An Etymological Dictionary of Astronomy and Astrophysics
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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.

From O.Fr. local, from L.L. localis "pertaining to a place," from L. locus "place."

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.

→ 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.

→ 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.

→ 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.

→ local; → inertial; → time.

An → interstellar cloud that surrounds the → heliosphere.

→ local; → interstellar; → cloud.

→ Einstein equivalence principle.

→ 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.

→ local; → maximum.

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

→ 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.

→ local; → minimum.

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

→ local; → oscillator.

→ Einstein equivalence principle.

→ 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.

→ local; → sidereal; → time.

Same as → Orion Arm.

→ 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.

→ 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.

→ 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.

→ 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.

→ 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.

→ 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.

→ local; → volume.