1. A constellation is any grouping of stars in the night sky that forms a recognizable pattern, derived from some mythical or pictorial association.

2. More formally, it is any of the 88 unequal regions into which the celestial sphere is divided by international agreement.

The present constellation boundaries were adopted in 1930 by the International Astronomical Union (IAU) having been drawn up by Eugène Delaporte. They are similar to the rectangular borders of some American states that run exactly north/south or east/west. The constellation boundaries run along lines of declination and right ascension for the epoch 1875 (chosen because this epoch had already been used by Benjamin Gould in defining boundaries for the southern constellations.)

 

Forty-eight of our present-day constellations were identified by Ptolemy in his great Almagest of the second century AD. Coma Berenices was invented by Gerardus Mercator in 1551 by taking a few stars from Leo. A further 12, in the region around the celestial south pole, were staked out by the Dutch explorers Pieter Keyser and Frederick de Houtman and included on a globe of the sky made by Petrus Plancius in 1598 and then in Johan Bayer's Uranometria star atlas in 1603 (see Bayer's constellations). Jakob Bartsch added three constellations in spaces between existing patterns and is also credited with naming Crux, the Cross, by taking four stars from Ptolemy's original Centaurus. Johannes Hevelius contributed seven more in his star atlas of 1687. Finally, in 1750, during a trip to the Cape of Good Hope, Nicolas de Lacaille penciled in the last 14 of our modern constellations to fill in some star-poor regions between existing groups.

 

The stars making up a constellation are not actually bound together in close association but just happen to lie in roughly the same direction as seen from the observer's viewpoint. For example, the five brightest stars in the constellation of Cygnus the Swan (comprising an arrangement also known as the Northern Cross) are approximately 74, 270, 410, 750 and 1600 light-years from the Sun. Moreover, the dimmest of the quintet, Gienah (Epsilon Cygni), lies nearest to the Sun while the brightest, Deneb (Alpha Cygni), is the most remote. Were these two stars to exchange places, Deneb, which is intrinsically one of the most luminous stars visible to the naked eye, would outshine Venus in our night sky.

 

Any future travelers to the stars will quickly grow accustomed to the changing shape of constellations as they cross the interstellar voids. The first groupings to become noticeably distorted from their familiar forms will be those made up largely of nearby stars, such as Cassiopeia (three of the brightest members of which are less than 100 light-years from the Sun) and the Big Dipper (with four stars under 100 light-years away). By contrast, none of the prominent stars in Orion is less than 300 light-years distant and several are between 1,000 and 2,000 light-years from the Sun. Only a very lengthy interstellar voyage would suffice to seriously disturb the Great Hunter's well-known outline.

 

The 88 modern constellations
name	abbreviation	area (deg2)	rank (in area)	origin*	RA (h m)	Dec (°)
Andromeda	And	722	19	1	23 00 to 02 40	+21 to +53
Antlia	Ant	239	62	6	09 25 to 11 05	-24 to -40
Apus	Aps	206	67	3	13 50 to 18 05	-67 to -83
Aquarius	Aqr	980	10	1	20 40 to 00 00	+3 to -24
Aquila	Aql	652	22	1	19 00 to 20 30	+10 to -10
Ara	Ara	237	63	1	16 35 to 18 10	-55 to -68
Aries	Ari	441	39	1	01 40 to 03 30	+10 to +30
Auriga	Aur	657	21	1	04 40 to 07 30	+28 to +55
Bootes	Boo	907	13	1	13 40 to 15 50	+8 to +55
Caelum	Cae	125	81	6	04 20 to 05 10	-27 to -49
Camelopardalis	Cam	757	18	4	03 10 to 14 30	+52 to +87
Cancer	Cnc	506	31	1	07 50 to 09 20	+7 to +33
Canes Venatici	CVn	465	38	5	12 10 to 14 10	+28 to +53
Canis Major	CMa	380	43	1	06 10 to 07 30	-11 to -33
Canis Minor	CMi	183	71	1	07 05 to 08 10	0 to +12
Capricornus	Cap	414	40	1	20 10 to 22 00	-9 to 27
Carina	Car	494	34	6	06 05 to 11 20	-51 to -75
Cassiopeia	Cas	598	25	1	23 00 to 03 00	+50 to +60
Centaurus	Cen	1,060	9	1	11 05 to 15 00	-30 to -65
Cepheus	Cep	588	27	1	20 05 to 00 00	+53 to +87
Cetus	Cet	1,231	4	1	00 00 to 03 25	+10 to -25
Chamaeleon	Cha	132	79	3	07 30 to 13 50	+74 to +83
Circinus	Cir	93	85	6	13 45 to 15 25	-54 to -70
Columba	Col	270	54	4	05 05 to 06 40	-27 to -43
Coma Berenices	Com	386	42	2	12 00 to 13 53	+14 to +34
Corona Austrina	CrA	128	80	1	18 00 to 19 20	-37 to -45
Corona Borealis	CrB	179	73	1	15 15 to 16 25	+26 to +40
Corvus	Crv	184	70	1	11 55 to 13 00	-11 to -25
Crater	Crt	282	53	1	10 50 to 11 55	-6 to -25
Crux	Cru	68	88	4	12 00 to 13 00	-56 to -65
Cygnus	Cyg	804	16	1	19 10 to 22 00	+28 to +60
Delphinus	Del	189	69	1	20 10 to 21 05	+2 to +21
Dorado	Dor	179	72	3	03 50 to 06 40	-49 to -85
Draco	Dra	1,083	8	1	10 00 to 20 00	+50 to +80
Equuleus	Equ	72	87	1	20 50 to 21 25	+2 to +13
Eridanus	Eri	1,138	6	1	01 20 to 05 10	0 to -58
Fornax	For	398	41	6	01 45 to 03 50	-24 to -40
Gemini	Gem	514	30	1	06 00 to 08 05	+10 to +35
Grus	Gru	366	45	3	21 30 to 23 30	-37 to -57
Hercules	Her	1,225	5	1	15 50 to 19 00	+4 to +50
Horologium	Hor	249	58	6	02 10 to 04 20	-40 to -67
Hydra	Hya	1,303	1	1	08 05 to 15 00	-22 to -65
Hydrus	Hyi	243	61	3	01 25 to 04 30	-58 to -90
Indus	Ind	294	49	3	20 30 to 23 30	-45 to -75
Lacerta	Lac	201	68	5	21 55 to 22 55	+33 to +57
Leo	Leo	947	12	1	09 20 to 11 55	-6 to +33
Leo Minor	LMi	232	64	5	09 15 to 11 05	+23 to +42
Lepus	Lep	290	51	1	04 55 to 06 10	-11 to -27
Libra	Lib	538	29	1	14 20 to 16 00	0 to -30
Lupus	Lup	334	46	1	14 15 to 16 05	-30 to -55
Lynx	Lyn	545	28	6	06 20 to 09 40	+34 to +62
Lyra	Lyr	286	52	1	18 10 to 19 30	+26 to +48
Mensa	Men	153	75	6	03 30 to 07 40	-70 to -85
Microscopium	Mic	210	66	6	20 25 to 21 25	-28 to -45
Monoceros	Mon	482	35	4	06 00 to 08 10	-11 to +12
Musca	Mus	138	77	3	11 20 to 13 50	-64 to -74
Norma	Nor	165	74	6	15 25 to 16 35	-42 to -60
Octans	Oct	291	50	6	00 00 to 24 00	-75 to -90
Ophiuchus	Oph	948	11	1	16 00 to 18 40	+14 to -30
Orion	Ori	594	26	1	04 40 to 06 20	-11 to +23
Pavo	Pav	378	44	3	17 40 to 21 30	-57 to -75
Pegasus	Peg	1,121	7	1	21 05 to 00 15	+2 to +37
Perseus	Per	615	24	1	01 30 to 04 50	+31 to +59
Phoenix	Phe	469	37	3	23 20 to 02 25	-40 to -59
Pictor	Pic	247	59	6	04 35 to 06 55	-43 to -64
Pisces	Psc	889	14	1	22 50 to 02 10	-5 to +34
Piscis Austrinus	PsA	245	60	1	21 25 to 23 05	-25 to -36
Puppis	Pup	673	20	6	06 00 to 08 30	-12 to -51
Pyxis	Pyx	221	65	6	08 25 to 09 30	-17 to -38
Reticulum	Ret	114	82	6	03 15 to 04 40	+53 to +67
Sagitta	Sge	80	86	1	18 55 to 20 20	+17 to +22
Sagittarius	Sgr	867	15	1	18 00 to 20 25	-12 to -46
Scorpius	Sco	497	33	1	15 45 to 17 55	-8 to -45
Sculptor	Scl	475	36	6	23 05 to 01 45	-25 to -59
Scutum	Sct	109	84	5	18 15 to 18 55	-4 to -16
Serpens	Ser	637	23	1	15 10 to 16 20 & 17 15 to 18 55	-4 to +20 & -15 to +6
Sextans	Sex	314	47	5	09 -- to 10 50	-11 to +7
Taurus	Tau	797	17	1	03 20 to 06 00	-1 to +31
Telescopium	Tel	252	57	6	18 10 to 20 30	-46 to -57
Triangulum	Tri	132	78	1	01 30 to 02 50	+26 to +37
Triangulum Australe	TrA	110	83	3	15 00 to 17 00	-60 to -70
Tucana	Tuc	295	48	3	22 10 to 01 20	+56 to +75
Ursa Major	UMa	1,280	3	1	08 35 to 14 30	+29 to +73
Ursa Minor	UMi	256	56	1	00 00 to 24 00	+66 to +90
Vela	Vel	500	32	6	08 00 to 11 05	-40 to -57
Virgo	Vir	1,294	2	1	11 35 to 15 10	-22 to +15
Volans	Vol	141	76	3	06 30 to 09 00	-64 to -75
Vulpecula	Vul	268	55	5	19 00 to 21 30	+20 to +30

 

*1 = Ptolemy, 2 = Mercator, 3 = Keyser/de Houtman, 4 = Plancius, 5 = Hevelius, 6 = Lacaille