# Cassiopeia (constellation)
**Cassiopeia** (abbreviation Cas; genitive Cassiopeiae) is a northern constellation representing the Seated Queen, best known for its distinctive five-star "W" asterism that wheels around the north celestial pole near Polaris.[1](https://iauarchive.eso.org/public/themes/constellations/) It is one of the 88 constellations recognized by the International Astronomical Union and one of the 48 ancient Greek patterns recorded by Ptolemy in the *Almagest* in the second century AD.[1](https://iauarchive.eso.org/public/themes/constellations/) • [2](https://www.lutterworth.com/wp-content/uploads/extracts/star-tales-ch1.pdf)
| Key fact | Detail |
|---|---|
| IAU designation | Cassiopeia, abbreviated Cas, "the Seated Queen"; genitive Cassiopeiae, used in star names such as Alpha Cassiopeiae[1](https://iauarchive.eso.org/public/themes/constellations/) |
| Signature pattern | Five bright stars forming a "W" (or "M") asterism; the top of the W faces the North Star[3](https://pwg.gsfc.nasa.gov/stargaze/Spolaris.htm) |
| Visibility | Circumpolar from mid-northern latitudes such as the UK, meaning it never sets and is visible on every clear night[4](https://www.skyatnightmagazine.com/astrophotography/stars/cassiopeia) |
| Best viewing | High in the sky on autumn and winter evenings from mid-northern and higher latitudes[5](https://science.nasa.gov/missions/hubble/hubble-captures-the-ghost-of-cassiopeia/) |
| Notable star | Gamma Cassiopeiae, a second-magnitude Be star about 600 light-years away at the middle of the W, an unusual X-ray source[6](https://science.nasa.gov/missions/hubble/a-new-class-of-x-ray-star/) |
| Famous deep-sky object | Cassiopeia A, a supernova remnant about 11,000 light-years away and roughly 340 years old[7](https://svs.gsfc.nasa.gov//14933) |
| Mythology | Named for the queen of Aethiopia, wife of King Cepheus and mother of Andromeda, punished for boasting[4](https://www.skyatnightmagazine.com/astrophotography/stars/cassiopeia) |
## Pattern and position in the sky
The constellation's five brightest stars trace a zigzag that reads as an "M" when the figure is high in the sky and as a "W" when it swings below Polaris to its lowest point due north.[3](https://pwg.gsfc.nasa.gov/stargaze/Spolaris.htm) • [4](https://www.skyatnightmagazine.com/astrophotography/stars/cassiopeia) • [19](https://earthsky.org/tonight/cassiopeia-high-in-the-north-on-winter-evenings/) Schedar (Alpha Cassiopeiae) takes its name from the Arabic for "breast", marking its position in the heart of the seated Queen figure.[4](https://www.skyatnightmagazine.com/astrophotography/stars/cassiopeia)
**Circumpolar behavior.** Because Cassiopeia lies close to the north celestial pole, it never sets for observers at mid-northern latitudes; from the UK it is visible on every dark, clear night of the year, completing one full rotation around the pole, marked approximately by Polaris, in the course of a night's and a year's turning.[4](https://www.skyatnightmagazine.com/astrophotography/stars/cassiopeia) The Big Dipper and Cassiopeia occupy opposite sides of the pole star, so when one hangs low near the northern horizon, the other stands high in the sky.[3](https://pwg.gsfc.nasa.gov/stargaze/Spolaris.htm)
**A pointer to Polaris.** The W also serves as a wayfinding tool. Polaris sits above the first "V" of the W; a line bisecting the angle of that V and extended onward leads to the vicinity of the pole star.[3](https://pwg.gsfc.nasa.gov/stargaze/Spolaris.htm) [The W](https://www.edgepedia.org/the-w)'s right side can likewise be used as a downward-pointing arrow toward the [Andromeda Galaxy](https://www.edgepedia.org/andromeda-galaxy), our large galactic neighbor.[8](https://www.space.com/stargazing/night-sky-october-2026-what-to-look-for-this-month)
## Mythology and early records
In Greek myth, Cassiopeia was the queen of [Aethiopia](https://www.edgepedia.org/aethiopia), wife of King Cepheus and mother of Princess Andromeda. She was placed in the sky as punishment for boasting that she and Andromeda were more beautiful than the [Nereids](https://www.edgepedia.org/nereids), the sea nymphs.[4](https://www.skyatnightmagazine.com/astrophotography/stars/cassiopeia) Her husband and daughter received neighboring constellations: Cepheus sits above the W's other V, though it is a far less striking figure, and Andromeda's constellation is framed by a large rectangle of four stars.[3](https://pwg.gsfc.nasa.gov/stargaze/Spolaris.htm)
The mythic identification is old. Before [Eratosthenes](https://www.edgepedia.org/eratosthenes) systematized constellation mythology in the third century BCE, only Orion and the group of figures belonging to the [Andromeda](https://www.edgepedia.org/andromeda-mythology) story, namely Perseus, Andromeda, Cepheus, and Cassiopeia, were identified with mythical characters.[9](https://www.early-astronomy-um.org/ancient_eratosthenes.php) Cassiopeia also appears among the 48 constellations Ptolemy cataloged in the *Almagest*.[2](https://www.lutterworth.com/wp-content/uploads/extracts/star-tales-ch1.pdf)
The constellation has a place in the history of star naming as well. When Johann Bayer introduced his Greek-letter scheme in the 1603 atlas *Uranometria*, he used uppercase letters for a few temporary or variable stars, including the letter B for SN 1572, [Tycho Brahe](https://www.edgepedia.org/tycho-brahe)'s supernova in Cassiopeia.[10](https://iauarchive.eso.org/public/themes/naming_stars/)
## Notable stars
**Gamma Cassiopeiae** anchors the middle of the W. It is a second-magnitude star about 600 light-years away and the prototype of a puzzling class of X-ray sources. In the 1860s the Italian priest Father Secchi found bright hydrogen emission in its spectrum, making it the first known member of the "B-emission" (Be) stars, hot stars several times more massive than the Sun known for eruptions of mass.[6](https://science.nasa.gov/missions/hubble/a-new-class-of-x-ray-star/) Simultaneous Hubble Space Telescope and Rossi X-Ray Timing Explorer observations in March 1996 showed that its bright, variable X-rays, with gas at about 100 million degrees, probably come from extraordinarily hot surface flares, repeating with a 27-hour period consistent with the star's rotation; the precise mechanism remains unclear.[6](https://science.nasa.gov/missions/hubble/a-new-class-of-x-ray-star/) Later space photometry confirmed a 203.5-day orbital period for its companion.[11](https://arxiv.org/abs/2002.04646)
[Gamma Cassiopeiae](https://www.edgepedia.org/gamma-cassiopeiae) also lights up surrounding gas. The nebula IC 63, nicknamed the Ghost of Cassiopeia, lies 550 light-years away and glows red as hydrogen bombarded by the star's ultraviolet radiation, with blue light reflected from its dust; the star unleashes as much energy as 34,000 suns, and the surrounding nebulous region spans about two degrees on the sky, roughly four times the width of the full Moon.[5](https://science.nasa.gov/missions/hubble/hubble-captures-the-ghost-of-cassiopeia/)
## Deep-sky objects
Cassiopeia lies along the [Milky Way](https://www.edgepedia.org/milky-way) and is rich in open clusters. The Owl Cluster (NGC 457), also called the E.T. Cluster, sits in the W-shaped constellation and can be spotted with binoculars or a small telescope; its brighter members suggest an owl with two glowing eyes.[12](https://science.nasa.gov/solar-system/skywatching/night-sky-network/feb2024-night-sky-notes/) Caroline's Rose ([NGC 7789](https://www.edgepedia.org/ngc-7789)), another rich open cluster, resolves into hundreds of faint stars in an 8-inch or larger telescope.[13](https://www.space.com/stargazing/what-to-see-night-sky-september-2026) Just across the border, extending a line from Gamma Cassiopeiae through Ruchbah leads to the Double Cluster, the pair of open clusters [NGC 869](https://www.edgepedia.org/ngc-869) and NGC 884, each spanning about 45 arc minutes.[14](https://www.space.com/stargazing/bundle-up-and-look-up-5-winter-sky-wonders-every-stargazer-should-look-out-for)
**Cassiopeia A.** The constellation's most studied object is the supernova remnant [Cassiopeia A](https://www.edgepedia.org/cassiopeia-a) (Cas A), about 11,000 light-years away. The expanding debris cloud spans about 10 light-years, is over 340 years old, and holds a superdense neutron star at its center, the remains of the original star's core.[7](https://svs.gsfc.nasa.gov//14933) When NASA's Chandra X-ray Observatory opened its eye in orbit on 26 August 1999, its first-light images were of Cas A, and they revealed the neutron star for the first time.[15](https://www.nasa.gov/missions/chandra/cassiopeia-a-then-the-cosmos-25-years-of-chandra-x-ray-science/) A James Webb Space Telescope survey in 2022 mapped the remnant's main shell, interior ejecta, and surrounding material in near- and mid-infrared light, describing Cas A as the youngest Galactic core-collapse supernova remnant.[16](https://arxiv.org/abs/2401.02477) In December 2023 the [XRISM](https://www.edgepedia.org/xrism) spacecraft's Resolve instrument made the first clear X-ray detections of chlorine and potassium in the wreckage, finding ratios much higher than expected and concentrated in the southeast and northern parts of the remnant, a lopsided distribution that may reflect asymmetries in the star before it exploded.[7](https://svs.gsfc.nasa.gov//14933)
## Observing highlights
For northern observers, Cassiopeia is a year-round landmark. Its W is best seen high in the sky on autumn and winter evenings.[5](https://science.nasa.gov/missions/hubble/hubble-captures-the-ghost-of-cassiopeia/) In August, the radiant of the Perseid meteor shower lies below the W, in neighboring [Perseus](https://www.edgepedia.org/perseus-constellation), so Cassiopeia serves as a signpost for one of the year's most active meteor displays.[17](https://www.space.com/what-to-see-night-sky-august-2026) In summer, the W skims low along the north-northeast horizon, where it can still guide observers hunting faint targets such as galaxies.[18](https://www.space.com/what-to-see-night-sky-june-2026)
## References
1. [The Constellations, International Astronomical Union](https://iauarchive.eso.org/public/themes/constellations/)
2. [Star Tales, chapter 1 (Ian Ridpath), Lutterworth Press extract](https://www.lutterworth.com/wp-content/uploads/extracts/star-tales-ch1.pdf)
3. [Finding the Pole Star, NASA Goddard Space Flight Center](https://pwg.gsfc.nasa.gov/stargaze/Spolaris.htm)
4. [A guide to Cassiopeia, BBC Sky at Night Magazine](https://www.skyatnightmagazine.com/astrophotography/stars/cassiopeia)
5. [Hubble Captures the Ghost of Cassiopeia, NASA Science](https://science.nasa.gov/missions/hubble/hubble-captures-the-ghost-of-cassiopeia/)
6. [A New Class of X-ray Star?, NASA Science](https://science.nasa.gov/missions/hubble/a-new-class-of-x-ray-star/)
7. [XRISM Finds Elemental Bounty in Supernova Remnant, NASA Scientific Visualization Studio](https://svs.gsfc.nasa.gov//14933)
8. [Night sky October 2026: What to look for in the sky this month, Space.com](https://www.space.com/stargazing/night-sky-october-2026-what-to-look-for-this-month)
9. [Star Mythology: Eratosthenes' Catasterismi, Early Astronomy in the University of Michigan Collections](https://www.early-astronomy-um.org/ancient_eratosthenes.php)
10. [Naming Stars, International Astronomical Union](https://iauarchive.eso.org/public/themes/naming_stars/)
11. [Short-term variability and mass loss in Be stars V: Space photometry and ground-based spectroscopy of γ Cas, arXiv](https://arxiv.org/abs/2002.04646)
12. [February's Night Sky Notes: Constant Companions: Circumpolar Constellations, Part I, NASA Science](https://science.nasa.gov/solar-system/skywatching/night-sky-network/feb2024-night-sky-notes/)
13. [Night sky September 2026: The best things to see this month, Space.com](https://www.space.com/stargazing/what-to-see-night-sky-september-2026)
14. [Bundle up and look up: 5 winter sky wonders every stargazer should look out for, Space.com](https://www.space.com/stargazing/bundle-up-and-look-up-5-winter-sky-wonders-every-stargazer-should-look-out-for)
15. [Cassiopeia A, Then the Cosmos: 25 Years of Chandra X-ray Science, NASA](https://www.nasa.gov/missions/chandra/cassiopeia-a-then-the-cosmos-25-years-of-chandra-x-ray-science/)
16. [A JWST Survey of the Supernova Remnant Cassiopeia A, arXiv](https://arxiv.org/abs/2401.02477)
17. [Night sky August 2026: What you can see tonight, Space.com](https://www.space.com/what-to-see-night-sky-august-2026)
18. [Night sky June 2026: What you can see tonight, Space.com](https://www.space.com/what-to-see-night-sky-june-2026)
19. [Cassiopeia, Queen of the north, Sky Archive, EarthSky](https://earthsky.org/tonight/cassiopeia-high-in-the-north-on-winter-evenings/)
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*Topic: Encyclopedia › Physical world and mathematics › Astronomy › Stars and galaxies › Constellations, star names, and catalogs › Individual constellations*
*Initially written Sep 17, 2026 · Reviewed: Oct 15, 2026 · Edited: Oct 15, 2026 · Last review: Oct 15, 2026*
*Copyright 2026 EdgeChat AI, a subsidiary of Biostate AI.*
License: Edgepedia Community License 1.0, https://www.edgepedia.org/edgepedia/license