Science & history · Constellation guide
Cassiopeia, the queen
Cassiopeia's five brightest stars make a W, or an M, depending on the time of night. From mid-northern latitudes the queen circles the pole and never sets.
About this picture
NASA/Goddard Space Flight Center Scientific Visualization Studio. Gaia DR2: ESA/Gaia/DPAC. Constellation figures based on those developed for the IAU by Alan MacRobert of Sky and Telescope magazine (Roger Sinnott and Rick Fienberg). NASA's page (opens in a new tab).
The map is a composite of 1.7 billion catalogued stars, not a photograph from one place: it shows stars far too faint for the eye, and no weather, Moon or city light. It is drawn here in this chart's projection, with each star where it was in 2000; the fastest-moving bright star has shifted about a minute of arc since, far less than a pixel here.
How to spot it: Five bright stars in a W (or M) shape. Source (opens in a new tab)
The W
Five bright stars make a W that writers have compared to a key, a folding door, and a hand stained with henna.
The five brightest stars (opens in a new tab) form a W that Aratus likened to a key or a folding door. Schedar, alpha, takes its name from the Arabic for “the breast”, where Ptolemy placed it; Caph, beta, from the Arabic for “stained hand”, because Arab astronomers saw a hand tattooed with henna here; Ruchbah, delta, from the word for “knee”.
The middle star of the W, Gamma Cassiopeiae (opens in a new tab), is a blue giant giving out as much energy as 34,000 Suns, and it lights up the gas of nearby nebulae such as IC 63, the “Ghost of Cassiopeia”, which needs a large telescope.
In Greek myth she is the vain and boastful queen (opens in a new tab) of Ethiopia, wife of Cepheus and mother of Andromeda; her daughter's constellation lies next to hers.
Sources for this section Ian Ridpath, Star Tales: Cassiopeia (opens in a new tab); NASA Hubble, IC 63 Ghost Nebula (opens in a new tab)
How to find it
From mid-northern latitudes Cassiopeia is up every clear night; from the Southern Hemisphere it is low or absent.
NASA notes (opens in a new tab) that Cassiopeia is visible every clear night from mid-northern and higher latitudes, and that the W is best seen high in the sky on autumn and winter evenings.
By this site's calculation (opens in a new tab), it stands about 69° up in the north at its highest from 40°N, and is highest at about 9 p.m. local time in mid-November. Like every star near the pole it circles the celestial pole (opens in a new tab) through the night, so the W turns on its side and stands on its head as an M; the computed block shows how far south it can be seen at all.
How to see it The W is also a way to the Andromeda Galaxy: the Night Sky Network (opens in a new tab) recommends Cassiopeia, or the Great Square of Pegasus, as the guide. The Andromeda guide gives the steps.
Sources for this section NASA Hubble, IC 63 Ghost Nebula (opens in a new tab); Bright Star Catalogue, 5th Revised Ed. (Hoffleit & Warren 1991), as computed by this site's star engine (opens in a new tab); Preston Dyches, What is the North Star and How Do You Find It?, NASA Science (2021, updated 2024) (opens in a new tab); Kat Troche (Astronomical Society of the Pacific), Catch Andromeda Rising!, NASA Night Sky Network (2024) (opens in a new tab)
Tycho's Star
In 1572 a new star blazed in the W, as bright as Venus: a supernova.
In November 1572 a bright new star appeared in the W (opens in a new tab), now called Tycho's Star after Tycho Brahe, who published a treatise on it. At its brightest it reached magnitude −4, comparable to Venus, and it stayed visible to the naked eye for more than a year.
It was a supernova. NASA's guide to stars (opens in a new tab) shows the remnant left by the 1572 explosion, about 13,000 light-years away in Cassiopeia, and explains how the collapse of a massive star's core ends in such a blast.
Sources for this section Ian Ridpath, Star Tales: Cassiopeia (opens in a new tab); NASA Science, Star Basics (opens in a new tab)
Cassiopeia A
Another explosion here went unrecorded, and left the youngest known supernova remnant in the Milky Way.
Cassiopeia A (opens in a new tab), about 11,000 light-years away, is the youngest supernova remnant known in our Galaxy; the light of the explosion reached Earth over 300 years ago.
NASA's Chandra X-ray Observatory has imaged it in great depth, and the analysis shows (opens in a new tab) its shock wave accelerating electrons to enormous energies, like a relativistic pinball machine.
Keep in mind Cassiopeia A is an X-ray and radio object. Nothing of it shows to the eye or in a backyard telescope.
Sources for this section NASA Chandra X-ray Observatory, Cassiopeia A (2006) (opens in a new tab)
Where on Earth, and when
The whole key pattern rises from anywhere north of about 26°S.
South of about 33°S, none of it rises.
North of about 33°N, the whole key pattern never sets.
Its middle climbs at least 20° high, the finder's threshold for a suggestion, from anywhere north of about 9°S.
It is highest in the evening sky, at about 9 p.m. local time, in mid-November, from either hemisphere, wherever it rises. With daylight saving time, that is nearer 10 p.m. on the clock.
Worked out by this site from the Bright Star Catalogue, for a flat, clear horizon. Hills, buildings, haze and city light all cut into this; the air also lifts objects near the horizon by about half a degree. For your own place and night, use the sky finder.
Sources
- History Ian Ridpath, Star Tales: Cassiopeia (opens in a new tab) for the W, the names, the myth and Tycho's Star · checked 27 September 2026
- Astronomy NASA Hubble, IC 63 Ghost Nebula (opens in a new tab) for Gamma Cassiopeiae, IC 63 and when the W is best · checked 27 September 2026
- Astronomy Kat Troche (Astronomical Society of the Pacific), Catch Andromeda Rising!, NASA Night Sky Network (2024) (opens in a new tab) for the W as a guide to M31 · checked 27 September 2026
- Astronomy Preston Dyches, What is the North Star and How Do You Find It?, NASA Science (2021, updated 2024) (opens in a new tab) for stars circling the pole · checked 27 September 2026
- Astronomy NASA Science, Star Basics (opens in a new tab) for the 1572 remnant and how supernovae happen · checked 27 September 2026
- Astronomy NASA Chandra X-ray Observatory, Cassiopeia A (2006) (opens in a new tab) for Cassiopeia A · checked 27 September 2026
- Astronomy Bright Star Catalogue, 5th Revised Ed. (Hoffleit & Warren 1991), as computed by this site's star engine (opens in a new tab) for its height from 40°N and best month
