An Etymological Dictionary of Astronomy and Astrophysics

Suffix forming adjectives with meanings “capable of, susceptible of, worthy of, tending to.”

Etymology (EN): M.E., from O.Fr., from L. -abilis, -ibilis, from -a- and -i- + -bilis.

Etymology (PE): The capability suffix -i is added to the infinitive form.
-pazir “receiving, accepting, admitting, having,” from paziroftan “to receive, accept, admit,” Mid.Pers. padiriftan, padir- “to receive, accept,” from Proto-Iranian *pati- + *grab- “to grab, seize, take,” Av./O.Pers. grab- “to take, seize;” cp. Skt. grah-, grabh- “to seize, take,” graha “seizing, holding, perceiving,” M.L.G. grabben “to grab,” from P.Gmc. *grab (E. grab); PIE *ghrebh- “to seize.”

A prefix with several meanings: “characterized by,” “of the nature of,”
“belonging to or connected with a division of animals characterized by or of the nature of,” “belonging to or connected with a family of plants of the nature of.”

Etymology (EN): From L. -aceus.

Etymology (PE): -âsâ a suffix denoting “resemblance; nature; relation,” from Mid.Pers. suffix -ihâ forming adverbs.

1. Adjective suffix denoting “of, relating to, or characterized by;” e.g. astronomical, material, equal, final, general, directional, fictional, etc. Variant
   → -ar.
   

2. Noun suffix, used with verbs (refusal, rehearsal, etc.) or nouns (canal, etc.).

Etymology (EN): 1) M.E., from O.Fr., from L. -alis
2) M.E. -aille, from O.Fr., from L. -alia, from neuter pl. of -alis.

Etymology (PE): 1) -i, contraction of -ik, → -ic; -var Mid.Pers. -uwar, -war, from O.Pers. -bara, from bar- “to bear, carry,” variant -ur; -mand from Mid.Pers. -omand, O.Pers./Av. -mant, cf. Skt. -mant.

2. In Persian, -âl, a suffix of attributes and similarity, is used to form adjectives that often become nouns. Sometimes it occurs as -al or -el and may be confounded with -ul and -ulé, → -ule. Its link with L. -alis is not established. Some examples:
   dombâl “rear part; continuation; tail,” from domb “tail” + -âl,
   cangâl “fork; claws,” from cang “claw; hook” + -âl,
   pušâl “tinder, rubbish,” from puc, puk “hollow” + -âl,
   ravâl “trend,” from row present stem of raftan “to go” + -âl,
   xoškâl “dried twigs and leaves of a green tree,” from xošk “dry” + -âl,
   tofâl “remains of anything squeezed,” from tof “saliva” + -âl,
   kupâl “club,” from kup-, kub(idan) “to beat, strike, pound”
   • -âl,
     gowdâl “hole, pit, low place,” from gowd “deep”
   • -âl,
     tâval “blister,” from tâv-, tâb-, tâbidan “to become warm, burn,” + -al.
     kandâl “pit (Qâeni), watercourse, canal (Kordi),” from kand stem of kandan “to dig, pluck, extract” + -âl,
     mərdâl (Tâleši Xošabar) “dead,” from mərd “to die”

• -âl,
  capâl “left-handed,” from cap “left” + -âl,
  gaštal (Laki) “wanderer, vagabond,” from gaštan “to turn, return, change, look about” + -al,
  kašal (Torbat Heydariye-yi) “elongated,” from kašidan “to draw, extend”
• -al,
  gerdel (Hamadâni, Lori, Qomi) “round, loop,” from gerd “round” + -el,
  peškel “orbicular dung of sheep,” from pešk “dung” + -el.

Suffix used to form nouns either from adjectives or from verbs; it
expresses 1) state or condition (brilliance, absorptance); 2) action (e.g. continuance).

Etymology (EN): M.E., from O.Fr., from L. -antia.

Etymology (PE): -Egi, -igi, -âi, -âyi, -eš Pers. noun suffixes denoting state, condition.

Same as → -ent.

A suffix of adjectives, meaning “of, relating to, or resembling,” as in polar “of or relating to”: molecular,
“being”: spectacular.

Etymology (EN): M.E., from O.Fr. -er, from L. -aris, variant of -alis, → -al.

An adjective and noun suffix denoting thing or person belonging to or connected with.

Etymology (EN): From L. -arius, -aria, -arium “connected with, pertaining to; the man engaged in.”

Etymology (PE): -i, Mid.Pers. -ig, -ik, → -ics.

1. A suffix used in chemical terminology, in particular to indicate a salt of an acid ending in -ic and not beginning with → hydro-, such as silicate, nitrate, sulfate.
   

2. Verbal suffix denoting “to act upon” (in a specific way), “to cause to become.”

See also: 1) From M.E. -aten, from L. -atus p.p. ending of 1st conjugable verbs.

2. Very likely from N.L. expressions as plumbum acetatum salt produced by the action of acetic acid on lead.

A suffix meaning “killer; act of killing.” → genocide.

Etymology (EN): M.E., from L. -cida “cutter, killer,” -cidium “act of killing,” from combining form -cidere, from caedere “to strike down, kill.”

Etymology (PE): -koši, from koštan “to kill,” Mid.Pers. kuštan “to kill, to stuggle;” related to košti “fighting, wrestling;” Av. kuš- “to fight, to struggle” (Cheung 2007).

A suffix indicating a slope, as in → barocline, → thermocline, → tachocline.

Etymology (EN): Back formation from incline, → inclination.

Etymology (PE): Šib, → slope.

A combining form occurring in loanwords from Greek with the meaning “rule, government, governing body.” → theocracy.

Etymology (EN): From Fr. -cratie, from M.L. -cratia, from Gk. -kratia “power, might; rule; authority,” from kratos “strength,” from PIE *kre-tes- “power, strength,” suffixed form of root *kar-/*ker- “→ hard.” “hard.”

Etymology (PE): From sâlâr “leader, chieftain, commander;” Mid.Pers. sâlâr “leader, master;”
variant of sardâr “commander, chief, general,” from sar “chief, → head,” + dâr “having, possessor,” from dâštan “to have, to possess,” Mid.Pers. dâštan; O.Pers./Av. root dar- “to hold, keep back, maintain, keep in mind;” Skt. dhr-, dharma- “law;”
Gk. thronos “elevated seat, throne;” L. firmus “firm, stable;” Lith. daryti “to make;” PIE *dher- “to hold, support.”

A noun suffix equivalent to → -ance.

See also: → -ance.

A suffix denoting quality or state.

See also: From L. -entia.

A suffix with the sense “causing or performing an action or existing in a certain condition.” Same as → -ant.

See also: From Fr. -ent and directly from L. -entem (nominative -ens), pr.p. suffix of verbs in -ere/-ire.

An adjective forming suffix with the meanings “ccomposed of, resembling, having the nature of.”

See also: → -ous.

A suffix serving as the regular English formative of agent nouns, being attached to verbs of any origin.

Etymology (EN): M.E. -er(e), corresponding to L. → -or,
O.E. -ere; cf. Ger. -er, Sw. -are, Dan. -ere.

Etymology (PE): → -or.

A suffix denoting “action, process, state, or condition,” and corresponding to adjectives ending in -escent. → luminescence.

Etymology (EN): From L. -escentia, from escens, from esse “to be,” → existence, + -ia

Etymology (PE): -esti, noun from -est, variant of ast, hast “is, → exists,” cognate with L. -escence, as above.

A suffix of adjectives often corresponding to verbs in -esce and nouns in -escence. → luminescent.

Etymology (EN): From -escentia, from escens, from esse “to be,” → existence, + -ia.

Etymology (PE): → -escence.

Suffix meaning “to make, cause to be.”

Etymology (EN): From Fr. -fier, from L. -ficare, from facere “to make, do;” cognate with Pers. dâdan “to give;” → fact.

Etymology (PE): Suffix -idan forming infinitives; kardan “to do, to make,” → -ize; sâxtan “to build, make, fashion,” → perfect; ârdan contraction of âvardan “to bring; to cause, produce” (Mid.Pers. âwurtan, âvaritan; Av. ābar- “to bring; to possess,” from prefix ā- + Av./O.Pers. bar- “to bear, carry,” bareθre “to bear (infinitive),” bareθri “a female that bears (children), a mother;” Mod.Pers. bordan “to carry;” Skt. bharati “he carries;” Gk. pherein; L. fero “to carry”).

A combining form (also -gene) used in the formation of compound words, meaning:

1. “one that generates:” → hydrogen,
   → halogen, andogen, and so on. 2) “one that is generated, produced:” exogen, cultigen, phosgene.

See also: From Fr. -gène “producing,” Gk. -genes “produced, born,” → generate;

A combining form of genesis.

See also: From L. genesis, from Gk. genesis “origin, generation,” from gignesthai “to be born,” related to genos “race, birth, descent,” cognate with Pers. zâdan “to bring forth, give birth,” → generate.

A combining form meaning “angled, angular,” used in the formation of compound words. → heptagon, → hexagon, → polygon.

Etymology (EN): From Gk. gonia “angle,” related to gony “knee;” L. genu “knee;” Mod.Pers. zânu “knee;” Av. žnav-, žnu- “knee;” Skt. janu-; PIE base *g(e)neu-.

Etymology (PE): From bar “side; breadth; breast,” variant var (Mid.Pers. var “breast;” Av. vouru “wide, broad, extended” (vourucašāni- “looking far”), related to varah- “breast;” cf. Skt. urú- “wide, broad,” úras- “breast;” Gk. eurus “wide, broad;” PIE base uer-, ueru-s“wide, broad”); -guš “corner, angle,” Mid.Pers. gošak “corner.”

A combining form meaning “something drawn, written” (diagram, spectrogram, oscillogram).

Etymology (EN): From Gk. -gramma, combining form of gramma “something written or drawn,” → graph.

Etymology (PE): -Negâšt, from negâšt “drawn, written;” p.p. of negâštan, negârdan “to paint, write,” → graph.

A suffix meaning “drawn, written,” specialized in meaning to indicate the instrument rather than the written product of the instrument.

Etymology (EN): A suffix, from Gk. -graphos “(something) drawn or written, one who draws or writes,” from graphein “to draw, write.”

Etymology (PE): A suffix from the stem of negârdan, negâštan “to paint, write,” → graph.

An adjective relating to → -graph.

See also: → -graph + → -ic.

A combining form denoting a process or form of drawing, writing, representing, recording, describing, etc., or an art or science concerned with such a process. Examples: geography; orthography; → photography; → radiography; → selenography;
→ tomography.

See also: → graph.

A combining form meaning “face” used in the names of geometrical solid figures having the form or number of faces specified by the initial element.

Etymology (EN): N.L., from Gk -edron, from hedra “seat, base, chair, face of a geometric solid,” from PIE root *sed- “to → sit.”

Etymology (PE): Dimé, from dim, → face.

A suffix forming a noun meaning “healing, medical practice.” Same as → -iatry.

Etymology (EN): From -iatr(y), from Gk. iateria “heling,” iatros “heal”, + → -ics.

Etymology (PE): Pezeški, → medicine, darmâni, from darmân, → remedy.

Same as → -iatrics.

A suffix forming adjectives from nouns and bearing several senses; adjective suffix of nouns ending in → -ics.

See also: → -ics.

A suffix of nouns that denotes science, knowledge, principles, characteristic actions or activities, such as → physics, → statistics, → ballistics, politics, ethics. See also → -logy.

Etymology (EN): Suffix -ics, from -ic + plural suffix -s, from O.Fr. -ique, from L. -icus, Gk. -ikos; cf. O.E. -ig, from P.Gmc. *-iga, Ger. -ig.

Etymology (PE): Mod.Pers. -ik, from Mid.Pers. -ik or -ig, possibly from
the Av. noun and adjective forming suffix -ika, -ka, -aka (as in ainika- “face,” maršdika- “mercy,” pairikā- “fairy,” kasvika- “trifling,” kutaka- “small,” ahmāka- “ours”). In Mid.Pers. it had an extensive use for creating adjectives of relation. Some examples:
cihrik, cihrig “natural,” from cihr (Mod.Pers. cehr);
gohrik, gohrig “natural, essential,” from gohr (Mod.Pers. gowhar);
gumânik, gumânig “doubtful,” from gumân (Mod.Pers. gomân);
kunišnik “doable, related to action,” from konišn (Mod.Pers. koneš);
mânik, mânig “household belonging, household member,” from mân (Mod.Pers. mân);
manik “mine, related to me,” from man (Mod.Pers. man);
narik “related to male,” from nar (Mod.Pers. nar);
xvartik, xwarišnig “edible,” from xvart, xwarišn (Mod.Pers. xord, xoreš);
gâsânik, gâhânig “related to the Gathas (the oldest songs of the Avesta, which are attributed to Zarathushtra himself),” from gâsân (Mod.Pers. gâhân);
dâtik, dâdig “legal, concerned with the law,” from dât (Mod.Pers. dâd).

Although it has changed into -i in Mod.Pers. (like O.E. -ig into E. -y, as in juicy, dreamy), it is extant in a number of adjectives: târik “dark;” nazdik “near;” bârik “narrow;” zandik (Arabicized zandiq) “heretic;” Monjik (Termezi), pen name of an 11th century Persian poet, from monj “honeybee,” referring to his poems being as sweet as honey.

The suffix is active in the Tabari dialect, as in larzenik “subject to fear, full of fear, timorous, fearful,” ramendik “timid, fugitive,” xordinik “very small,” bermendik, bərmənik “person who cries easily, highly sensitive person,” from bərmən “cry,” and also appears as -ij in yušij “related to, belong to Yu&#353 (a famous village in Mâzandarân),” and in the dialect of Boyin-Zahra dehij “villager, peasant, rustic” from deh “village.”

In recent years -ik has been reactivated in technical terminology to render E. -ics (Fr. -ique, Ger. -ik), as in the following examples:

âvâyik “phonetics;” farmânik “cybernetics;” ma’nâyik “semantics;” nurik “optics;” partâbik “ballistics;” tavânik, niruyik “dynamics;” zabânik “linguistics.”

The revival of -ik is interesting for several reasons, mainly:
a) In the European scientific terminology, branches of science are denoted by two suffixes:

1. -logy, as in biology, geology, mineralogy, etc. The Pers. counterpart of this suffix is the widely used -šenâsi, → -logy;
   
2. -ics, as in biotics, dynamics, kinematics, mathematics, etc. Lacking a Pers. equivalent until recently, -ics was equated with -logy. However, the Pers. suffix -ik produces helpful semantic nuances and allows us new constructions from the same base, for example:
   → biology “zistšenâsi;”
   → biotics “zistik.”
   b) Moreover, in some cases -ik is more efficient than -šenâsi. For example, if we translate ballistics
   by partâbšenâsi,
   how should we render ballistic missile? Mušak-e partâbšenâsi, mušak-e partâbšenâxti, or mušak-e partâbšenâsâné? All these possibilities seem unfitting, and no matter which adjective we choose among them
   the problem remains. The reason is that here ballistic does not really refer to the science (-šenâsi) but points to
   the action of throwing, → ballistic missile. This problem can be turned around using -ik: mušak-e partâbik.
   c) It is not phonetically straightforward in Pers. to make adjectives with the -i suffix from words which end in -i, in particular with -šenâsi. The use of -ik solves this problem and produces adjectives which themselves do not end in -i, for example → astronomical unit “yekâ-ye axtaršnâsik” instead of “~ axtaršnâxti”.

A suffix used to form names of chemical compounds.

See also: From -ide, extracted from Fr. → oxide.

Suffix denoting “family of,” as in Andromedids, Aquarids, Bielids, Draconids, Geminids, Perseids, and so on.

Etymology (EN): Plural form of L. -id-, from -is, Gk. fem. patronymic suffix; or from L. -ides, from Gk. masc. patronymic suffix.

Etymology (PE): -iyân plural form of -i, suffix of relation, adjective + -y- euphonic infix (epenthesis) + -ân plural suffix, as in Haxâmanešiyân “Achaemenids,” Sâsâniyân “Sasanides,” and so on.

1a) A suffix forming the present participle of verbs, e.g. going, observing, writing.

1b) A suffix forming adjectives from participles, e.g. a moving object, a flying bird, a crying baby.

1c) A suffix forming an adjective not derived from a verb, e.g. swashbuckling.

2. A suffix that forms nouns denoting the action of, process of, result of, or something connected with the verb preceding it, e.g. becoming, sleeping, working.

Etymology (EN): 1) M.E. -ing, -inde, from O.E. -ende; cf. Ger. -end, Goth. -and, Gk. -on, L. -ans, Skt. -ant, Av. -ant, Pers. -ân.

2. O.E. -ing, -ung; cf. O.N. -ing, Du. -ing, Ger. -ung.

A suffix denoting several senses, including state or condition, devotion or adherence, principle, doctrine, act, process.

Etymology (EN): From Gk. -ismos, -isma noun suffixes, often directly, often through L. -ismus, -isma, sometimes through Fr. -isme,
Ger. -ismus (all ultimately from Gk.); → -ist.

A suffix of nouns, often corresponding to verbs ending in -ize
or nouns ending in → -ism, that is used to form an agent noun indicating adherence to a certain doctrine or custom, practicing a particular skill or profession, and so on.

Etymology (EN): From Fr. -iste, from L. -ista, from Gk. -istes.

Etymology (PE): -bâvar, from bâvar “belief;” Mid.Pers. wâbar “belief;” Proto-Iranian *uar- “to choose; to convince; to believe;” cf. Av. var- “to choose; to convince” varəna-, varana- “conviction, faith;” O.Pers. v(a)r- “to choose; to convince;” Skt. vr- “to choose,” vara- “choosing.”
-gerâ, from gerâyidan “to incline toward; to intend; to make for,” infinitive of gerâ, the etymology of which is not clear. Gerâ may be a variant of Mod.Pers. kil “bent, inclined” (k/g and l/r interchanges),
from PIE base *klei- “to lean, incline,” cognate with L. clinare “to bend” (E. declination, inclination, etc.), Gk. klinein “to cause to slope, slant, incline,” Skt. sri- “to lean,” O.Pers. θray-, Av. sray- “to lean,” (cf. Ger. lehnen, E. lean).
-gerow, -gerav present stem of geravidan “to believe, confide in; to obey;” Mid.Pers. virrôy(i)stan , related to bâvar, as above, ultimately from Proto-Iranian *uar- (Cheung 2007).
-gar from kar-, kardan “to do, to make” (Mid.Pers. kardan; O.Pers./Av. kar- “to do, make, build;” Av. kərənaoiti “makes;” cf. Skt. kr- “to do, to make;” krnoti “makes,” karma “act, deed;” PIE base k^wer- “to do, to make”).
-mand possession suffix, from Mid.Pers. -omand; O.Pers./Av. -mant; cf. Skt. -mant.

A suffix of adjectives denoting “relating to, characteristic of;” often in adjectives
corresponding to nouns in → -ism or nouns in → -ist.

See also: L. -isticus, from Gk. -istikos, → -ist + → -ic.

1. A noun suffix denoting especially minerals, fossils, explosives, and chemical compounds.
   

2. A suffix denoting a native, inhabitant, adherent, follower, etc.

See also: From Fr. -ite and directly from L. -ita, from Gk. -ites.

A suffix used to form abstract nouns expressing state, degree, or condition: metallicity, luminosity, periodicity, Gaussianity.

Etymology (EN): From M.E. -ite, from O.Fr. -ité, from L. -itas (-itat-), from -i- (thematic or, rarely, connective vowel) + -tas (-tat-), may be cognate with Av./Skt. -tāt (as in Av. uparatāt, Skt. uparátāt “supremacy,” Av. ha^urvatāt, Skt. sarvátāt “completeness”).

Etymology (PE): The suffix -igi, from -ig adj. suffix, variant of -ik,
→ -ic, + -i noun suffix.

Note: The Pers. suffix -i forms state/condition nouns from adjectives, as in: xubi, zešti, râsti, âzâdi, tanhâyi. There is though a phonetic problem when the adj. ends in -i, since two successive i’s are not easily articulable, e.g.: felez “metal,” felezi “metallic,” *felezii “metallicity.” Mid.Pers. did not have this problem, since the adj. suffix was -îg or -îk (instead of -i) and the noun suffix -îh (instead of -i). Some examples in Mid.Pers.:
tuhîg “empty,” tuhîgîh “emptiness,” tuwânîg “able,” tuwânîgîh “ability,” spurrîg “complete,” spurrîgîh “completeness, perfection,” nazdîk “near,” nazdîkîh “proximity.” A way out of this phonetic problem is to use the Mid.Pers. -igi. This solution, first introduced in the case of tohi, tohigi (→ void), was generalized by M. Sch. Adib-Soltâni (Irânigi, Âlmânigi, darunâxtigi, borunâxtigi, etc.). This seems a natural solution since the adj. suffix -i is the evolution of the Mid.Pers. -ig, and
moreover Pers. currently revives the g phoneme in comparable phonetic situations, as in the ending phoneme -é (-eh), which derives from Mid.Pers. -ag. A number of examples: adj. âzâdé, n. âzâdegi; adj. tâbandé, n. tâbandegi; adj. mardâné, n. mardânegi; likewise xâné, xânegi, setâré, setâregân; âzâdé, âzâdegân.
Interestingly, the -igi suffix has this specified function in some dialects, for example (Tajik, Šahrezâ-yi) xâligi “emptiness,” from xâli.

Some examples for the use of -igi in this work: felezigi, → metallicity;
mâddigi, → materiality; beyzigi,
→ ellipcity, tâštigi, → certainty, etc.

1. A suffix occurring in names of → chemical elements, such as → barium, → sodium, → titanium, → uranium. Variant -um, as in → lanthanum.
   

2. It also occurs in names of chemical radicals (ammonium, carbonium) and ions of complex cations (imidazolium, nitrosylium, pyridinium).

See also: From L. suffix forming certain neuter nouns (odium, tedium, colloquium; equilibrium, millennium; collegium, consortium), from Gk. -ion.

A suffix forming adjectives from verbs expressing tendency, disposition, function, connection, etc.: active; corrective; destructive; detective; passive; sportive.

Etymology (EN): From L. -ivus, but sometimes from O.Fr. -if.

Etymology (PE): -i and -andé current suffixes.

A verb-forming suffix occurring originally in loanwords from Gk. that have entered English through L. or Fr.

Etymology (EN): From M.E. -isen, from O.Fr. -iser, from L.L. -izare, from Gk -izein.

Etymology (PE): -idan, -astan infinitive suffixes; kardan “to do, to make,” auxiliary verb of compound verbs
(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”).

An adjective suffix meaning “without.”

Etymology (EN): M.E. -les, from O.E. -leas, from leas “free (from), devoid (of), false;” cf. Du. -loos, Ger. -los “-less,” , O.N. lauss “loose, free, vacant,” M.Du. los, Ger. los “loose, free,” Goth. laus “empty, vain.”

Etymology (PE): Bi- privative prefix, → a-.

A diminutive, noun-forming suffix (booklet; platelet).

Etymology (EN): M.E., from M.Fr. -elet, from L. -ellus + M.Fr. -et, from L. -ittus, both diminutive suffixes.

Etymology (PE): -Cé diminutive suffix, from Mid.Pers. -cak, variants -êžak (as in kanicak “little girl,” sangcak “small stone,” xôkcak “small pig”), also Mod.Pers. -ak.

Resembling or similar to. → spacelike, → timelike; → solar-like star.

Etymology (EN): A suffixal use of like " of the same form, appearance," in the formation of adjectives, from M.E. lic, lik, shortening of O.E. gelic “like, similar;” cf. O.S. gilik, Du. gelijk, Ger. gleich “equally, like.”

Etymology (PE): -sân suffix of similarity, from sân “way, manner.”
-vâr a suffix meaning “resembling, like,” from Mid.Pers. -wâr; Av. -vara, -var; cf. Skt. -vara.
-mânand, suffix from mânand, → similar.

A combining form used in the names of sciences or bodies of knowledge, such as → biology, → geology, → cosmology. See also → -ics.

Etymology (EN): M.E. -logie, from O.Fr. -logie, from L. -logia, from Gk. -logia, from legein “to speak, tell over; to choose, gather,” logos “word, speech, thought, account.”

Etymology (PE): -Šenâsi, from šenâs, present stem of šenâsidan, šenâxtan “to know, discern, distinguish, be acquainted with;”
Mid.Pers. šnâxtan, šnâs- “to know, recognize,” dânistan “to know;” O.Pers./Av. xšnā- “to know, learn, come to know, recognize;”
cf. Skt. jñā- “to recognize, know,” jānāti “he knows;” Gk. gignoskein “to know, think, judge;” L. gnoscere, noscere “to come to know” (Fr. connaître; Sp. conocer); P.Gmc. *knoeanan; O.E. cnawan; E. know; Rus. znat “to know;” PIE base *gno- “to know.”

1. A suffix forming adverbs from adjectives.
   

2. An adjective suffix meaning “-like.”

Etymology (EN): M.E. -li, -lich(e); O.E. -lic; cf. O.Fris. -lik, Du. -lijk, O.H.G. -lih, Ger. -lich, O.N. -ligr.

Etymology (PE): 1) -âné suffix of adverbs, from Mid.Pers. -ânag.

2. -vâr denoting “resembling, like,” from Mid.Pers. -wâr, Av. -vara, -var; cf. Skt. -vara.
   

A suffix of nouns indicating state, condition, or quality, or
the result or product of an action.

See also: From Fr., from L. -mentum.

A combining form meaning “measure,” used in the names of instruments measuring quantity, extent, degree.

Etymology (EN): From Fr. -mètre; → meter.

Etymology (PE): Suffix -sanj, present stem of
sanjidan “to measure; to compare,” from Mid.Pers. sanjidan “to weigh,”
from present tense stem sanj-, Av. θanj- “to draw, pull;” Proto-Iranian
*θanj-. Other terms from this base in Pers.: lanjidan “to pull up,”
hanjidan, âhanjidan “to draw out,” farhang “education, culture.”

A suffix with the meaning “the process of measuring.”

Etymology (EN): → -meter + -y a suffix used in the formation of action nouns.

Etymology (PE): -sanji, from sanj, → -meter, + -i a suffix of verbal nouns.

A native English suffix attached to adjectives and participles, forming abstract nouns denoting quality and state, such as brightness, cloudiness, compactness, skewness, and so on.

See also: M.E., O.E. -nes(s), cf. M.Du. -nisse, O.H.G. -nissa, Ger. -niss.

A combining form denoting a system of laws governing or sum of knowledge regarding a specified field. → astronomy, → economy.

Etymology (EN): From Gk. -nomia “law,” from nomos, related to nemein “to distribute, allot, arrange.”

Etymology (PE): Dât, dâd “law, justice;” dâti, from Mid.Pers. dâtik, dâdig “related to law, legal,” from from O.Pes./Av. dāta- “law,” from dā- “to put, make, create;” cf. Skt. dhā- “to put, to place;” Gk. tithemi “to put down, to place;” L. fecit “made;” E. do, deed; PIE *dhe- “to put, to place;” -ik, → ics;
-šenâsi, → -logy; -nâmusi, from nâmus loan from Gk. -nomos, as above.

A suffix meaning “like, resembling,” used in the formation of adjectives and nouns; e. g. asteroid, cycloid, ellipsoid.

Etymology (EN): From Gk. -oeides, from eidos “form,” related to idein “to see,” eidenai “to know;” PIE *weid-es-, from base *weid- “to see, to know;” cf. Pers. bin- “to see” (present stem of didan); Mid.Pers. wyn-; O.Pers. vain- “to see;” Av. vaēn- “to see;” Skt. veda “I know.”

Etymology (PE): Suffix -vâr denoting “resembling, like,” from Mid.Pers. -wâr, Av. -vara, -var, cf. Skt. -vara.

1. Suffix used in the names of subatomic particles (electron, proton, neutron, gluon, etc.), quanta (photon, graviton, etc.), and other minimal entities or components.
   
2. Suffix used in the meaning of inert gases (e.g. neon, krypton).

See also: 1) Probably extracted from → ion.
2) From Gk. -on, neuter of -os adj. ending.

A suffix forming agent nouns, occurring originally in loanwords from Anglo-French; it now functions in E. as an orthographic variant of -er.

Etymology (EN): From M.E., from O.Fr. -o(u)r, from L. or-, extracted from -tor; Gk. -tor (e.g. dotor “giver,” genetor “begetter,” ktistor “founder”); cf. Av. -tar- (dātar- “giver,” astar- “thrower,” baxtar- “tributor”); Skt. -tr- (kartr- “doer,” dhātr- “founder,” astr- “thrower”).

Etymology (PE): Agent suffix -gar, variant -gâr, -kâr,
from kar-, kardan “to do, to make” (Mid.Pers. kardan; O.Pers./Av. kar- “to do, make, build;” Av. kərənaoiti “makes;” cf. Skt. kr- “to do, to make;” krnoti “makes,” karma “act, deed;” PIE base k^wer- “to do, to make”).
Suffix -âr, as in parastâr, xaridâr, foruxtâr, virâstâr, xâstâr, nemudâr. Agent suffix -andé, used with verbs.

A suffix forming adjectives that have the general sense “possessing, full of, inclined to.” Variant -ious.

See also: M.E., from O.Fr. -ous, -eux, from L. -osus.

A combining form meaning “lover of, attracted to” that specified by the initial element.

Etymology (EN): -phile, also -phil, from M.L. -philus, from Gk. -philos, common suffix in personal names (such as Theophilos), from philos “loving, dear,” from philein “to love,” which is of unknown origin.

Etymology (PE): -dust, from dust “friend; lover;” Mid.Pers. dôst “friend;” O.Pers. dauštar- “friend;” Av. zaoša- “pleasure,” zuš- “to like,” zušta- “loved;” cf. Skt. jos- “to like, be pleased, enjoy,” jósa- “satisfaction,” jóstar- “loving;” Gk. geuomai “to taste;” L. gustare “to taste.”

A suffix meaning “instrument for viewing,” used in the formation of compound words, such as → telescope, → microscope; → spectroscope.

Etymology (EN): N.L. -scopium, from Gk. -skopion, -skopeion, from skopein “to behold, look, consider,” skeptesthai “to look at;” PIE base *spek- “to see;” cf. Av. spasiieiti “looks at, perceives,” spas- “spy;”
Skt. paś- “to see, watch,” spasati “sees;” L. specere “to look at;” O.H.G. spehhon “to spy,” Ger. spähen “to spy.”

Etymology (PE): -bin, short for binandé “seer,” present stem of didan “to see,” from
Mid.Pers. wyn-; O.Pers. vain- “to see;” Av. vaēn- “to see;”
cf. Skt. veda “I know;” Gk. oida “I know,” idein “to see;” L. videre “to see;” PIE base *weid- “to know, to see.”
-nemâ, present stem of nemudan “to show;” Mid.Pers. nimūdan, nimây- “to show,” from O.Pers./Av. ni- “down; into,” → ni- (PIE),+ māy- “to measure;” cf. Skt. mati “measures,” matra- “measure;”
Gk. metron “measure;” L. metrum; PIE base *me- “to measure.”

A suffix used to form abstract action nouns corresponding to nouns with stems ending in → -scope.

Etymology (EN): From Gk. -skopia, → -scope + -ia.

Etymology (PE): -bini, from -bin, → -scope, + -i noun suffix.

A combining form used in the names of devices that stabilize or make constant what is specified by the initial element, e.g. → cryostat; → thermostat.

Etymology (EN): From Gk. -states, from sta- stem of histanai
“to make stand,” histemi “put, place, weigh,” stasis “a standing still;” L. stare “to stand;” Pers.
ist “to stand; to be standing, “from istâdan “to stand;” Mid.Pers. êstâtan; O.Pers./Av. sta- “to stand, stand still; set;” Av. hištaiti; cf. Skt. sthâ- “to stand;” PIE base *sta- “to stand.”

Etymology (PE): Suffix -pâ, -pây present stem of pâyidan “to stand firm, to be constant, steady,” from Mid.Pers. pattây-, pattutan “to last, endure, stay.”

A suffix used to form abstract nouns from verbs to express action, state, or associated meanings.

Etymology (EN): From L. -tionem, accusative of noun suffix -tio (genitive -tionis).

Etymology (PE): -eš, from Mid.Pers. -išn.

A suffix forming personal agent nouns mainly from verbs, as in dictator, genitor, orator.

Etymology (EN): From L. -tor (examples), cf. Gk. -tor (examples), Av. -tar (astar “thrower,” dātar- “giver,” varštar- “producer”),
Skt. -tr (datr- “giver,” dartr- “breaker”)

Etymology (PE): Agent suffix -gar, variant -gâr,
from kar-, kardan “to do, to make” (Mid.Pers. kardan; O.Pers./Av. kar- “to do, make, build;” Av. kərənaoiti “makes;” cf. Skt. kr- “to do, to make;” krnoti “makes,” karma “act, deed;” PIE base k^wer- “to do, to make”).
Suffix -âr, as in parastâr, xaridâr, virâstâr. Agent suffix -andé, used with verbs.

A suffix used principally in the names of various devices and instruments (klystron; magnetron; cyclotron; synchrotron).

See also: Perhaps a shortening of electron with accidental allusion to the Gk. instrumental suffix -tron, as in arotron “plough;” akin to O.E. -thor, suffix denoting an instrument; L. -trum; Skt. -tra.

A suffix denoting “turned toward” that specified by the initial element; → barotropic, → isotropic, → polytropic.

Etymology (EN): From Gk. -tropos “a turn, way, manner,” from tropein “to turn,” from PIE base *trep- “to turn” (cf. L. trepit “he turns”).

Etymology (PE): Gard “turning, changing,” from gardidan “to turn, to change,” Mid.Pers. vartitan, Av. varət- “to turn, revolve,” Skt. vartati, L. vertere, O.H.G. werden “to become;” PIE *werto, *wer-.

A suffix denoting the state of turning in a specified way.

Etymology (EN): From Gk. -tropia, from tropos “turn,” trope “a turning.”

Etymology (PE): Suffix form -gardi, from gardidan, gaštan “to turn, to change” (Mid.Pers. vartitan; Av. varət- “to turn, revolve;” Skt. vrt- “to turn, roll,” vartate “it turns round, rolls;” L. vertere “to turn;” O.H.G. werden “to become;” PIE base *wer- “to turn, bend”).

A suffix meaning “small, little,” as in → formula, → globule, → module, capsule, nodule.

Etymology (EN): From Fr. -ule, from L. diminutive suffix -ulus (feminine -ula, neuter -ulum).

Etymology (PE): Pers. diminutive suffix -ul, ulé, as in:
zangulé, zangul “small bell;”
kutulé, kutul “dwarf;”
golulé, gullé “small ball; bullet;”
maškulé (Torbat Heydariye-yi) “small water-skin;”
kandulé “a small jar for holding grain;”
jâšulé = small donkey (Kurd.);
Ahmadulé = little Ahmad (Kurd.);
rulé = “little child” (Kurd., Tâleši, Borujerdi, Malâyeri,
and other Western dialects of Iran) probably from *ruduleh, cf. rud “child” (in zâd-o-rud) and Gilaki rey “boy;”
digul (Šuštari), digulé (Qomi) “small casserole, little pot;”

This suffix occurs also as -ulu, -âlé, and -élé as, e.g., in
kuculu, cangul, panjul, bozqâlé, dâsqâlé,
kâselé (Farâhâni) “small bowl,” and
barfelé (Farâhâni) “little snow.”

Examples of use in this dictionary:
disul → formula;
karpul → corpuscle.

See also -al → -al

A suffix denoting spatial or temporal direction, as specified by the initial element. Also -wards (Dictionary.com).

Etymology (EN): M.E., from O.E. -weard “toward,” literally “turned toward;” PIE *wert- “to turn, wind,” from *wer- “to turn, bend;” cf. Pers. gard-, gardidan “to turn, change,” → revolve, → evolve.

Etymology (PE): -su, → direction.

The forces of jets from a comet’s nucleus that can cause a rocket-like effect and alter a comet’s direction of motion slightly.

See also: → non-; → gravitational; → force.

A dark lane that appears behind the coma in some comets. It is not the shadow of the true nucleus but sometimes may be a region of the near-tail that lies behind the densest part of the inner coma and therefore receives less sunlight.

See also: → shadow; → nucleus.

A → trans-Neptunian object located in the → Kuiper belt, nicknamed Ultima Thule. It is elongated in shape with estimated dimensions of about 31 by 19 km. NASA’s → New Horizons spacecraft conducted a close → flyby of the object on January 1, 2019 just 3,500 km above the object’s surface. The images it took show that the object has in fact two distinct lobes.

At a heliocentric distance of 44 → astronomical units, (486958) 2014 MU₆₉ is the most distant object ever visited by a spacecraft.

It has an → orbital period of 298 years, a small → inclination (~ 2.45°), and a low → eccentricity (0.042).

See also: → asteroid designation.

The → fine structure → emission line of → carbon at 157.74 μm, with transition ²P_3/2-²P_1/2 (rest frame frequency 1900.54 GHz). [C II] is a major → cooling line in → molecular clouds and is produced in low density → photodissociation regions (PDRs)
(n_H≤ 10³ cm^-3). In higher density PDRs the [O I] 63 μm line becomes an important → coolant. The [C II] line traces → neutral gas exposed to → ultraviolet  → photons from → young stars. The [C II] line is used to probe the stellar → radiation field and find out how
it affects the physical conditions of the gas. The bulk of the [C II] emission line is believed to originate from PDRs, and the remainder from → X-ray Dissociation regions (XDRs), and, in a lesser extent, by cosmic-ray-dominated regions (CRDRs), → H II regions, low-density warm gas and/or diffuse H I clouds.

See also: → carbon; → line.

The two → forbidden lines with → transitions from the upper → energy level  ¹D₂ of the doubly ionized oxygen atom. They occur in the green part of the → visible spectrum and are called → nebular lines. They are λ5006.8 ¹D₂-³P₂ and

λ4958.9 ¹D₂-³P₁.

Theoretical values for the [O III] 5007/4959 line-intensity ratio is 3.01 (Storey and Zeippen, 2000, MNRAS 312, 813).

See also: [O III], spectroscopic notation of the ion O⁺⁺; → doublet.

The fourth largest → main belt asteroid and the only known → asteroid whose surface composition appears similar to that of the dwarf planet Ceres, suggesting a similar origin for these two objects. Hygiea suffered a giant impact more than 2 Gyr ago that is at the origin of one of the largest asteroid families. High angular resolution imaging observations of Hygiea with the VLT/SPHERE instrument (~20 mas at 600 nm) reveal a basin-free nearly spherical shape with semi-axes of 225 ± 5 km, 215 ± 5 km, and 212 ± 10 km and a volume equivalent radius of 217 ± 7 km.

The shape and the best estimate of Hygiea’s mass, (8.32 ± 0.80) × 10¹⁹ kg, yield a density of 1944 ± 250 kg m^-3.

Such density is compatible, within errors, with Ceres’ density (2161.6 ± 2.5 kg m^-3).

These observations moreover, yield a new rotation period of ~ 13.8h for Hygiea, that is half of the currently accepted value. Numerical simulations of the family forming event show that Hygiea’s spherical shape and family can be explained by a collision with a large projectile (Diameter ~ 75-150 km). By comparing Hygiea’s sphericity with that of other solar system objects, it appears that Hygiea is nearly as spherical as Ceres, opening a possibility for this object to be reclassified as a dwarf planet (Vernazza et al., 2019, Nature Astronomy, 28 October).

See also: in Greek mythology Hugieia / Hugeia was a daughter of the god of medicine, Asclepius, and Epione. She was the goddess, personification of health, cleanliness and sanitation. Her Roman name is Hygea/Hygia or Salus.

A → Near-Earth Object (NEO) which is a → B-type asteroid with a ~ 500 m diameter. Bennu completes an orbit around the Sun every 436.604 days (1.2 years) and every 6 years comes very close to Earth, within 0.002 → astronomical units. Bennu’s composition (primitive and carbon-rich), size and proximity to Earth make it the ideal target for the → OSIRIS-REx project. Bennu is officially classified as a potentially dangerous asteroid. In fact, there’s an 0.037 percent (or 1-in-2,700) chance that it will strike Earth in the last quarter of the 22nd century.

See also: Named after the Egyptian mythological bird Bennu.

The largest → near-Earth asteroid, which is about 32 km in size. It belongs to the group of → Amor asteroids and has a → rotation period of about 10.31h.
Ganymed was discovered by Walter Baade on October 23, 1924.

See also: German rendering of → Ganymede. Note that Jupiter’s moon Ganymede is named after the same, but uses a different spelling.

The largest → comet orbiting periodically around the → Sun. Its nucleus is about 26 km across and its orbital period 133 years.

Comet Swift-Tuttle is the parent body of the → meteor shower called the → Perseids.

The comet was discovered in July 1862, when it was apparently as bright as → Polaris in the night sky.

The comet’s reappearance was predictaed for 1992, when it was rediscovered by Japanese amateur astronomer Tsuruhiko Kiuchi.

In 2126 it will be a bright naked-eye comet when it will come within about 23 million km of Earth, or about 60 times the distance from Earth to the Moon. Its nearest approach to Earth is expected in 3044, when the comet will come within 1.6 million kilometres of the Earth’s surface.

See also: Named after the American astronomers who independently discovered the comet in 1862, Lewis Swift (1820-1913) on July 16, and Horace Parnell Tuttle (1837-1923) on July 19.

The prototype of the → Amor asteroids discovered by the Belgian
astronomer Eugène Joseph Delporte (1882-1955) on 12 March 1932. It is about 1 km across, has an → orbital period of 2.66 years, an → aphelion distance of 2.754 → astronomical units, and a → perihelion distance of 1.086 AU.

See also: After the Roman god of love, better known as Cupid.

A → main belt asteroid comprised mostly of metallic iron and nickle (→ M-type asteroid). Psyche is a potato-shaped object with dimensions 279 × 232 × 189 km.
Its average diameter, about 226 km, is about sixteenth the diameter of the → Moon.

Psyche could be an exposed core of an early → planet that lost its rocky outer layers due to a number of violent collisions billions of years ago.

The asteroid revolves around the Sun between the orbits of Mars and Jupiter at a distance ranging from 378 million to 497 million km from the Sun (2.5 to 3.3 Astronomical Units). Its revolution period is 4.99 Earth years and rotates about its axis every 4.196 h.

This asteroid is the primary target of NASA’s Psyche mission. Aimed to launch in August of 2022, the Psyche spacecraft would arrive at the asteroid in early 2026, following a Mars gravity assist in 2023. Over 21 months in orbit, the spacecraft will map and study Psyche’s properties using a multi-spectral imager, a gamma-ray and neutron spectrometer, a magnetometer, and a radio instrument (for gravity measurement). The mission’s goal is, among other things, to determine whether Psyche is indeed the core of a planet-sized object.

See also: Psyche was discovered by Italian astronomer Annibale de Gasparis on March 17, 1852. He named the asteroid for Psyche, the Greek goddess of the soul who was born mortal and married Eros (Roman Cupid), the god of Love.

A → potentially hazardous asteroid of the → Apollo group.

It is approximately 900 m across and displays the characteristics of → C-type asteroids. It was discovered by astronomers with the Lincoln Near-Earth Asteroid Research on May 10, 1999. Ryugu rotates every ~ 7.6 hours and

revolves around the Sun in an elongated orbit with an → eccentricity of 0.1902 and a → semi-major axis of 1.1896 → astronomical units (au) in 1.30 years (474 days). Its → aphelion and → perihelion are at 1.4159 au and 0.9633 au, respectively.

Ryugu was visited by the Japanese sample-return spacecraft → Hayabusa2 which arrived at the asteroid on June 27, 2018. It studied the asteroid with its several instruments and landers. It is expected to bring surface material to Earth in 2020.

See also: Provisionally named 1999JU₃, Ryugu was officially adopted by the Minor Planet Center on September 28, 2015.

The name relates to the Japanese folk tale of the fisherman Urashima Taro. He rescues a turtle from a group of children. The turtle takes him to an underwater palace known as “Ryugu” or “Dragon’s Palace.” He falls in love with a princess who begs him to stay, but after three days Urashima wishes to return home. As a parting gift, the princess gives the fisherman a box that she tells him never to open. Upon returning home, Urashima is stunned to find that 300 years have passed and everyone he knew has died. In confusion, he opens the box and is encased in a cloud of white fog. When the fog clears, he finds he is an old man, as the box contained his age.

A → near-Earth asteroid (NEA) that is the prototype of the → Apollo asteroids. It was discovered by the German astronomer Karl Reinmuth (1892-1979) in 1932, but was then lost until 1973. It has an estimated average diameter of 1.4 km, an → orbital period of 652 days, a → perihelion distance of 0.647 AU, and an → aphelion distance of 2.294 AU. It can come as close to Earth as 0.028 AU. Apollo has a small satellite of size less than one-tenth of the primary. Apollo was one of the two first asteroids in which the → YORP effect was detected.

See also: Apollo or Apollon in Greek mythology the god of music and also of prophecy, medicine, archery, poetry, dance, intellectual inquiry and the carer of herds and flocks.

The first known → interstellar object coming from beyond → Solar System. Detected on October 19, 2017 by the → Pan-STARRS sky survey, it was initially classified as an interstellar → asteroid.

‘Oumuamua has a strongly → hyperbolic orbit (→ eccentricity 1.191 ± 0.007), with a very high average velocity with respect to the Sun (v_∞ = 26.32 km s^-1), indicating that it likely originated from beyond our Solar System. Its → inclination with respect to the → ecliptic is 123°. ‘Oumuamua would be approximately 160 m in diameter.
This is the first known asteroid-like energetically unbound from the Sun. By comparison the → NASA Voyager 1 spacecraft travels about 17 km s^-1 through → interstellar medium.

When first detected, ‘Oumuamua was 0.2 → astronomical units (au) from the Earth (30 × 10⁶ km). Initially it was classified to be a → comet and was designated C/2017 U1. But further observations revealed no hint of → cometary activity. The object was therefore reclassified as an asteroid with designation A/2017 U1.

According to orbit calculations, ‘Oumuamua
crossed under the → ecliptic plane just inside of Mercury’s orbit and then went through → perihelion on September 9, 2017, at a distance of 0.25528 au (about 38 million km) from the Sun, speeding up to 87.71 km s^-1.

Pulled by the Sun’s gravity, the object made a U turn below the ecliptic, passing under Earth’s orbit on October 14 at a distance of about 24 million km, that is about 60 times the distance to the Moon. It has now risen above the plane of the planets and is travelling at 44 km s^-1 with respect to the Sun. In 2197 it will be 1,000 au from the Sun.

Recent → outgassing activity observed toward this object suggests that ‘Oumuamua is most likely an interstellar comet and not an asteroid (Michelli et al., 2018, Nature 27 June).

See also: The name ‘Oumuamua approved by the IAU was submitted by the team at the Pan-STARRS telescope who discovered the object. It is a Hawaiian construct combining ‘ou “to reach out” and mua “first” or “in advance of;” the second mua is for emphasis.
‘Oumuamua is loosely translated as “scout” or “messenger.” The 1I prefix indicates the interstellar nature of this first object.

The largest → asteroid and the second to be discovered, by Heinrich Olbers in 1802. Before the reclassification of → Ceres,
Pallas was the second largest asteroid. Pallas is slightly irregular in shape with dimensions 570 x 525 x 482 km. It appears to have the same composition as → meteorites classed as low-grade → carbonaceous chondrites. Its → rotation period is 9 to 12 hours, and its → semi-major axis 2.773 → astronomical unints.

See also: In Gk. mythology, Pallas was one of the Titans. The winged husband of Styx, he is the father of Nike and maybe Eos. Some legends claim that he is the father of Athena, possibly because of her nickname Pallas-Athena.

A new → dwarf planet found beyond Pluto’s
orbit, in the → Kuiper belt. It is roughly 700 km in size and has a highly elliptical orbit; it seems to come as close to the Sun as 34 → astronomical units (AU), and farther away than 120 AU. 2015 RR245 was discovered by an international team of astronomers using the Canada-France-Hawaii Telescope on Maunakea.

See also: A provisional name.

The smallest → near-Earth asteroid (NEA) ever characterized in detail. 2015 TC25 is also one of the brightest NEAs ever discovered, since the object reflects about 60% of the incident sunlight. 2015 TC25 was observed using ground-based optical, → near-infrared and radar techniques during a close → flyby 126,000 km from the Earth in Oct. 2015. The observations suggest that its surface composition is similar to → aubrites, a rare class of high albedo → differentiated meteorites. 2015 TC25 is also a very fast rotator with a → rotation period of 133 seconds. There are clues that 2015 TC25 was chipped off by another impacting rock from its parent, → (44) Nysa, a large and bright → main belt asteroid that measures about 80 km in diameter (Reddy et al., 2016, arXiv:1612.00113).

See also: Provisional name for an → asteroid designation whose orbit is not know.

The first → asteroid found to have an orbital → semi-major axis of less than one → astronomical unit. Discovered by the American woman astronomer Eleanor F. Helin (1932-2009) in 1982, it is the prototype of the → Aten asteroids.

See also: Named after Aten, the Egyptian god of the solar disk.

The → emission line of → neutral hydrogen in → interstellar clouds. It lies in the → radio spectrum at → wavelength of about 21 cm, → frequency 1420 MHz. Its existence was predicted by Hendrik van de Hulst in 1944 and discovered by Harold Ewen and Edward Purcell in 1951.

See also: Twenty-one (21); → twenty + → one; → centimeter; → line.

The → emission line of → neutral hydrogen in interstellar clouds. It lies in the radio spectrum at wavelength of about 21 cm, frequency 1420 MHz. Its existence was predicted by Hendrik van de Hulst in 1944 and discovered by Harold Ewen and Edward Purcell in 1951.

See also: Twenty-one (21); → twenty + → one; → centimeter; → line.

The strongest spectral feature in the interstellar → extinction curve occurring in the → ultraviolet and centered at about 2175 Å. The feature is a strong function of the → metallicity of the gas. It appears slightly weaker in the → LMC extinction curve (metallicity about 50% solar), but essentially absent in the → SMC extinction curve (metallicity about 10% solar). Small → interstellar  → graphite  → dust grains or a mixture of graphite and → polycyclic aromatic hydrocarbons (PAHs) grains have been proposed in → dust models to explain the bump. However, at present the → carrier of the 2175 Å feature is basically unidentified.

See also: → angstrom; → bump.

A blue star of → apparent visual magnitude 4.96 lying in the → Orion constellation. It has other designations, including: ψ¹ Orionis, BD+01 1005, HR 1789, and HIP 25302. 25 Ori is a → main sequence star of → spectral type B1 V.

It lies at a distance of 1,040 → light-years and has a → luminosity of 9,300 MSun, a radius of 5.5 Rsun, and a mass of about 10 Msun.

25 Ori is in fact a → <i><a class="linkVoir" href="/terms/be-star/">Be star</a></i>.

A group of nearly 200 low-mass → pre-main-sequence stars, concentrated within ~ 1 of the early → B star  → 25 Orionis, in the component a of the → Orion OB1 Association. The group also harbors the → Herbig Ae/Be star V346 Ori and a dozen other early-type stars. The velocity distribution for the low-mass stars shows a narrow peak at 19.7 km s^-1, offset ~ 10 km s^-1 from the velocity characterizing the younger stars of the Ori OB1b subassociation, and 4 km s^-1 from the velocity of widely spread young stars of the Ori OB1a population. This indicates that the 25 Ori group is a distinct kinematic entity. The low-mass members follow a well-defined band in the → color-magnitude diagram, consistent with an age of ~ 7-10 Myr (Briceno et al., 2007, ApJ 661, 1119).

See also: → 25 Orionis; → group.

A → main belt → S-type asteroid of size about 51 km. Its → semi-major axis is 2.198 → astronomical units and its orbital period 3.26 yr. It was discovered by C. H. F. Peters on October 8, 1887.

See also: Name of an Iranian female deity, → Venus.

A new → interstellar object of → cometary nature.

Orbital and morphological properties of this body show that this is the first certain case of an interstellar comet, and the second-known interstellar minor body identified in the → Solar System (after → 1I/‘Oumuamua).

2I/Borisov’s motion shows significant systematic deviation from what is expected for a → parabolic orbit and is consistent with an enormous orbital → eccentricity of 3.14 ± 0.14. Images show an extended → coma and a faint, broad → tail. The → color index of 0.63 ± 0.03 is essentially the same as measured for the native Solar System → long-period comets.

2I/Borisov will reach its → perihelion on 7 December 2019, when it will be 2 → astronomical units (AU) from the Sun and also 2 AU from Earth. By January 2020 it will be at its brightest in the southern sky. It will then begin its outbound journey, eventually leaving the Solar System forever

(Guzik et al., 2019, Nature Astronomy, 14 October).

See also: Named after the amateur astronomer Gennady Borisov, from MARGO observatory, Crimea, who on 30 August 2019 discovered an object with a comet-like appearance.

Same as → Tarantula Nebula.

See also: 30 (→ thirty), the object number in the catalog of Johann Elert Bode
(1747-1826) Allgemeine Beschreibung und Nachweisung der Gestirne nebst Verzeichniss, compiled in 1801; → Dorado.

An → Apollo asteroid with unusual properties. Phaethon was discovered on October 11, 1983 using the → Infrared Astronomical Satellite.
It is dynamically associated with the → Geminid meteor shower. Whereas most established → meteor shower
parents are clearly → cometary in nature, the orbit of Phaethon is that of an → asteroid . Its → semi-major axis, → eccentricity, and → orbital inclination are a = 1.271 AU, e = 0.890, and i = 22.2, respectively, and the → Tisserand parameter with respect to → Jupiter is T_J = 4.5 (while the conventional → comets have T_J < 3). The → perihelion distance is remarkably small, q = 0.14 AU. Phaethon is roughly 5 km in diameter. Not to be confounded with → Phaeton.

See also: Named after the Greek myth of Phaethon, son of the Sun god Helios, due to its close approach to our Sun.

A catalog (Bennett, 1962) based on the original 3C survey (Edge et al., 1960) made at Cambridge at 159 MHz using a complex → interferometer system. This → survey was preceded by the 2C survey made with the same instrument at 81 MHz with a resolution two times poorer. The 2C catalog contained 1936 sources, but owing to the poor resolving power, it became clear at an early stage that many of these sources were not real, and were due to blends of two or more sources in the primary antenna beam. Moreover, except for the strongest sources, the determination of the flux density and angular coordinates was poor. The 3C survey contained only 471 sources and was considerably more reliable. Nevertheless, because of the relatively poor primary resolving power, there were still large errors in the positions and flux densities. In particular, it was frequently uncertain in which → lobe of the → interference pattern a particular source was located, and this introduced large positional uncertainties.

In order to reduce these uncertainties an additional survey was made at 178 MHz using a large parabolic cylinder antenna. The narrow E-W beam of this antenna eliminated nearly all of the lobe ambiguities of the original 3C catalog. The data from the two surveys were combined to form the then most reliable radio source catalog - the Revised 3C or 3CR Catalogue. The same parabolic cylinder antenna was later used together with a smaller moveable antenna as an aperture synthesis instrument to make a complete high-resolution survey of the northern sky (the 4C survey), which contains about 2000 sources (NASA/IPAC Extragalactic Database, NED).

See also: 3, for the third “version;” C, for “catalog;” R, for “revised;” → catalog.

A blue star with → apparent visual magnitude 4.59 in → Orion’s Sword. Also known as → c Orionis, HD 37018, HR 1892, and HIP 26237. More specifically, it is a → main sequence star of → spectral type B1 V, lying in the → H II region→ NGC 1977. 42 Orionis is approximately 900 → light-years away based on parallax. It is the major source for ionizing photons in NGC 1977. 42 Ori is a → mutiple star system. The primary star, Aa, of magnitude 6.3 has a → companion companion Ab at a separation of 0.16’’, and a more distant companion B of 7.5 magnitude at 1.6’’ separation.

An irradiated → circumstellar disk near 42 Ori has been detected by Bally et al. (2012) in the → HST image using Hα filter (F658N). They identified a bent → protostellar jet HH1064 from Parenago 2042 (the Spindle) in NGC 1977 with numerous → bow shock features. They argue that the arc feature in the Hα Spindle is centered on the star and its brightened side of the arc is facing toward 42 Ori, suggesting that it may be a → proplyd (Kim et al., 2016, arXiv::1606.08271).

See also: Number 42 in → Flamsteed designation; Orionis, genitive of → Orion.

An → S-type asteroid about 34.4 × 11.2 × 11.2 km in size, which is the second-largest → near-Earth asteroid after 1036 Ganymed. It belongs to the group of → Amor asteroids. Eros was discovered on 13 August 1898 by Gustav Witt in Berlin and Auguste Charlois at Nice. It was the first asteroid orbited by an Earth probe (in 2000).

See also: Named after the Gk. god of love Eros.

The largest member of a rare class of → asteroids with a high surface → albedo, classified as an → E-type. It has an albedo of about 0.5, and is irregularly shaped, 113 × 67 × 65 km. Nysa has an → aphelion of 2.782 → astronomical units and a → perihelion of 2.064 AU. The → eccentricity is 0.15 with an → inclination of 3.70 degrees. The → orbital period is 1,378 days, or 3.77 years. It rotates in 6.42 h. The apparent magnitude ranges from 8.83 to 12.46. Nysa’s orbit makes it the largest E-type asteroid inside Jupiter’s resonance orbits. Nysa was discovered by Hermann Goldschmidt on May 27, 1857.

See also: Named after the birthplace of Dionysus in Greek mythology.

The second brightest → globular cluster, after → Omega Centauri. It is seen on the sky near the → Small Magellanic Cloud in the southern constellation → Tucana. Its apparent size is 31’, about the size of the full Moon. It is about 13,000 → light-years away and contains several million stars in a volume only about 120 light-years across.

See also: 47, the object number in the catalog of Johann Elert Bode (1747-1826) Allgemeine Beschreibung und Nachweisung der Gestirne nebst Verzeichniss, compiled in 1801; → Tucana.

A → trans-Neptunian object located in the → Kuiper belt; provisional designation 2014 MU₆₉ and nicknamed Ultima Thule.

Its overall dimensions are about

36 × 18 × 10 km. NASA’s → New Horizons spacecraft conducted a close → flyby of the object on January 1, 2019 just 3,500 km above the object’s surface. The images it took show that the object has in fact two distinct lobes.

The individual lobes have approximate dimensions of 21 × 20 × 9 km and 15 × 14 × 10 km, respectively.

At a → heliocentric distance of 44 → astronomical units, 486958 Arrokth is the most distant object ever visited by a spacecraft.

It has an → orbital period of 298 years, a small → inclination (~ 2.45°), and a low → eccentricity (0.042).

See also: Arrokoth is a Native American term meaning “sky” in the Powhatan language of the Tidewater region of Virginia and Maryland; → asteroid designation.

A → binary star in the → constellation  → Cygnus lying at a distance of 11.4 → light-years. It consists of a pair of → K-type  → dwarf stars. The more massive component (61 Cygni A) is a K5 type with a mass of 0.70 Msun and the other one (61 Cygni B) a K7 type of 0.63 Msun. The components of this → visual binary orbit each other in a → period of about 659 years. 61 Cygni was the first star whose distance was measured using its → annual parallax. It was done by the German astronomer Friedrich Bessel in 1838 who derived a parallax of 0".314. Recent more precise observations with the → Hipparcos satellite give a value of 0".286. Same as → Bessel’s star and → Piazzi’s Flying Star.

See also: 61 Cygni, according to the → Flamsteed designation; → Cygnus.

A large, bright → main belt asteroid. With a diameter of 136 km, it is the innermost of large → asteroids and the largest member of the → Flora family. It revolves around the Sun with an → orbital period of 3.27 years between a → perihelion of 1.858 → astronomical units and an → aphelion of 2.546 AU. Flora was discovered by J. R. Hind on October 18, 1847.

Etymology (EN): The name Flora was proposed by John Herschel, from Flora, the Latin goddess of flowers and gardens, wife of Zephyrus (the personification of the West wind), and mother of Spring.

A → Kuiper belt object discovered in 2004. It has a large satellite named Vanth. Orcus is similar to → Quaoar in size and may be classified as a → dwarf planet.

See also: Named for the ancient Roman god of the underworld, identified with the Greek Pluto, or Hades. The name was chosen because it shares a similar size, orbit, and orbital inclination to that of Pluto.

An elongated → asteroid with dimensions of about 20 × 12 × 11 km. Gaspra is classified as an → S-type asteroid and is likely composed of metal-rich silicates and perhaps blocks of pure metal. It is a member of the → Flora family. It has a → rotation period of 7.04 hours. On October 29, 1991, the → Galileo spacecraft came within 1,600 km of Gaspra. They passed each other at 8 km/s. This was the first time that a spacecraft made a → flyby of an asteroid. Gaspra was discovered by Grigoriy N. Neujamin, Ukrainian astronomer, in 1916.

See also: Named by its discoverer for a resort on the Crimean peninsula that was visited by contemporaries such as Tolstoy and Gorky.

An area on the surface of the → Moon that appears darker and smoother than its surroundings, once thought to be seas, now known to be lava-flooded basins; plural maria.

Etymology (EN): L. mare “sea,” plural form maria, because
Galileo thought the dark featureless areas on the Moon were bodies of water.

Etymology (PE): Daryânemâ literally “looking like a sea,” from daryâ “sea” (Mid.Pers. daryâp variant zrah; O.Pers. drayah-; Av. zrayah- “sea;” cf. Skt. jráyas- “expanse, space, flat surface”)

• nemâ “looking, showing,” present stem of nemudan “to show, display” (Mid.Pers. nimūdan, nimây- “to show,” from O.Pers./Av. ni- “down; into,” → ni-, + māy- “to measure,” → display.