An Etymological Dictionary of Astronomy and Astrophysics

A general purpose software package for the reduction and analysis of astronomical data. It is aimed specifically at the reduction of imaging and spectroscopy data obtained using → CCD detector systems. IRAF is developed by the National Optical Astronomy Observatories (NOAO).

See also: Short for Image Reduction and Analysis Facility.

A general purpose software package for the reduction and analysis of astronomical data. It is aimed specifically at the reduction of imaging and spectroscopy data obtained using → CCD detector systems. IRAF is developed by the National Optical Astronomy Observatories (NOAO).

See also: Short for Image Reduction and Analysis Facility.

The most accurate solar calendar in use, which is based on
two successive passages of the Sun through the true vernal equinox.
The year length, defined by an ingenious intercalation system devised by the mathematician Omar Khayyâm (A.D. 1048-1131), is 365.2424.. solar days,
in perfect agreement with the → vernal-equinox year of 365.24236 solar days (epoch +2000). This interval should not be confounded with the → tropical year of 365.2422 solar days. The most remarkable
feature of the calendar is Nowruz, the spring festival, which has its profound roots in the Zoroastrian worldview. Same as → Persian calendar. Click here for more details.

Etymology (EN): Iranian, of or pertaining to Iran “(land of) the Aryans,” as below;
→ calendar.

Etymology (PE): Gâhšomâr, → calendar; Irâni adj. of Irân, from Mid.Pers. Êrân “(land of) the Aryans,” pluriel of êr “noble, hero,” êrîh “nobility, good conduct;” Parthian Mid.Pers. aryân; O.Pers. ariya- “Aryan;” Av. airya- “Aryan;” cf. Skt. ārya- “noble, honorable, respectable.”

The most accurate solar calendar in use, which is based on
two successive passages of the Sun through the true vernal equinox.
The year length, defined by an ingenious intercalation system devised by the mathematician Omar Khayyâm (A.D. 1048-1131), is 365.2424.. solar days,
in perfect agreement with the → vernal-equinox year of 365.24236 solar days (epoch +2000). This interval should not be confounded with the → tropical year of 365.2422 solar days. The most remarkable
feature of the calendar is Nowruz, the spring festival, which has its profound roots in the Zoroastrian worldview. Same as → Persian calendar. Click here for more details.

Etymology (EN): Iranian, of or pertaining to Iran “(land of) the Aryans,” as below;
→ calendar.

Etymology (PE): Gâhšomâr, → calendar; Irâni adj. of Irân, from Mid.Pers. Êrân “(land of) the Aryans,” pluriel of êr “noble, hero,” êrîh “nobility, good conduct;” Parthian Mid.Pers. aryân; O.Pers. ariya- “Aryan;” Av. airya- “Aryan;” cf. Skt. ārya- “noble, honorable, respectable.”

The condition or state of being → iridescent; exhibition of colors like those of the → rainbow.

Etymology (EN): From L. iris (genitive iridis) “rainbow,” + → -escence.

The condition or state of being → iridescent; exhibition of colors like those of the → rainbow.

Etymology (EN): From L. iris (genitive iridis) “rainbow,” + → -escence.

Producing a display of lustrous, rainbow-like colors.

See also: → iridescence

Producing a display of lustrous, rainbow-like colors.

See also: → iridescence

A metallic chemical element; symbol Ir. Atomic number 77; atomic weight 192.22; melting point about 2,410°C; boiling point about 4,130°C; specific gravity 22.55 at 20°C. Iridium is a very hard, usually brittle, extremely corrosion-resistant silver-white metal with a face-centered cubic crystalline structure. The unusually high concentration of iridium found in the thin clay layer that marks the boundary between the Cretaceous and Tertiary rocks is attributed to an asteroid impact with Earth 65 million years ago.

See also: Iridium coined 1804 by its discoverer, E. chemist Smithson Tennant (1761-1815) from Gk. → iris “rainbow;” so called for the varying color of its compounds.

A metallic chemical element; symbol Ir. Atomic number 77; atomic weight 192.22; melting point about 2,410°C; boiling point about 4,130°C; specific gravity 22.55 at 20°C. Iridium is a very hard, usually brittle, extremely corrosion-resistant silver-white metal with a face-centered cubic crystalline structure. The unusually high concentration of iridium found in the thin clay layer that marks the boundary between the Cretaceous and Tertiary rocks is attributed to an asteroid impact with Earth 65 million years ago.

See also: Iridium coined 1804 by its discoverer, E. chemist Smithson Tennant (1761-1815) from Gk. → iris “rainbow;” so called for the varying color of its compounds.

1a) The circular diaphragm forming the colored portion of the eye and perforated by the pupil in its center. → pupil.

1b) A diaphragm forming an adjustable opening over a lens in an optical instrument.

2. Asteroid 7, discovered in 1847 by E. astronomer John Russell Hind (1823-1895).
   

3. Botany: A plant having showy flowers, typically of purple, yellow, or white, and long thin leaves.

Etymology (EN): Iris, M.E., from L. irid-, iris “colored part of the eye, rainbow, iris plant, a precious stone,” from Gk. iris, iridos “rainbow, iris plant, iris of the eye,” initially “a messenger of the gods, regarded as the goddess of the rainbow.” The eye portion was so called for being the colored part.

Etymology (PE): Titak, from Kermâni, Tâleši, variants Lori tiya, Dehxodâ dictionary tuk, probably from didan “to see,” Mid.Pers. ditan “to see, regard, catch sight of, contemplate, experience;” O.Pers. dī- “to see;” Av. dā(y)- “to see,” didāti “sees;” cf. Skt. dhī- “to perceive, think, ponder; thought, reflection, meditation,” dādhye; Gk. dedorka “have seen.”
Zanbaq, from Pers. zanba “white rose.”

1a) The circular diaphragm forming the colored portion of the eye and perforated by the pupil in its center. → pupil.

1b) A diaphragm forming an adjustable opening over a lens in an optical instrument.

2. Asteroid 7, discovered in 1847 by E. astronomer John Russell Hind (1823-1895).
   

3. Botany: A plant having showy flowers, typically of purple, yellow, or white, and long thin leaves.

Etymology (EN): Iris, M.E., from L. irid-, iris “colored part of the eye, rainbow, iris plant, a precious stone,” from Gk. iris, iridos “rainbow, iris plant, iris of the eye,” initially “a messenger of the gods, regarded as the goddess of the rainbow.” The eye portion was so called for being the colored part.

Etymology (PE): Titak, from Kermâni, Tâleši, variants Lori tiya, Dehxodâ dictionary tuk, probably from didan “to see,” Mid.Pers. ditan “to see, regard, catch sight of, contemplate, experience;” O.Pers. dī- “to see;” Av. dā(y)- “to see,” didāti “sees;” cf. Skt. dhī- “to perceive, think, ponder; thought, reflection, meditation,” dādhye; Gk. dedorka “have seen.”
Zanbaq, from Pers. zanba “white rose.”

A mechanical device, consisting of thin overlapping plates, designed to smoothly vary the effective diameter of a lens, thereby controlling the amount of light allowed through.

See also: → iris; → diaphragm.

A mechanical device, consisting of thin overlapping plates, designed to smoothly vary the effective diameter of a lens, thereby controlling the amount of light allowed through.

See also: → iris; → diaphragm.

Same as → NGC 7023.

See also: → iris; → nebula.

Same as → NGC 7023.

See also: → iris; → nebula.

A metallic → chemical element occurring abundantly in combined forms and used alloyed in a wide range of important tools and structural materials; symbol Fe. → Atomic number 26; → atomic weight 55.845; → melting point about 1,535°C; → boiling point about 2,750°C; → specific gravity 7.87 at 20°C; → valence +2, +3, +4, or +6.

Iron is of critical importance to life, i.e. plants, humans, and animals. It occurs in hemoglobin, a molecule that carries → oxygen from the lungs to the tissues and then transports → carbon dioxide (CO₂) back from the tissues to the lungs.

Iron has the highest nuclear → binding energy of all elements, and is therefore the most stable element. It is synthesized in → massive stars, and its occurrence ends the process of → thermonuclear reaction in stars. The resulting energy crisis leads to the destruction of the star through a → supernova explosion. It has several → radioactive isotopes with half-lives from 6 min (⁶¹Fe) to about 3 x 10⁵ years (⁶⁰Fe).

Etymology (EN): Iron, from O.E. isærn, from P.Gmc. *isarnan (cf. O.S. isarn, O.N. isarn, M.Du. iser, O.H.G. isarn, Ger. Eisen) “holy metal” or “strong metal,” probably an early borrowing of Celt. *isarnon (cf. O.Ir. iarn, Welsh haiarn), from PIE *is-(e)ro- “powerful, holy,” from PIE *eis “strong” (cf. Skt. isirah “vigorous, strong,” Gk. ieros “strong”).

The chemical symbol Fe, from L. ferrum “iron.”

Etymology (PE): Âhan, Kurd. âsan, Mid.Pers. âhan; Av. aiianhaēna- “made of metal,” from aiiah- “metal;” cf. Skt. áyas- “iron, metal;”  L. aes “brass;” Goth. aiz “bronze;” O.H.G. ēr “ore” (Ger. Erz “oar”); O.E. ora “ore, unworked metal,” ar “brass, copper, bronze.”

A metallic → chemical element occurring abundantly in combined forms and used alloyed in a wide range of important tools and structural materials; symbol Fe. → Atomic number 26; → atomic weight 55.845; → melting point about 1,535°C; → boiling point about 2,750°C; → specific gravity 7.87 at 20°C; → valence +2, +3, +4, or +6.

Iron is of critical importance to life, i.e. plants, humans, and animals. It occurs in hemoglobin, a molecule that carries → oxygen from the lungs to the tissues and then transports → carbon dioxide (CO₂) back from the tissues to the lungs.

Iron has the highest nuclear → binding energy of all elements, and is therefore the most stable element. It is synthesized in → massive stars, and its occurrence ends the process of → thermonuclear reaction in stars. The resulting energy crisis leads to the destruction of the star through a → supernova explosion. It has several → radioactive isotopes with half-lives from 6 min (⁶¹Fe) to about 3 x 10⁵ years (⁶⁰Fe).

Etymology (EN): Iron, from O.E. isærn, from P.Gmc. *isarnan (cf. O.S. isarn, O.N. isarn, M.Du. iser, O.H.G. isarn, Ger. Eisen) “holy metal” or “strong metal,” probably an early borrowing of Celt. *isarnon (cf. O.Ir. iarn, Welsh haiarn), from PIE *is-(e)ro- “powerful, holy,” from PIE *eis “strong” (cf. Skt. isirah “vigorous, strong,” Gk. ieros “strong”).

The chemical symbol Fe, from L. ferrum “iron.”

Etymology (PE): Âhan, Kurd. âsan, Mid.Pers. âhan; Av. aiianhaēna- “made of metal,” from aiiah- “metal;” cf. Skt. áyas- “iron, metal;”  L. aes “brass;” Goth. aiz “bronze;” O.H.G. ēr “ore” (Ger. Erz “oar”); O.E. ora “ore, unworked metal,” ar “brass, copper, bronze.”

The period generally occurring after the → Bronze Age, marked by the widespread use of iron. Its date and context vary depending on the country or geographical region. The Indo-European Hittites are the first people to work iron, in the Asia Minor, from about 1500 BC.

See also: → iron; → age.

The period generally occurring after the → Bronze Age, marked by the widespread use of iron. Its date and context vary depending on the country or geographical region. The Indo-European Hittites are the first people to work iron, in the Asia Minor, from about 1500 BC.

See also: → iron; → age.

A → convective zone close to the surface of → hot stars caused by a peak in the → opacity due to iron recombination. A physical connection may exist between → microturbulence in hot star atmospheres and a subsurface FeCZ. The strength of the FeCZ is predicted to increase with
→ metallicity and → luminosity, but decrease with → effective temperature.
The FeCZ in hot stars might also produce localized surface magnetic fields. The consequence of the FeCZ might be strongest in → Wolf-Rayet stars. These stars are so hot that the → iron opacity peak, and therefore FeCZ, can be directly at the stellar surface or, better said, at the → sonic point of the wind flow. This may relate to the very strong → clumping found observationally in Wolf-Rayet winds, and may be required for an understanding of the very high → mass loss rates of Wolf-Rayet stars (See Cantiello et al. 2009, A&A 499, 279).

See also: → iron; → convection; → zone.

A → convective zone close to the surface of → hot stars caused by a peak in the → opacity due to iron recombination. A physical connection may exist between → microturbulence in hot star atmospheres and a subsurface FeCZ. The strength of the FeCZ is predicted to increase with
→ metallicity and → luminosity, but decrease with → effective temperature.
The FeCZ in hot stars might also produce localized surface magnetic fields. The consequence of the FeCZ might be strongest in → Wolf-Rayet stars. These stars are so hot that the → iron opacity peak, and therefore FeCZ, can be directly at the stellar surface or, better said, at the → sonic point of the wind flow. This may relate to the very strong → clumping found observationally in Wolf-Rayet winds, and may be required for an understanding of the very high → mass loss rates of Wolf-Rayet stars (See Cantiello et al. 2009, A&A 499, 279).

See also: → iron; → convection; → zone.

1. Electromagnetism: A bar of → soft iron that passes through a coil and serves to increase the → inductance of the coil.
   

2. The innermost part of some planets, such as Mercury, Venus, and Earth, which have a molten iron-rich core.
   

3. The end point in the evolution of stars with a mass above ~ 10 → solar masses. Such a star evolves in several stages over millions of years during which various → thermonuclear reactions take place in the star core. Each stage results in a core composed of heavier elements. The process ends when → silicon burning produces a core of iron-nickel. Since iron has the maximum → binding energy per → nucleon, the → nuclear fusion cannot proceed further. The iron core shrinks and heats up. It is maintained against → gravitational collapse by → electron degeneracy pressure, but it continues to grow as Si burning adds more iron. When the core reaches its → Chandrasekhar limit, it becomes unstable and undergoes the → core collapse.

See also: → iron; → core.

1. Electromagnetism: A bar of → soft iron that passes through a coil and serves to increase the → inductance of the coil.
   

2. The innermost part of some planets, such as Mercury, Venus, and Earth, which have a molten iron-rich core.
   

3. The end point in the evolution of stars with a mass above ~ 10 → solar masses. Such a star evolves in several stages over millions of years during which various → thermonuclear reactions take place in the star core. Each stage results in a core composed of heavier elements. The process ends when → silicon burning produces a core of iron-nickel. Since iron has the maximum → binding energy per → nucleon, the → nuclear fusion cannot proceed further. The iron core shrinks and heats up. It is maintained against → gravitational collapse by → electron degeneracy pressure, but it continues to grow as Si burning adds more iron. When the core reaches its → Chandrasekhar limit, it becomes unstable and undergoes the → core collapse.

See also: → iron; → core.

A meteorite which is composed mainly of iron mixed with smaller amounts of → nickel. Iron meteorites make up about 4.4% of all meteorites. See also → stony meteorite, → stony-iron meteorite.

See also: → iron; → meteorite.

A meteorite which is composed mainly of iron mixed with smaller amounts of → nickel. Iron meteorites make up about 4.4% of all meteorites. See also → stony meteorite, → stony-iron meteorite.

See also: → iron; → meteorite.

A bump appearing in the plot of stellar → opacity versus temperature. The ionization of the heaviest → chemical elements, especially → iron, which is the most abundant heavy metal, produces a large number of weak spectral → absorption lines. These lines dominate the stellar opacity in the temperature range 10⁵-10⁶ K and furnish two local opacity peaks: a large peak around 2 × 10⁵ K and a smaller one around 1.5 × 10⁶ K (Rogers & Iglesias, 1992, ApJS 79, 507;
Iglesias et al. 1992, ApJ, 397, 717).

See also: → iron; → opacity; → peak.

A bump appearing in the plot of stellar → opacity versus temperature. The ionization of the heaviest → chemical elements, especially → iron, which is the most abundant heavy metal, produces a large number of weak spectral → absorption lines. These lines dominate the stellar opacity in the temperature range 10⁵-10⁶ K and furnish two local opacity peaks: a large peak around 2 × 10⁵ K and a smaller one around 1.5 × 10⁶ K (Rogers & Iglesias, 1992, ApJS 79, 507;
Iglesias et al. 1992, ApJ, 397, 717).

See also: → iron; → opacity; → peak.

A maximum on the element-abundance curve in the vicinity of the iron → atomic number 26. The relative higher abundance of the → iron peak elements results from their being the end products of → nucleosynthesis in the interiors of → massive stars.

See also: → iron; → peak.

A maximum on the element-abundance curve in the vicinity of the iron → atomic number 26. The relative higher abundance of the → iron peak elements results from their being the end products of → nucleosynthesis in the interiors of → massive stars.

See also: → iron; → peak.

A member of a group of elements with → atomic masses A about 40 to 60 that are synthesized by the → silicon burning process and appear in the → iron peak. They are mainly: → titanium (Ti), → chromium (Cr), → manganese (Mn), → iron (Fe), → cobalt (Co), and → nickel (Ni).

See also: → iron; → peak; → element.

A member of a group of elements with → atomic masses A about 40 to 60 that are synthesized by the → silicon burning process and appear in the → iron peak. They are mainly: → titanium (Ti), → chromium (Cr), → manganese (Mn), → iron (Fe), → cobalt (Co), and → nickel (Ni).

See also: → iron; → peak; → element.

1. Using words to convey a meaning that is the opposite of its literal meaning; containing or exemplifying irony: an ironic novel; an ironic remark.
   

2. Of, pertaining to, or tending to use irony or mockery; ironical (Dictionary.com).
   

See also: → irony; → -ic.

1. Using words to convey a meaning that is the opposite of its literal meaning; containing or exemplifying irony: an ironic novel; an ironic remark.
   

2. Of, pertaining to, or tending to use irony or mockery; ironical (Dictionary.com).
   

See also: → irony; → -ic.

1. The humorous or mildly sarcastic use of words to imply the opposite of what they normally mean. → ironic.
   

2. An instance of this, used to draw attention to some incongruity or irrationality (Dictionary.com).

Etymology (EN): From L. ironia, from Gk. eironeia “dissimulation, assumed ignorance,” from eiron “dissembler,” perhaps related to eirein “to speak.”

Etymology (PE): Govâžé, ultimately from Proto-Ir. *ui-vac-, from *ui- prefix denoting “apart, away, out,” cf. Av. vi-, O.Pers. viy-, Skt. vi- (Mod.Pers., e.g., gozidan, → select, gozaštan “to cross,” → passage) + *uac- “to say, speak,” → word; also govâžidan “to make irony of, to say ironically.”

1. The humorous or mildly sarcastic use of words to imply the opposite of what they normally mean. → ironic.
   

2. An instance of this, used to draw attention to some incongruity or irrationality (Dictionary.com).

Etymology (EN): From L. ironia, from Gk. eironeia “dissimulation, assumed ignorance,” from eiron “dissembler,” perhaps related to eirein “to speak.”

Etymology (PE): Govâžé, ultimately from Proto-Ir. *ui-vac-, from *ui- prefix denoting “apart, away, out,” cf. Av. vi-, O.Pers. viy-, Skt. vi- (Mod.Pers., e.g., gozidan, → select, gozaštan “to cross,” → passage) + *uac- “to say, speak,” → word; also govâžidan “to make irony of, to say ironically.”

An → irregular galaxy that shows a hint of a spiral arm or bar, and can be placed at the far end of spirals in the → Hubble sequence.

See also: → irregular; → galaxy.

An → irregular galaxy that shows a hint of a spiral arm or bar, and can be placed at the far end of spirals in the → Hubble sequence.

See also: → irregular; → galaxy.

An amorphous, → irregular galaxy that does not appear to show any structure that can place it into the → Hubble sequence.

See also: → irregular; → galaxy.

An amorphous, → irregular galaxy that does not appear to show any structure that can place it into the → Hubble sequence.

See also: → irregular; → galaxy.

The → energy at all → wavelengths that is incident on unit area of surface in unit time. It is measured in Watts per square meter.

Etymology (EN): Irradiance, from ir- variant of → in- (by assimilation) before r + radi(ant), → radiation, + -ance a suffix used to form nouns either from adjectives in -ant or from verbs.

Etymology (PE): Tâbešdâri, from tâbeš, → radiation, + dâri, verbal noun from dâštan “to have, hold,” → property.

The → energy at all → wavelengths that is incident on unit area of surface in unit time. It is measured in Watts per square meter.

Etymology (EN): Irradiance, from ir- variant of → in- (by assimilation) before r + radi(ant), → radiation, + -ance a suffix used to form nouns either from adjectives in -ant or from verbs.

Etymology (PE): Tâbešdâri, from tâbeš, → radiation, + dâri, verbal noun from dâštan “to have, hold,” → property.

To expose something to → radiation.

Etymology (EN): → irradiance.

Etymology (PE): Tâbeš, → radiation, dâdan “to give,” → irradiation.

To expose something to → radiation.

Etymology (EN): → irradiance.

Etymology (PE): Tâbeš, → radiation, dâdan “to give,” → irradiation.

1. Exposure to any kind of radiation or atomic particles.
   
2. An optical effect that makes a bright object appear larger than it really is when viewed against a darker background.

Etymology (EN): Irradiation, from ir- variant of → in- (by assimilation) before r + → radiation.

Etymology (PE): 1) Tâbešdehi, tâbešgiri;, from tâbeš→ radiation + giri verbal noun of gereftan “to take, seize” (Mid.Pers. griftan, Av./O.Pers. grab- “to take, seize,” cf.
Skt. grah-, grabh- “to seize, take,” graha “seizing, holding, perceiving,” M.L.G. grabben “to grab,” from P.Gmc. *grab, E. grab “to take or grasp suddenly;” PIE base *ghrebh- “to seize”); dahi verbal noun of dâdan “to give,” Mid.Pers. dâdan “to give” (O.Pers./Av. dā- “to give, grant, yield,” dadāiti “he gives;” Skt. dadáti “he gives;” Gk. tithenai “to place, put, set,” didomi “I give;”
L. dare “to give, offer,” facere “to do, to make;” Rus. delat’ “to do;” O.H.G. tuon, Ger. tun, O.E. don “to do;” PIE base *dhe- “to put, to do”).
2) Nurgostard, from nur, → light, + gostard past stem of gostardan “to expand; to spread; to diffuse” (Mid.Pers. wistardan “to extend; to spread;” Proto-Iranian *ui.star-; Av. vi- “apart, away from, out” (O.Pers. viy- “apart, away;” cf. Skt. vi- “apart, asunder, away, out;” L. vitare “to avoid, turn aside”) + Av. star- “to spread,” starati “spreads;” cf. Skt. star- “to spread out, extend, strew,”
strnati “spreads;” Gk. stornumi “I spread out,” strotos “spread, laid out;” L. sternere “to spread;” Ger.
Strahlung “radiation,” from strahlen “to radiate,” from Strahl “ray;” from M.H.G. strāle; from O.H.G. strāla “arrow,” stripe; PIE base *ster- “to spread”).

1. Exposure to any kind of radiation or atomic particles.
   
2. An optical effect that makes a bright object appear larger than it really is when viewed against a darker background.

Etymology (EN): Irradiation, from ir- variant of → in- (by assimilation) before r + → radiation.

Etymology (PE): 1) Tâbešdehi, tâbešgiri;, from tâbeš→ radiation + giri verbal noun of gereftan “to take, seize” (Mid.Pers. griftan, Av./O.Pers. grab- “to take, seize,” cf.
Skt. grah-, grabh- “to seize, take,” graha “seizing, holding, perceiving,” M.L.G. grabben “to grab,” from P.Gmc. *grab, E. grab “to take or grasp suddenly;” PIE base *ghrebh- “to seize”); dahi verbal noun of dâdan “to give,” Mid.Pers. dâdan “to give” (O.Pers./Av. dā- “to give, grant, yield,” dadāiti “he gives;” Skt. dadáti “he gives;” Gk. tithenai “to place, put, set,” didomi “I give;”
L. dare “to give, offer,” facere “to do, to make;” Rus. delat’ “to do;” O.H.G. tuon, Ger. tun, O.E. don “to do;” PIE base *dhe- “to put, to do”).
2) Nurgostard, from nur, → light, + gostard past stem of gostardan “to expand; to spread; to diffuse” (Mid.Pers. wistardan “to extend; to spread;” Proto-Iranian *ui.star-; Av. vi- “apart, away from, out” (O.Pers. viy- “apart, away;” cf. Skt. vi- “apart, asunder, away, out;” L. vitare “to avoid, turn aside”) + Av. star- “to spread,” starati “spreads;” cf. Skt. star- “to spread out, extend, strew,”
strnati “spreads;” Gk. stornumi “I spread out,” strotos “spread, laid out;” L. sternere “to spread;” Ger.
Strahlung “radiation,” from strahlen “to radiate,” from Strahl “ray;” from M.H.G. strāle; from O.H.G. strāla “arrow,” stripe; PIE base *ster- “to spread”).

A → real number which cannot be exactly expressed as a ratio ^a/_b of two integers. Irrational numbers have decimal expansions that neither terminate nor become periodic. Every → transcendental number is irrational. The most famous irrational number is √ 2.

See also: From ir- a prefix meaning “not,” a variant of → in-,

• → rational; → number.

A → real number which cannot be exactly expressed as a ratio ^a/_b of two integers. Irrational numbers have decimal expansions that neither terminate nor become periodic. Every → transcendental number is irrational. The most famous irrational number is √ 2.

See also: From ir- a prefix meaning “not,” a variant of → in-,

• → rational; → number.

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.

Etymology (EN): 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).

Etymology (PE): 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.”

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.

Etymology (EN): 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).

Etymology (PE): 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.

See also: → irregular; → galaxy.

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.

See also: → 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.

See also: → irregular; → satellite.

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.

See also: → 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.

See also: → irregular; → variable.

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.

See also: → irregular; → variable.

Not relevant to or connected with what is considered.

See also: → in- “not;” → relevant.

Not relevant to or connected with what is considered.

See also: → in- “not;” → relevant.

Not capable of returning to an original condition.
→ irreversible process.

See also: Irreversible, from ir- “not,” variant of → in- + → reversible.

Not capable of returning to an original condition.
→ irreversible process.

See also: Irreversible, from ir- “not,” variant of → in- + → reversible.

A physical process in which the combined → entropy of the → system and the → environment increases. During an irreversible process the system is not in equilibrium at all instances of time. Most of the processes in nature are irreversible. → reversible process.

See also: → irreversible; → process.

A physical process in which the combined → entropy of the → system and the → environment increases. During an irreversible process the system is not in equilibrium at all instances of time. Most of the processes in nature are irreversible. → reversible process.

See also: → irreversible; → process.