Astronomical map

Alternative titles: astronomical atlas; star atlas; star map


Nature and significance



Telescopic astronomy began in 1609, and by the end of the 17th century, the telescope was being applied in mapping the stars. In the latter part of the 19th century, photography gave a powerful impetus to precise chart making, culminating in the 1950s in the publication of National Geographic Society–Palomar Observatory Sky Survey, a portrayal of the part of the sky visible from Palomar Observatory in California.


The celestial sphere


celestial pole: star trails in Gippsland, Victoria, Australia, with the south celestial pole at the centre [Credit: Collection Mix/Punchstock]celestial pole: star trails in Gippsland, Victoria, Australia, with the south celestial pole at the centreCollection Mix/PunchstockThe daily eastward rotation of Earth on its axis produces an apparent diurnal westward rotation of the starry sphere. Thus, the stars seem to rotate about a northern or southern celestial pole, the projection into space of Earth’s own poles. Equidistant from the two poles is the celestial equator; this great circle is the projection into space of Earth’s Equator.

celestial sphere: celestial coordinates [Credit: ]celestial sphere: celestial coordinatesIllustrated here is the celestial sphere as viewed from some middle northern latitude. Part of the sky adjacent to a celestial pole is always visible (the shaded area in the diagram), and an equal area about the opposite pole is always invisible below the horizon; the rest of the celestial sphere appears to rise and set each day. For any other latitude, the particular part of sky visible or invisible will be different, and the diagram must be redrawn. An observer situated at Earth’s North Pole could observe only the stars of the northern celestial hemisphere. An observer at the Equator, however, would be able to see the entire celestial sphere as the daily motion of Earth carried him around.

constellation: northern sky [Credit: Encyclopædia Britannica, Inc.]constellation: northern skyEncyclopædia Britannica, Inc.In addition to their apparent daily motion around Earth, the Sun, Moon, and planets of the solar system have their own motions with respect to the starry sphere. Since the Sun’s brilliance obscures the background stars from view, it took many centuries before observers discovered the precise path of the Sun through the constellations that are now called the signs of the zodiac. The great circle of the zodiac traced out by the Sun on its annual circuit is the ecliptic (so called because eclipses can occur when the Moon crosses it).

celestial pole: relation to ecliptic pole [Credit: ]celestial pole: relation to ecliptic poleAs viewed from space, Earth slowly revolves about the Sun in a fixed plane, the ecliptic plane. A line perpendicular to this plane defines the ecliptic pole, and it makes no difference whether this line is projected into space from Earth or from the Sun. All that is important is the direction, because the sky is so far away that the ecliptic pole must fall on a unique point on the celestial sphere.



Why the ecliptic and celestial equator meet at an angle of 23.44° is an unexplained mystery originating in the past history of Earth. The angle gradually varies by small amounts as a result of Moon- and planet-caused gravitational perturbations on Earth. The ecliptic plane is comparatively stable, but the equatorial plane is continually shifting as Earth’s axis of rotation changes its direction in space. The successive positions of the celestial poles trace out large circles on the sky with a period of about 26,000 years. This phenomenon, known as precession of the equinoxes, causes a series of different stars to become pole stars in turn. Polaris, the present pole star, will come nearest to the north celestial pole about the year 2100 ce. At the time the pyramids were built, Thuban in the constellation Draco served as the pole star, and in about 12,000 years the first-magnitude star Vega will be near the north celestial pole. Precession also makes the coordinate systems on precise star maps applicable only for a specific epoch.

Celestial coordinate systems

The horizon system


The ecliptic system



The equatorial system

ascension: ascension and declination of a star [Credit: ]ascension: ascension and declination of a starBased on the celestial equator and poles, the equatorial coordinates, right ascension and declination, are directly analogous to terrestrial longitude and latitude. Right ascension, measured eastward from the first point of Aries (see directly above), is customarily divided into 24 hours rather than 360°, thus emphasizing the clocklike behaviour of the sphere. Precise equatorial positions must be specified for a particular year, since the precessional motion continually changes the measured coordinates.

Galactic coordinates


The constellations and other sky divisions

Recognition of the constellations can be traced to early civilization. The oldest astronomical cuneiform texts, from the second half of the 2nd millennium bce, record the Sumerian names of the constellations still known as the lion, the bull, and the scorpion. Drawings of these astronomical animals appear on Babylonian boundary stones of the same period, and the earlier occurrence of these motifs on prehistoric seals, Sumerian vases, and gaming boards suggests that they may have originated as early as 4000 bce. In China a handful of configurations show similarity to those of the West, including the scorpion, the lion, the hunter (Orion), and the northern dipper, suggesting the possibility of a very old common tradition for a few groups but otherwise almost complete independence.


Gazing with fixed eye on the Pleiades,
Boötes setting late and the Great Bear,
By others called the Wain, which wheeling round,
Looks ever toward Orion and alone
Dips not into the waters of the deep.

—Odyssey, V


An’t be not four by
The day I’ll be hanged; Charles’ Wain is over
The new chimney and yet our horse not pack’d.


This form derives from Charlemagne and, according to The Oxford English Dictionary, apparently from a verbal association of the name of the bright nearby Arcturus with Arturus, or Arthur, and the legendary association of Arthur and Charlemagne.

the earliest systematic account of the constellations is contained in the Phaenomena of Aratus, a poet of the 3rd century bce, who described 43 constellations and named five individual stars. Cicero recorded that


De republica, I, 14



Ptolemy divided his stars into six brightness, or magnitude, classes. He listed 15 bright stars of the first magnitude but comparatively few of the faint, much more numerous but barely visible sixth magnitude at the other limit of his list. Al-Ṣūfī, a 10th-century Islamic astronomer, carried out the principal revision made to these magnitudes during the Middle Ages. Ulūgh Beg, grandson of the Mongol conqueror Timur, is the only known Oriental astronomer to reobserve the positions of Ptolemy’s stars. His catalog, put together in 1420–37, was not printed until 1665, by which time it had already been surpassed by European observations.

Constellations of the zodiac

The Mesopotamian arrangement of constellations has survived to the present day because it became the basis of a numerical reference scheme—the ecliptic, or zodiacal, system. This occurred about 450 bce, when the ecliptic was clearly recognized and divided into 12 equal signs of the zodiac. Most modern scholars take the zodiac as a Babylonian invention; the oldest record of the zodiacal signs as such is a cuneiform horoscope from 419 bce. However, as Greek sources attribute the discovery of the ecliptic to Oenopides in the latter part of the 5th century bce, a parallel development in both Greece and Babylon should not be excluded.


The decans



Lunar mansions

Called hsiu in China and nakshatra in India, the lunar mansions are 28 divisions of the sky presumably selected as approximate “Moon stations” on successive nights. At least four quadrantal hsiu that divided the sky into quarters or quadrants were known in China in the 14th century bce, and 23 are mentioned in the Yüeh Ling, which may go back to 850 bce. In India a complete list of nakshatra are found in the Atharvaveda, providing evidence that the system was organized before 800 bce. The system of lunar mansions, however, may have a common origin even earlier in Mesopotamia.

Relationship of the bright stars and their constellations



A unique hemispherical celestial map, which furnishes a remarkable connecting link between the classical representation of the constellations and the later Islamic forms, is painted in the dome of a bathhouse at Quṣayr ʿAmra, an Arab palace built in Jordan about 715 ce. The surviving fragments of the fresco show parts of 37 constellations and about 400 stars.


Tunhuang manuscript [Credit: Courtesy of the trustees of the British Museum]Tunhuang manuscriptCourtesy of the trustees of the British MuseumIf astrolabes are excluded, the oldest existing portable star map from any civilization is the Chinese Tunhuang manuscript in the British Museum, dating from about 940 ce. A Latin document of about the same age, also in the British Museum, shows a planisphere to illustrate the Phainomena of Aratus, without, however, indicating individual stars. The oldest illuminated Islamic astronomical manuscript, a 1009–10 ce copy of al-Ṣūfī’s book on the fixed stars, shows individual constellations, including stars.


New constellations: 16th–20th century




Aries: constellations, from “Uranographia” [Credit: Courtesy of the Observatories, University of Cambridge]Aries: constellations, from “Uranographia”Courtesy of the Observatories, University of CambridgeThe classic atlases of Bayer and Hevelius as well as John Flamsteed’s Atlas Coelestis (1729) showed only the brighter naked-eye stars. Johann Elert Bode’s Uranographia of 1801 was the first reasonably complete depiction of the stars visible to the unaided eye. It included an early use of constellation boundaries, a concept accepted and refined by 19th-century cartographers. Friedrich W.A. Argelander’s Uranometria Nova (1843) and Benjamin A. Gould’s Uranometria Argentina (1877–79) standardized the list of constellations as they are known today. They divided Ptolemy’s largest constellation, Argo Navis (the ship), into four parts: Vela (the sail), Pyxis (the compass), Puppis (the stern), and Carina (the keel).


name genitive form meaning remarks*
Constellations described by Ptolemy: the zodiac
Aries Arietis Ram
Taurus Tauri Bull Aldebaran; Pleiades, M1 (Crab Nebula)
Gemini Geminorum Twins Castor, Pollux
Cancer Cancri Crab Praesepe (star cluster)
Leo Leonis Lion Regulus
Virgo Virginis Virgin Spica; Virgo cluster of galaxies
Libra Librae Balance
Scorpius Scorpii Scorpion Antares; many star clusters
Sagittarius Sagittarii Archer Galactic centre; many star clusters
Capricornus Capricorni Sea-goat
Aquarius Aquarii Water-bearer
Pisces Piscium Fishes
Other Ptolemaic constellations
Andromeda Andromedae Andromeda (Princess) M31 (Andromeda Galaxy)
Aquila Aquilae Eagle Altair
Ara Arae Altar
Argo Navis Argus Navis Ship Argo now divided into Carina, Puppis, Pyxis, and Vela
Auriga Aurigae Charioteer Capella; M36, M37, M38 (open star clusters)
Boötes Boötis Herdsman Arcturus
Canis Major Canis Majoris Greater Dog Sirius (brightest star)
Canis Minor Canis Minoris Smaller Dog Procyon
Cassiopeia Cassiopeiae Cassiopeia (Queen) Tycho’s nova, 1572 (visible in daytime)
Centaurus Centauri Centaur Alpha Centauri (nearest star to Sun), Beta
Cepheus Cephei Cepheus (King) Delta Cephei (prototype for Cepheid variables)
Cetus Ceti Whale Mira (first recognized variable star)
Corona Austrina Coronae Austrinae Southern Crown
Corona Borealis Coronae Borealis Northern Crown
Corvus Corvi Raven
Crater Crateris Cup
Cygnus Cygni Swan "Northern Cross"; Deneb
Delphinus Delphini Dolphin "Job’s Coffin"
Draco Draconis Dragon Thuban (polestar in 3000 BC)
Equuleus Equulei Little Horse
Eridanus Eridani River Eridanus or river god Achernar
Hercules Herculis Hercules (Greek hero) M13 (globular star cluster)
Hydra Hydrae Water Snake
Lepus Leporis Hare
Lupus Lupi Wolf
Lyra Lyrae Lyre Vega; M57 (Ring Nebula)
Ophiuchus Ophiuchi Serpent-bearer
Orion Orionis Hunter Rigel, Betelgeuse; M42 (Orion Nebula)
Pegasus Pegasi Pegasus (winged horse) "Great Square"
Perseus Persei Perseus (Greek hero)
Piscis Austrinus Piscis Austrini Southern Fish Fomalhaut
Sagitta Sagittae Arrow
Serpens Serpentis Serpent
Triangulum Trianguli Triangle M33 (nearby spiral galaxy)
Ursa Major Ursae Majoris Great Bear seven brightest stars are Big Dipper or Plough
Ursa Minor Ursae Minoris Lesser Bear Polaris (the north polestar)
Southern constellations, added c. 1600
Apus Apodis Bird of Paradise
Chamaeleon Chamaeleontis Chameleon
Dorado Doradus Swordfish Large Magellanic Cloud
Grus Gruis Crane
Hydrus Hydri Water Snake
Indus Indi Indian
Musca Muscae Fly
Pavo Pavonis Peacock
Phoenix Phoenicis Phoenix (mythical bird)
Triangulum Australe Trianguli Australis Southern Triangle
Tucana Tucanae Toucan Small Magellanic Cloud
Volans Volantis Flying Fish
Constellations of Bartsch, 1624
Camelopardalis Camelopardalis Giraffe
Columba Columbae Dove constellation formed by Plancius, 1605
Monoceros Monocerotis Unicorn
Constellations of Hevelius, 1687
Canes Venatici Canum Venaticorum Hunting Dogs M51 (Whirlpool Galaxy)
Lacerta Lacertae Lizard
Leo Minor Leonis Minoris Lesser Lion
Lynx Lyncis Lynx
Scutum Scuti Shield
Sextans Sextantis Sextant
Vulpecula Vulpeculae Fox M27 (Dumbbell Nebula)
Ancient asterisms now separate constellations
Carina Carinae Keel [of Argo] Canopus
Coma Berenices Comae Berenices Berenice’s Hair Coma (star cluster); north galactic pole
Crux Crucis [Southern] Cross Acrux, Becrux
Puppis Puppis Stern [of Argo]
Pyxis Pyxidis Compass [of Argo]
Vela Velorum Sails [of Argo]
Southern constellations of Lacaille, c. 1750
Antlia Antliae Pump
Caelum Caeli [Sculptor’s] Chisel
Circinus Circini Drawing Compasses
Fornax Fornacis [Chemical] Furnace
Horologium Horologii Clock
Mensa Mensae Table [Mountain]
Microscopium Microscopii Microscope
Norma Normae Square
Octans Octantis Octant south celestial pole
Pictor Pictoris Painter’s [Easel]
Reticulum Reticuli Reticle
Sculptor Sculptoris Sculptor’s [Workshop] south galactic pole
Telescopium Telescopii Telescope
*First-magnitude stars are given in italics.

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