An Etymological Dictionary of Astronomy and Astrophysics

1. Something that is borne or carried.
   

2. Computers: To bring (a program or data) into main storage from external or auxiliary storage.
   To place (an input/output medium) into an appropriate device, as by inserting a disk into a disk drive. See also: → download, → upload, → overload.

Etymology (EN): From M.E. lode, originally the same word as lode, from O.E. lāad “way, course, carrying;” cf. O.N. leith “way, route,” O.H.G. leita “procession.”

Etymology (PE): Bâr kardan “to load,” composite verb from bâr “load, charhe, burden,” (Mid.Pers. bâr,
from O.Pers./Av. base bar- “to bear, carry;” Mod.Pers. bordan “to carry;” L. brutus “heavy, dull, stupid, brutish;” Skt. bhara- “burden, load,” bharati “he carries;” Gk. baros “weight;” Mod.Pers. gerân “heavy;” Skt. guru; L. gravis; PIE *gwere- “heavy,” *bher- “carry, give birth”)

• kardan “to do, to make” (Mid.Pers. kardan; O.Pers./Av. kar- “to do, make, build;” Av. kərənaoiti “he makes;” 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 act of a person or thing that loads. See also: → download, → upload.

See also: Verbal noun of → load.

A surface feature on a planet or satellite in the form of a line of cliffs. Lobate scarps are formed when planetary or lunar mantle cools down and contracts inside. The loss of volume squeezes portions of the outer crust together. Eventually, the crust breaks and some of it is pushed up, creating long cliffs that look like wrinkles. Lunar scarps are generally tens of kilometers long and less than 100 m high. They have formed during the last billion years.

See also: Lobate “having the form of a → lobe;” → scarp.

General: A roundish projection that is part of a larger structure.
Radioastronomy: In an antenna pattern, a region of local maximum in the emitted intensity. The strongest lobe is in the pointing direction of a directional antenna and is called the main lobe.
Quasar: One of the two lobe-like structures well apart from the central source, observed
in radio images of some quasars. Same as radio lobe.

Etymology (EN): From M.L. lobus, from L.L. lobus “hull, husk, pod,” from Gk. lobos “lobe of the ear, vegetable pod,” probably related to leberis “husk of fruits;” from PIE base *lep- “to peel, flay.”

Etymology (PE): Lap “lobe,” variants lâp, lâb “piece, big piece, big cut,” lappé “split pea; any of the two parts of a timber split through the length,” maybe
cognate with Gk. lobos, as above. Alternatively, related to Pers. las “loose,” PIE *leu- “to loosen, divide, cut apart” (cf. Gk. lyein “to loosen, untie, slacken,” lysus “a loosening;” L. luere “to loose, release;” → analysis).

The configuration of the response lobes of a radiotelescope.

See also: → lobe; → pattern.

A → radio-loud quasar in which the lobes dominate the whole emission. It has been conjectured that this phenomenon is an → orientation effect. If the → jet is close to the plane of the sky, the lobes will dominate. See also → core-dominated quasar.

See also: → lobe; → dominate; → quasar.

Pertaining to, characteristic of, or restricted to a particular place or particular places.
See also:
→ local arm, → Local Bubble, → Local Group, → local inertial frame, → local interstellar cloud, → local Lorentz invariance, → local maximum, → local meridian, → local oscillator, → local position invariance, → local sidereal time, → local standard of res, → Local Supercluster, → local thermodynamic equilibrium, → local time, → local Universe, → Local Volume, → localization, → localize, → non-local thermodynamic equilibrium.

Etymology (EN): From O.Fr. local, from L.L. localis “pertaining to a place,” from L. locus “place.”

Etymology (PE): Mahali, related to mahal “place, locality,” from Ar.

One of the → spiral arms of the → Milky Way Galaxy which contains our → solar system.
Same as → Orion Arm.

See also: → local; → arm.

A region of low density in the → interstellar medium surrounding the → Solar System. It extends at least 300 → light-years in most directions and encompasses the stars of the immediate → solar neighborhood. The Local Bubble contains a hot, million-degree ionized hydrogen gas that emits in → X-rays. → Neutral hydrogen has a density approximately one tenth of the average for the interstellar medium in the Milky Way. The bubble is thought to be a result of the → shock waves from → supernovae sweeping through the region within the past two to four million years.

See also: → local; → bubble.

A small → galaxy cluster of about 50 galaxies to which our → Milky Way galaxy belongs. The Local Group occupies a volume of space nearly 10 million → light-years
across centered somewhere between the → Andromeda Galaxy (M31) and the Milky Way, which are the dominant galaxies of the group; Andromeda being the principal member. Both of these galaxies exhibit spiral structures, and each is attended by a large family of satellite
→ dwarf galaxies. The Local Group also includes a third spiral galaxy known as → Triangulum (M33), which is bound to Andromeda. The remaining members span a range of → Hubble classification types from dwarf spheroidal to Irr to Sb and Sc and cover a factor of 10 in → metallicity. The total mass of the Local Group is estimated to be about 2 × 10¹² solar masses, although this value is still uncertain to within a factor of about 2. The velocities of the individual galaxies of the Local Group are not particularly high. Therefore no member is believed to be able to escape the group, which is thus considered to be gravitationally → bound. Another remarkable member of the Group is → IC 10.

See also: → local; → group.

A coordinate system or frame of reference defined in the vicinity of the Earth in which Newton’s first law of motion is valid; that is, a non-rotating and non-accelerating reference frame.

See also: → local; → inertial;
→ time.

An → interstellar cloud that surrounds the → heliosphere.

See also: → local; → interstellar; → cloud.

→ Einstein equivalence principle.

See also: → local; → Lorentz; → invariance.

The point x = c in an → interval where the value of the → function  f(y) is larger than the value anywhere else in that interval. In other words, f(c) ≥ f(x) for all x in the interval.

See also: → local; → maximum.

The meridian through any particular place, serving as the reference for local time, in contrast to the Greenwich meridian.

See also: → local; → meridian.

The point x = c in an → interval where the value of the → function  f(y) is smaller than the value anywhere else in that interval. In other words, f(c) ≤ f(x) for all x in the interval.

See also: → local; → minimum.

The oscillator in a heterodyne or superheterodyne radio receiver which produces the radio frequency oscillations with which the received wave is combined.

See also: → local; → oscillator.

→ Einstein equivalence principle.

See also: → local; → position; → invariance.

Local time measured by the apparent motion of the stars. It is the most useful form of sidereal time since it gives the right ascension of a transiting celestial object at a given location.

See also: → local; → sidereal;
→ time.

Same as → Orion Arm.

See also: → local; → → spur.

A frame of reference that turns around the Galactic center at a velocity and a distance which are the mean values for the stars in the solar neighborhood. In this reference system the stars belonging to the solar neighborhood are statistically at rest. The orbital velocity of the Local Standard of Rest around the Galaxy is about 220 km/sec.

See also: → local; → standard;
→ rest.

The supercluster to which the Local Group belongs. It is composed of some 100 clusters of galaxies, with the Virgo cluster of galaxies at its center.

See also: → local; → supercluster.

The assumption that all distribution functions characterizing the material and its interaction with the radiation field at a point in the star are given by → thermodynamic equilibrium relations at local values of the temperature and density.

See also: → local; → thermodynamic; → equilibrium.

Time based upon the local meridian as reference, in contrast to
that of the time zone within which the place is located, or the Greenwich time.

See also: → local; → time.

A not well-defined concept describing a region of radius within ~ 20 → Mpc centered on the → Local Group of galaxies, corresponding to → redshift z ≤ 0.01.
See also the → Local Volume.

See also: → local; → Universe.

A sphere of radius ~ 10 Mpc centered on the → Local Group of galaxies. The Local Volume includes at least 500 known galaxies, many of which congregate in well-known groups like the Local Group, the relatively loose → Sculptor Group, and the more compact Centaurus A group. As of 2010, the latest catalog of LV galaxies was presented by Karachentsev et al. (2004, AJ 127, 2031). About 85% of the LV population are → dwarf galaxies which contribute to about 4% to the local optical luminosity density and roughly to 10-15% to the total H I mass density.

See also: → local; → volume.

The condition of the wave-function of an electron if it is confined to a small region of a large system rather than being extended through the system.

See also: Verbal noun of → localize.

1. To confine, restrict, or attribute to a particular locality.
   
2. To become local, especially to become fixed in one area or part.

See also: From → local + → -ize

1. A device fitted to a gate, door, drawer, lid, etc, to keep it firmly closed and often to prevent access by unauthorized persons.
   

2. To fasten (a door, gate, etc) or (of a door, etc) to become fastened with a lock, bolt, etc, so as to prevent entry or exit (Dictionary.com).

Etymology (EN): M.E., from O.E. loc “fastening, bar;” cognate with M.L.G. lok, O.H.G. loh “dungeon,” Ger. Loch “opening, hole,” O.N. lok “a cover, lid;” akin to O.E. lucan “to shut.”

Etymology (PE): Qofl, loan from Ar.

A region in the sky lying roughly between the → pointer stars
of the → Big Dipper that is almost free from → neutral hydrogen gas in the → Galaxy. It is centered at R.A. 10h 45m, Dec. +57° 20’, has
an area of 15 square degrees, and a → column density of N_{H I} ≤ 5 x 10¹⁸ cm^-2.
The Lockman hole is one of the favorite directions for obtaining a clear and unobstructed view of objects in deep space, far beyond our own Galaxy.

See also: Named after Felix J. Lockman et al., 1986, ApJ 302, 432; → hole.

The aggregate of all possible positions of a moving or generating element, e.g. the locus of points equidistant from a given point is a circle whose center is the given point.

Etymology (EN): From L. locus “place,” from Old L. stlocus, literally “where something is placed,” from PIE base *st(h)el- “to cause to stand, to place.”

Etymology (PE): Mahalgân, from mahal “place, locality” + -gân relation and multiplicity suffix.

A rare type of → achondrite→ meteorite.

See also: Named after Lodhran (Punjab), Pakistan, where the type specimen fell on 1 October 1868.

A low frequency radio telescope network concentrated in the Netherlands with extensions into other European countries. It consists of a core and an extended → array in the Netherlands as well as in surrounding European countries with maximum → baselines of 2 km, 100 km, and 1,000 km respectively. LOFAR will be the largest radio telescope ever built, using a new concept based on a vast array of simple omni-directional antennas. The array will operate at the lowest frequencies that can be observed from Earth, at 30-250 MHz.
About 75% of the construction is finished and LOFAR has already started
its → commissioning period. When entirely finished, it will consist of 45,000 small antennas, distributed within 48 stations in the north east of the Netherlands,
nearby parts of Germany, the UK, France, Sweden, and perhaps later Poland and Spain.
The extensions in the United Kingdom, Germany, and France are completed.
The French extension, located in the Nançay station of Paris Observatory (190 km south of Paris), is fully operational since December 2010. Moreover, a project to extend the low-frequency component of the Nançay station is under study. LOFAR is a forerunner of the future → Square Kilometer Array (SKA) project. See also the LOFAR homepage.

See also: LOFAR, short for → LOw; → Frequency; → ARray.

1. Any of various records, made in rough or finished form, concerning a trip made by a ship or aircraft and dealing with particulars of navigation, weather, engine performance, discipline, and other pertinent details; → logbook.
   

   2. To enter in a log; compile; amass; keep a record of (Dictionary.com).

Etymology (EN): M.E. logge, variant of lugge “pole, limb of tree; piece of wood,” of unknown origin, back formation from logbook, a book used by sailors to record the speed measurements made by means of a chip of a tree log on the end of a reeled log line.

Etymology (PE): 1) Log, loan from E., as above.

2. Logidan, infinitive from log.

Computers: To enter identifying data, as a user name or password, into a database, mobile device, or computer, especially a multi-user computer or a remote or networked system, so as to to access and use it (Dictionary.com).

See also: → log; → in.

Computers: To terminate a session.

See also: → log; → out.

The → exponent of the → power to which it is necessary to raise a fixed number to produce the given number. The fixed number is called the → base. The logarithm of x to the base a, denoted log_a(x), is the unique → real number  y such that a^y = x. In the familiar system of → common logarithms, the base is 10. In the system of → natural logarithms, the base is e = 2.7182818 … (→ number e). For example, the logarithm of 100 (base 10) is 2 because 10² = 100.

See also: Mod.L. logarithmus, coined by Scottish mathematician John Napier (1550-1617), literally “ratio-number,” from Gk. logos “proportion, ratio, word,” → logic + arithmos “number,”
→ arithmetic.

Of or pertaining to a → logarithm.

See also: → logarithm; → -ic.

Same as → reddening coefficient.

See also: → logarithmic; → extinction.

A scale of measurement in which an increase of one unit represents a tenfold increase in the quantity measured (for common logarithms)

Etymology (EN): → logarithmic; → scale.

A book in which details of a trip made by a ship or aircraft are recorded; log (Dictionary.com).

See also: → log; → book.

1. The science that investigates the principles governing correct or reliable inference.
   

2. The system or principles of reasoning applicable to any branch of knowledge or study.
   

3. A particular method of reasoning or argumentation.

Etymology (EN): M.E. logik; O.Fr. logique, from L. (ars) logica, from Gk. logike (techne) “reasoning (art),” from feminine of logikos “pertaining to speaking or reasoning,” from logos “reason, idea, word.”

Etymology (PE): Guyik, from guy- present stem of goftan “to say, speak, relate, tell; to compose a poem,” from Mid.Pers. guftan “to say, tell, utter;” O.Pers. gaub- “to say” + -ik, → -ic.
Cemguyik, from Mid.Pers. cimgôwâgih “logic,” from cim “cause, reason, meaning” (Proto-Iranian *cahmāt “what for;” cf. Skt. kasmāt “why, where from,” kim “what”)

• gôwâgih Mod.Pers. guyi, as above.

A diagram that uses special symbols called logic symbols to represent the detailed functioning of electronic logic circuits. The symbols do not represent the type of electronics used, but only their functions.

See also: → logic; → diagram.

1. According to or agreeing with the principles of logic.
   

2. Reasoning in accordance with the principles of logic, as a person or the mind.
   

3. Of or pertaining to logic (Dictionary.com).

See also: → logic; → -al.

A symbol that can be combined with one or more → sentences in order to form a new sentence. For example “and” (∧), “or” (∨) “not” (¬), “if-then” (→), and “iff” (⇔).

See also: → logical; → connective.

Describing two → compound propositions → if and only if they have the same → truth table.

See also: → logical; → equivalent.

1. The act of logging in to a database, mobile device, or computer, especially a multi-user computer or a remote or networked computer system.
   

   2. A user name and password that allows a person to log in to a computer system, network, mobile device, or user account (Dictionary.com).

See also: → log; → in.

A → probability distribution in which the natural logarithm (logX) of the → random variable (X)
has a → Gaussian distribution.

See also: → logarithm; → normal distribution.

The process by which a computer user logs out.

See also: → log; → out.

An algorithm for detecting and characterizing periodic signals in unevenly-sampled data.

The Lomb-Scargle periodogram has a particularly wide use within the astronomy community. This method allows efficient computation of a Fourier-like → power spectrum estimator from such unevenly-sampled data, resulting in an intuitive means of determining the period of oscillation (see VanderPlas, 2017, astro-ph/1703.09824 and references therein).

See also: Named after Lomb, N. R. 1976, Ap&SS 39, 447 and Scargle, J. D. 1982, ApJ 263, 835; → periodogram.

1. Having considerable linear extent in space. → very-long-baseline interferometry (VLBI).
   

2. Having considerable duration in time. → long-period variable.

Etymology (EN): M.E. longe, O.E. lang, long, akin to O.H.G., Ger. lang “long,” O.N. langr, M.Du. lanc, Goth. laggs “long,” L. longus, → longitude.

Etymology (PE): Derâz “long,” Mid.Pers. drâz “long;” O.Pers. darga- “long;” Av. darəga-, darəγa- “long,” drājištəm “longest;” cf. Skt. dirghá- “lon (in space and time).”

A comet with orbital period of more than 200 years. → short-period comet;
→ periodic comet.

See also: → long; → period; → comet.

A type of → variable star in which variations in brightness occur over long time-scales of months or years. The term generally refers to → Mira variable types.

See also: → long; → period; → variable.

The angular distance on the Earth’s surface, measured east or west from the prime meridian at Greenwich to the meridian passing through a position, expressed in degrees (or hours), minutes, and seconds.

Etymology (EN): L. longitudo “length,” from longus “long,” cognate with Pers. derâz, as below, Gk. dolikhos “elongated;” O.H.G., Ger. lang, O.N. langr, M.Du. lanc, Goth. laggs “long;” PIE base *dlonghos- “long.”

Etymology (PE): Derežnâ, from derež (Kurdi, Laki), variants darg “length; long, tall” (Zâzâ), darγ (Ossetic), derâz “long”

• -nâ noun forming suffix from adjective, as in derâznâ, pah(n)nâ,
  farâxnâ, tangnâ, tiznâ. The first element from Mid.Pers. drâz “long;” O.Pers. darga- “long;” Av. darəga-, darəγa- “long,” drājištəm “longest;” cf. Skt. dirghá- “long (in space and time);” PIE *dlonghos- “long,” as above.

One of the → orbital elements
used to specify the orbit of an object in space. It is the angle from the reference direction, called the origin of longitude, to the direction of the → ascending node, measured in the reference plane.

See also: → longitude; → ascending node.

Of or pertaining to longitude or length. Extending in the direction of the length.

See also: Adj. of → longitude.

1. A → magnetic field whose lines of force (→ line of force) run parallel to the long axis of the → magnet. Longitudinal magnetization of a component can be accomplished using the longitudinal field set up by a → coil or → solenoid. It can also be accomplished using permanent magnets or electromagnets.
   

   2. In → stellar magnetic field observations,
      the magnetic field along the → line of sight.

See also: → longitudinal; → magnetic; → field.

In special relativity theory, the mass of a body when the acceleration is parallel or anti-parallel to velocity: m_l = m₀ / [1 - (v/c)²]^3/2,
where m₀ is the → rest mass, v is the velocity, and c the → velocity of light. → transverse mass.

See also: → longitudinal; → mass.

A wave vibrating along the direction of propagation, such as a → sound wave. → transverse wave.

See also: → longitudinal; → wave.

The → Zeeman effect when the emitting source is viewed in the direction of the magnetic field. In the normal longitudinal effect, each spectral line is split into two components with frequencies ν ± Δν. The line with the frequency ν - Δν shows left-hand → circular polarization and that with frequency
ν + Δν shows right-hand circular polarization. → transverse Zeeman effect.

See also: → longitudinal; → Zeeman effect.

The act or instance of looking.

Etymology (EN): Look, from W.Gmc. *lokjan (cf. O.S. lokon, M.Du. loeken, O.H.G. luogen, Ger. dialectal lugen “to look out”), of unknown origin.

Etymology (PE): Negâh “look,” from Mid.Pers. nikâh “look, glance, observation;” Proto-Iranian *ni-kas- “to look down,” from ni- “down,” → ni- (PIE), + *kas- “to look, appear;” cf. Av. nikā-, nikāta- (in the name of the 15-th nask) “that which is observed,” ākas- “to look;” Mid.Pers. âkâh, Mod.Pers. âgâh “aware, knowing;” Ossetic kast/kaesyn “to look;” Skt. kāś- “to become visible, appear.”

The time that has elapsed since the light was emitted from a distant object (of → redshift z). Because → light moves at a → constant  → speed, it takes a finite time to travel from distant objects. Hence, we “see” distant objects at a point in time in their past. In other words, look-back time is the difference between the age of the Universe now and the age of the Universe at the time the photons were emitted from the object. See also → comoving distance.

Etymology (EN): → look; → back; → time.

Etymology (PE): Zamân, → time; negâh,
→ look; gozašté “past, passed” (from gozaštan “to pass, proceed, go on,” variant gozâštan “to put, to place, let, allow;” Mid.Pers. widardan, widâštan “to pass, to let pass (by);” O.Pers. vitar- “to pass across,” viyatarayam “I put across;” Av. vi-tar- “to pass across,” from vi- “apart, away from” (O.Pers. viy- “apart, away;” Av. vi- “apart, away;” cf. Skt. vi- “apart, asunder, away, out;” L. vitare “to avoid, turn aside”) + O.Pers./Av. tar- “to cross over”).

General: Anything shaped more or less like a loop, i.e. portion of a cord, ribbon, etc., folded or doubled upon itself.
Physics: The part of a vibrating string, column of air or other medium, etc., between two adjacent nodes.
Computers: The reiteration of a set of instructions in a routine or program.

Etymology (EN): Probably of Celtic origin (cf. Gael. lub “bend,” Ir. lubiam), influenced by O.N. hlaup “a leap, run.”

Etymology (PE): Gerdâl, from gerd “round, a circle”
(Mid.Pers. girdag “disk, round,” from gird/girt “round, all around,” Proto-Iranian *gart- “to twist, to wreathe,” cf. Skt krt “to twist threads, spin; to wind; to surround;” kata- “a twist of straw,” Pali kata- “ring, bracelet,” Gk. kartalos “a kind of basket,” kyrtos “curved”) + → -al.

A very bright active prominence in the form of a loop seen in Hα after a rather big flare. Also called “post-flare loops,” they connect the feet where the two-ribbon flares were seen. The lifetime of loop prominences is several hours.

See also: → loop; → prominence.

1. A person who has authority, control, or power over others; a master, chief, or ruler.
   

2. A person who exercises authority from property rights; an owner of land, houses, etc.
   

3. A feudal superior; the proprietor of a manor (Dictionary.com).

Etymology (EN): M.E. lord, loverd, O.E. hlâford, hlâfweard, literally “loaf-keeper,” from hlaf “bread, loaf” + weard “keeper, guardian.”

Etymology (PE): Xâvand, contraction of xodâvand “lord, master, god,” from xodâ “lord, master,” → God, + suffix -vand.

Contraction of the full name of Hendrik Antoon Lorentz (1853-1928), a Dutch physicist, who made important contribution to physics. He won
(with Pieter Zeeman) the Nobel Prize for Physics in 1902 for his theory of electromagnetic radiation, which, confirmed by findings of Zeeman, gave rise to Albert Einstein’s special theory of relativity.

The decrease in the length of a body moving in the direction of its length as measured by an observer situated in that direction. The shortening factor is [1 - (v/c)²]^1/2, where v is the relative velocity and c light speed.

See also: → Lorentz; → contraction.

In → special relativity, an important parameter which appears in several equations, including → time dilation, → length contraction, and → relativistic mass. It is defined as γ = 1 / [1 - (v/c)²]^1/2 = dt/dτ, where v is the velocity as observed in the reference frame where time t is measured, τ is the proper time, and c the → velocity of light. Same as Lorentz γ factor.

See also: → Lorentz; → factor.

The force acting upon a → charged particle as it moves in a → magnetic field. It is expressed by
F = q.v x B, where q is the → electric charge, v is its → velocity, and B the → magnetic induction of the field. This force is perpendicular both to the velocity of the charge and to the magnetic field. The magnitude of the force is F = qvB sinθ, where θ is the angle between the velocity and the magnetic field. This implies that the magnetic force on a stationary charge or a charge moving parallel to the magnetic field is zero. The direction of the force is given by the → right-hand rule.

See also: → Lorentz; → force.

Of a physical law, invariance with respect to a → Lorentz transformation.

See also: → Lorentz; → invariance.

A repeated electromagnetic force on an electrically charged ring particle, nudging the particle in the same direction and at the same point in its orbit. Lorentz resonances are especially important for tiny ring particles whose charge-to-mass ratio is high and whose orbit periods are a simple integer fraction of the rotational period of the planet’s magnetic field (Ellis et al., 2007, Planetary Ring Systems, Springer).

See also: → Lorentz; → resonance.

A set of linear equations that expresses the time and space coordinates of one → reference frame in terms of those of another one when one frame moves at a constant velocity with respect to the other. In general, the Lorentz transformation allows a change of the origin of a coordinate system, a rotation around the origin, a reversal of
spatial or temporal direction, and a uniform movement along a spatial axis. If the system S’(x’,y’,z’,t’) moves at the velocity v with respect to S(x,y,z,t) in the positive direction of the x-axis, the Lorentz transformations will be:

x’ = γ(x - vt), y’ = y, z’ = z, t’ = γ [t - (vx/c²)], where c is the → velocity of light and γ = [1 - (v/c)²]^-1/2. For the special case of velocities much less than c, the Lorentz transformation reduces to → Galilean transformation.

See also: → Lorentz; → transformation.

A spectral profile in which the intensity distribution follows a specific mathematical function (Lorentz or Cauchy probability). Compared to the normal or Gaussian profile, Lorentzian has a pointed peak and more important wings.

See also: → Lorentz; → profile.

The first ever discovered → fast radio burst. It was done during a search of archival data from a 1.4-GHz survey of the → Magellanic Clouds using the multi-beam receiver on the 64-m Parkes Radio Telescope in Australia.

See also: D. R. Lorimer et al., 2007, Science, 318, 777; → burst.

The number of molecules in 1 cm³ of an ideal gas (2.687 x 10¹⁹ per cm³).

Etymology (EN): Joseph Loschmidt (1821-1895), Austrian physicist.

In physics, a measure of the energy, mass, or other physical quantities lost in a system, by conversion or external effects.

Etymology (EN): From O.E. los “loss, destruction,” from P.Gmc. *lausa,
from PIE base *leu- “to loosen, divide, cut apart, untie, separate” (cf. Gk. lyein “to loosen, untie, slacken,” lysus “a loosening;” L. luere “to loose, release, atone for;” Skt. lunati “cuts, cuts off,” lavitram “sickle;” Pers. las “loose,” lâ “slit, cut;” → analysis).

Etymology (PE): Dastraft, literally “gone from hand,” from dast “hand” (Mid.Pers. dast; O.Pers. dasta-; Av. zasta-; cf. Skt. hásta-; Gk. kheir; L. praesto “at hand;” Arm. jern “hand;” Lith. pa-žastis “arm-pit;” PIE *ghes-to-) + raft p.p. of raftan “to go, elapse, glide by, depart” (Mid.Pers. raftan, raw-, Proto-Iranian *rab/f- “to go; to attack”).

High in volume of sound.

Etymology (EN): M.E., O.E. hlud “making noise, sonorous” (cf. M.Du. luut, Du. luid, O.H.G. hlut, Ger. laut “loud”),
from PIE *klutos- (cf. Skt. sruta-, Gk. klytos “heard of, celebrated,” Arm. lu “known.”

Etymology (PE): Boland, → high.

The magnitude of the sensation produced by a sound wave when it reaches the ear. The loudness of a sound depends upon the effective → acoustic pressure and → frequency. The basis of loudness scales is the → Weber-Fechner law.

Etymology (EN): → loud + → -ness.

Etymology (PE): Bolandi, → height; sedâ, → sound.

A device in which electric signals are converted into audible sound.

See also: → loud; → speak; → -er.

1. Below the average or expected degree, amount, or intensity. Having or containing a relatively small amount.
   

2. Situated, placed, or occurring not far above the ground, floor, or base. Relatively little in height.

Etymology (EN): From M.E. lah, from O.N. lagr “low,” from P.Gmc. *lægaz (cf. O.Fris. lech, Du. laag, Ger. läge “low”), literally “that which is lying flat;” related to E. lie (v.).

Etymology (PE): Kam “little, few; deficient, wanting; scarce,” from Mid.Pers. kam “little, small, few,” O.Pers./Av. kamna- “small, few.”
Keh “small, little, slender” (related to kâstan, kâhidan “to decrease, lessen, diminish,” from Mid.Pers. kâhitan, kâstan, kâhênitan “to decrease, diminish, lessen;” Av. kasu- “small, little;” Proto-Iranian *kas- “to be small, diminish, lessen”); kutâh, → small; pâyin, → bottom-up structure.

A redshift characterizing a near-by receding object.

See also: → low; → redshift.

The quality of an instrument that lacks sufficient resolution for a specific observation. This is a relative quality, but
presently a resolution below about 1 arcsecond.

See also: → low; → resolution.

A member of a particularly faint population of galaxies with a central → surface brightness below the brightness of the background sky. The central regions of many of them resemble a → dwarf galaxy, but most of the mass is contained in a large gaseous disk of low density that is observable only with long-exposure optical images or at radio wavelengths. Some are as massive as a large → spiral galaxy, for example Malin 1. The proportion of LSBGs relative to normal galaxies is unknown. They may however represent a significant fraction of mass in the Universe. LSBGs are thought to be primitive systems because they have total masses similar to normal galaxies, but have typically converted less than 10% of their gas into stars. Spiral LSBGs do not obey → Freeman’s law.

See also: → low; → surface; → brightness; → galaxy.

The state of the → tide when at its lowest level.

Etymology (EN): → low; → tide.

Etymology (PE): Owpas, from Persian Gulf dialects, literally “backward water,” from ow, variant of âb, → water, + pas “→ back, behind.”
Jazr, loan from Ar.

Also known as → low tide.

See also: → low; → water.

A neutrino which is mainly produced in → nuclear processes, such as the ones in the → Sun (→ solar neutrino), or in the center of an exploding → supernova. Such neutrinos are, however, more energetic than those making up the → cosmic neutrino background.

See also: → low; → energy; → neutrino.

A spectral line arising from a transition between atomic levels with
an ionization potential below approximately 15 electron-volts.

See also: → low; → ionization; → line.

Same as → LINER.

See also: → low; → ionization;
→ nuclear; → emission;
→ line; → region.

Optical fiber that transmits a greater percentage of input light than does high-loss step-index fiber.

See also: → low; → loss; → fiber.

A galaxy with stellar masses ≤ 10⁹ → solar masses (Dawn K. Erb, 2015, Nature, 9 July).

See also: → low; → mass; → galaxy.

A star whose mass is around that of the Sun. See also: → intermediate-mass star; → high-mass star; → star formation.

See also: → low; → mass; → star.

A member of one of the two main classes of → X-ray binary systems where one of the components is a → neutron star or → black hole and the other component a → low-mass star with a spectral type A or later. LMXBs mainly emit → soft X-rays. The ratio of their optical to X-ray luminosities is less than 0.1. They belong to → old stellar populations with ages 5-15 × 10⁹ years and are found in → globular clusters and in the → bulge of our → Milky Way galaxy; some are also found in the disk.
Hercules X-1 is an example of LMXBs.

See also: → high-mass X-ray binary.

See also: → low; → mass; → X-ray; → binary.

A medium in which chemical elements have abundances smaller than the solar values.

See also: → low; → metallicity; → environment.

Relatively low in position, rank, or order.

See also: Comparative of → low.

Generally and quite loosely, that part of the atmosphere in which most weather phenomena occur (i.e., the → troposphere and lower → stratosphere); hence used in contrast to the common meaning for the → upper atmosphere. In other contexts, the term implies the lower troposphere (Meteorology Glossary, American Meteorological Society).

See also: → lower; → atmosphere.

The instant of culmination when the star passes between the pole and the horizon, having an hour angle of 12h. Lower culmination for non-circumpolar objects occur below the horizon and is thus unobservable. Same as → inferior culmination. See also → upper culmination.

See also: → lower; → culmination.

A → main sequence star whose mass is less than 1.5 Msun. Lower main sequence stars generate their energy chiefly through the → proton-proton chain. The core is surrounded by a → radiative zone above which lies a → convective envelope.

In such stars the → opacity at the surface is high because of the low → surface temperature. Therefore, radiation cannot carry all the radiation because of high opacity. Thus, energy transfer takes place by → convection to the outer layer.

See also: → lower; → main; → sequence.

The part of the Earth’s → mantle extending from about 660 km below the surface to above the → outer core at about 2,900 km.

See also: → lower; → mantle.