum of a particle arising from rotation about its own axis. The magnitude of spin angular momentum is given by the expression S = ħ √ s(s + 1), where s is the → spin quantum number. As an example, the spin of an electron is s = 1/2; this means that its spin angular momentum is (ħ /2) √ 3 or 0.91 x 10^-34 J.s. In addition, the projection of an angular momentum onto some defined axis is also quantized, with a z-component S_z = m_sħ. The only values of m_s (magnetic quantum number) are ± 1/2. See also → Stern-Gerlach experiment.

→ spin; → angular; → momentum.

The magnetic moment associated with the → spin angular momentum of a charged particle. The direction of the magnetic moment is opposite to the direction of the angular momentum. The magnitude of the magnetic moment is given by: μ = -g(q / 2m)J, where q is the charge, m is the mass, and J the angular momentum. The parameter g is a characteristic of the state of the atom. It would be 1 for a pure orbital moment, or 2 for a spin moment, or some other number in between for a complicated system like an atom. The quantity in the parenthesis for the electron is the → Bohr magneton. The electron spin magnetic moment is important in the → spin-orbit interaction which splits atomic energy levels and gives rise to → fine structure in the spectra of atoms. It is also a factor in the interaction of atom with external fields, → Zeeman effect.

→ spin; → magnetic moment.

An integer or half-integer on which the magnitude of a particle's → spin angular momentum depends. It is expressed in units of → Planck's constant divided by 2π. Called also spin, denoted s. The spin of a particle can only have a value that is zero or a multiple of 1/2. Particles with half-integer spins, 1/2, 3/2, 5/2, ..., are → fermions. Particles with integer spin (0, 1, 2, ...) are called → bosons.

→ spin; → quantum; → number.

The → excitation temperature of the → hyperfine structure levels of the → neutral hydrogen→ 21-centimeter line.

→ spin; → temperature.

A phenomenon in which the rotation period of a pulsar steadily decreases with the pulsar age. The cause of the spin-down is magnetic torque due to the strong fields threading out from the pulsar. The magnetic energy is being converted to high-energy particles and radiation from the nebula. Observed spin-down rates range from about 10^-5 seconds/year for the youngest pulsars to about 10^-12 seconds/year for recycled pulsars. The Crab pulsar is slowing down at a rate of about 10^-5 seconds/year. Knowing the rotation period and the lengthening rate of a pulsar leads to its age.

→ spin; down, M.E.; O.E. ofdune "downward," from dune "from the hill."

Kond-carxi, from kond "slow; dull" + carx→ rotate + -i noun suffix.

Quantum mechanics: The scattering of a particle that reverses the spin direction.

→ spin; flip, from flip-flap; → scattering.

Parâkaneš, → scattering; bâ "with;" vâruni, noun from vârun, → inverse; espin, → spin.

1) Astro.: A relationship between the orbital period of one body around another and its rotational period on its axis. The relationship results from tidal forces between the two bodies. For example, the rotation period of the Moon equals its revolution period around the Earth.
2) Quantum mechanics: The interaction between a particle's → spin angular momentum and its → orbital angular momentum.

→ spin; → orbit; → coupling.

1) A rounded rod, usually of wood, tapering toward each end, used in hand-spinning to twist into thread the fibers drawn from the mass on the distaff, and on which the thread is wound as it is spun (Dictionary.com).
2) → Spindle Galaxy.

M.E. spindel, O.E. spin(e)l, from spinnan, → spin.

Duk "spindle," variants dêk, dik, ultimately from Proto-Ir. *dau- "to run;" cf. Pers. dow-, davidan "to run" (Cheung 2007).

Same as → NGC 5866.

→ spindle; → galaxy.

1) In 3D → magnetic reconnection models of solar plasma, a field line crossing the → fan at the → magnetic null point. See also → fan (Lau & Finn. 1990, ApJ 350, 672; Parnell et al. 1996, Physics of Plasmas 3, 759).
2) A very narrow line of light extending back from the coma into the tail of some → comets.

M.E., from O.Fr. espine, from L. spina "backbone," originally "thorn, prickle," cf. L. spica "ear of corn," O.N. spikr "nail;" from PIE *spei- "sharp point."

Xâr "spine, thorn," related to xal-, xalidan "to prick, to pierce," xâridan "to scratch, itch;" Av. x^vara- "wound, sore."