Cygnus

Cygnus Cygni Cyg 804 sq °

History and myth

The Swan is Zeus in the form he took to approach Leda. Its cross of bright stars flies along the Milky Way; Deneb in the tail is one of the most luminous stars visible to the eye, and looks modest only because of its enormous distance.

Data

IAU abbreviation: Cyg
Genitive: Cygni
Area: 804.0 sq °
Catalogue stars: 291
Of those, named: 6
Brightest star: Deneb · 1.25ᵐ
Introduced by: Ptolemy, the Almagest, 2nd century

Stars of the constellation

Star	Apparent magnitude	Distance	Spectral class
Deneb	1.25	3 229 light years	A2Ia
Sadr	2.20	1 524 light years	F8Ib
Aljanah	2.46	72 light years	K0-III
Fawaris	2.87	171 light years	B9.5IV+F1V
Albireo	3.08	386 light years	K3II+B9.5V
Azelfafage	4.67	1 681 light years	B3IV

Messier objects

Designations	Type	Magnitude	Apparent size
M39 · M 39	an open cluster	4.6	32.0′
M29 · M 29	an open cluster	6.6	7.0′

How this sky works

The sky above you right now — or above any city on any night. The horizon, the compass points, sunset and twilight are worked out for the place you choose; the stars, planets and Moon stand where an eye would see them.

The Milky Way itself is the "Deep Star Maps 2020" panorama by NASA's Scientific Visualization Studio, assembled from the Hipparcos, Tycho-2 and Gaia catalogues: every star's colour and brightness come from measurement. On top of it sits our catalogue: 9096 stars down to sixth magnitude, the figures and official boundaries of all 88 constellations, 333 stars with IAU names and the 110 Messier objects. Tap a star and its card opens; tap empty sky and you get the constellation that point belongs to.

The atmosphere and the landscape are drawn, but not made up: the colour of the sky follows how far below the horizon the Sun is, so in the evening the sunset fades first, then the bright stars appear, and only in full astronomical night the Milky Way. The Sun, Moon and planets are computed in the browser from the astronomy-engine ephemerides for your spot on Earth, precession and nutation included.

On a phone, turn on "Point the phone" and the sky on the screen follows wherever you aim it. The place comes from the browser's time zone without asking for any permission; for an exact one use "My location" or search for a city.

Sources

Positions, magnitudes, spectra and proper motions come from the Bright Star Catalogue, 5th ed. (Hoffleit & Warren, 1991). Distances use Hipparcos parallaxes (ESA, 1997): BSC5's own parallaxes predate the satellite and give negative distances for the far stars. Constellation boundaries are Davenhall & Leggett (1989), precessed here from B1875 to J2000. Star names are the official catalogue of the IAU Working Group on Star Names (CC BY). Accessed through the VizieR service, CDS, Strasbourg.

Panorama: NASA/Goddard Space Flight Center Scientific Visualization Studio, Deep Star Maps 2020 (public domain). Catalogues: Bright Star Catalogue, Hipparcos, IAU-CSN, NGC 2000.0. Ephemerides: astronomy-engine. Cities: GeoNames (CC BY).