A

David

Darling

constellation

distances to the stars in Orion

The stars in Orion all look as if they lie at the same distance. Turn the constellation through 90°, however, and the true picture emerges. Credit: ESA

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 abbr. area
(deg2)
rank origin* R.A.
(h m)
dec.
(o )
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