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

An irregular galaxy that is much smaller than other irregulars. Dwarf irregulars are generally metal poor and have relatively high fractions of gas. They are thought to be similar to the earliest galaxies that populated the Universe, and are therefore important to understand the overall evolution of galaxies.

→ dwarf; → irregular; → galaxy.

1) Lacking symmetry, even shape, formal arrangement, etc. → irregular galaxy; → irregular variable.
2) Not according to rule, or to the accepted principle, method, course, order, etc.

From O.Fr. irregulier, from M.L. irregularis, from → in- "not" + L. regularis from regula "rule," from PIE *reg- "move in a straight line," hence, "to direct, rule" (cf. Pers. râst "right, straight;" O.Pers. rāsta- "straight, true," rās- "to be right, straight, true;" Av. rāz- "to direct, put in line, set," razan- "order;" Skt. raj- "to direct, stretch," rjuyant- "walking straight;" Gk. orektos "stretched out;" L. regere "to lead straight, guide, rule," p.p. rectus "right, straight;" Ger. recht; E. right).

Bisâmân, from bi- "not, without" + sâmân "order, arrangement, disposition; boundary, limit," Lârestâni sâmon "sign or mark separating one field from another," Gilaki, Tabari šalmân "a straight peace of wood or beam, post;" Mid.Pers. sâmânak, sahmân "limit;" loaned into Arm. sahmân; cf. Skt. sīmān-, sīmā- "boundary, border, limit."

A galaxy with no spiral structure and no symmetric shape. Irregular galaxies are usually filamentary or very clumpy in shape and tend to smaller than others. Two types of irregular galaxies are defined, → Irr I galaxy and → Irr II galaxy.

→ irregular; → galaxy.

A satellite whose orbit around its planet is eccentric, inclined with respect to the equatorial plane, and relatively far from the planet. Strong solar perturbations cause the orbit to precess. → regular satellite.

→ irregular; → satellite.

A type of variable star in which variations in brightness show no regular periodicity. There are two main types, irregular eruptive variables and irregular pulsating variables.

→ irregular; → variable.

1) Evenly or uniformly arranged in space or time; orderly; well-ordered.
Math.: Of a polygon, having all sides and angles equal.
2) Conforming to some accepted rule, discipline, etc.

M.E. reguler, from M.Fr., from O.Fr. reguler, from L.L. regularis "continuing rules for guidance," from L. regula "rule," cognate with Pers. râst, → right.

1) Bâsâmân, from bâ- "with, having" (→ hypo- + sâmân "order, arrangement, disposition; boundary, limit," Lârestâni sâmon "sign or mark separating one field from another," Gilaki, Tabari šalmân "a straight peace of wood or beam, post;" Mid.Pers. sâmânak, sahmân "limit;" loaned into Arm. sahmân; cf. Skt. sīmān-, sīmā- "boundary, border, limit."
2) Razan-mand, from razan, → rule, + -mand a possession suffix.

A function of a complex variable which is single-valued in a domain and which has a finite derivative at every point.

→ regular; → function.

A galaxy which has a uniformly arranged, symmetrical morphology such as a spiral or elliptical galaxy. Opposite of → irregular galaxy.

→ regular; → galaxy.

The reflection of light when the reflecting surface is very smooth and the reflected rays bounce off parallel to each other. Opposite of → diffuse reflection; same as → specular reflection.

→ regular; → reflection.

A satellite that revolves around its planet in an equatorial orbit of low or moderate eccentricity close to the planet. One example of a regular satellite system is the Galilean satellites of Jupiter.

→ regular; → satellite.

A dwarf irregular galaxy, discovered in 1977, that is a member of the Local Group of galaxies. It has a diameter of 1,500 light-years and lies about 3.5 million light-years away. SagDIG contains as much as about 10⁸ solar masses of H I gas and is one of the most metal-poor galaxies. It should not be confused with the → Sagittarius Dwarf Elliptical Galaxy.

→ Sagittarius; → dwarf; → irregular; → galaxy.

A type of giant or supergiant pulsating variable star, with intermediate or late spectra, showing noticeable periodicity in its light changes, accompanied or sometimes interrupted by various irregularities. Periods lie in the range from 20 to more than 2000 days, while the shapes of the light curve may be rather different and variable with each cycle. The amplitudes may be from several hundredths to several magnitudes (usually 1-2 magnitudes in the V filter). Examples are Betelgeuse, Antares, and Rasalgethi. Semiregular variables are classified in several subtypes: SRA, SRB, SRC, and SRD.

→ semi-; → regular; → variable.