Cassiopeia A — one of the youngest known supernova remnants in the Milky Way. The star exploded around 1680 CE, about 11,000 light-years away. Image credit: NASA, ESA, and the Hubble Heritage (STScI/AURA)–ESA/Hubble Collaboration.
The W that never sets
In Greek mythology, Cassiopeia was an Ethiopian queen, wife of Cepheus and mother of Andromeda. Her vanity — she boasted she was more beautiful than the sea nymphs — earned her a place in the sky, but a humbling one: she circles the celestial pole and is sometimes depicted upside-down, perpetually tumbling around the sky as punishment.
In practice, Cassiopeia is simply one of the easiest constellations to find. Its five main stars form a clear W (or M, depending on orientation) and are circumpolar from most of the Northern Hemisphere — meaning they never set below the horizon. On autumn and winter evenings in the northern United States, Cassiopeia rides high overhead and can be spotted in seconds from even a suburban backyard.
Cassiopeia is perhaps the most reliably found constellation in the northern sky. If you can draw a W, you can find it.
Cassiopeia at a glance
Abbreviation
Cas · Genitive: Cassiopeiae
Brightest Star
Schedar (α Cas), magnitude 2.24
Size
598 sq. degrees — 25th largest of 88 constellations
Best Visibility
Circumpolar above ~20°N; highest in autumn
Key Stars
- α Cas — Schedar. Magnitude 2.24 (variable). An orange giant ~228 light-years away. The brightest star in the constellation and the bottom-right of the W as it rises.
- β Cas — Caph. Magnitude 2.27. A white giant ~54 light-years away. One of the three stars that share the meridian with the vernal equinox — making it historically useful for timekeeping.
- γ Cas — Navi. Magnitude variable (1.6–3.0). The central star of the W. A hot blue Be star with a circumstellar disk — its brightness fluctuates unpredictably as the disk grows and shrinks. Named "Navi" by astronaut Gus Grissom (his middle name reversed) for use in Apollo spacecraft navigation training.
- δ Cas — Ruchbah. Magnitude 2.66. An eclipsing binary ~99 light-years away. The fourth point of the W.
- ε Cas — Segin. Magnitude 3.35. A blue-white giant at the fifth point of the W, completing the familiar shape.
A star's violent end, still expanding
The single most spectacular object associated with Cassiopeia is Cassiopeia A (Cas A) — the remnant of a supernova explosion roughly 340 years ago, making it one of the youngest known supernova remnants in the Milky Way (only the radio-discovered remnant G1.9+0.3, identified in 2008, is younger). The progenitor star likely exploded around 1680 CE, though it apparently left no strong historical record of a bright new star — possibly because interstellar dust dimmed it.
Cas A sits about 11,000 light-years from Earth in the direction of Cassiopeia. The expanding shock wave now spans roughly 10 light-years and travels at about 6,000 km/s. At X-ray and radio wavelengths, it is the brightest source in the sky outside the solar system. In visible light, Hubble revealed intricate filaments of glowing gas — the shredded outer layers of the progenitor star, colliding with surrounding interstellar material and heating it to millions of degrees.
In 2023 and 2024, the James Webb Space Telescope delivered stunning new infrared views of Cas A — including a mysterious feature dubbed the "Green Monster" — that revealed details of dust and ejecta structure Hubble could not penetrate. (Those images are available at the STScI Webb release page.)
One supernova remnant, every wavelength
The Region Around Cas A
A Digitized Sky Survey view spanning nearly three degrees around the remnant — Cas A itself is a faint wisp embedded in Cassiopeia's dense Milky Way star fields.
Star Field Context
A wide-field infrared view of the rich star fields of Cassiopeia and Cepheus — the constellation lies along the densest portion of the visible Milky Way in the northern sky.
Full Hubble Composite
The 2006 Hubble Heritage color composite reveals the full network of ejecta filaments and shock-heated gas across the supernova remnant.
Hubble Heritage — Color Composite
The classic 2006 Hubble Heritage color composite of Cassiopeia A — one of the most-published Hubble images of any supernova remnant, with the full network of ejecta filaments and shock-heated gas visible.
The Double Cluster (NGC 869 & NGC 884)
Just over the border into Perseus — but best found by sweeping from Cassiopeia — is the Double Cluster, one of the finest naked-eye objects in the sky. Two open clusters separated by just half a degree, each containing hundreds of young, hot stars around 7,500 light-years away.
They are genuinely young clusters: modern estimates put NGC 869 and NGC 884 both at roughly 13 million years old — young siblings of essentially the same age. In binoculars they look like two sparkling clouds side by side. In a small telescope they are breathtaking — easily my favorite naked-eye target in this region.
Star factories along the Perseus arm
Cassiopeia lies along a dense spiral arm of the Milky Way, putting it in line of sight with vast clouds of hydrogen gas where new stars are forming. The result: some of the most photogenic emission nebulae in the northern sky.
Heart Nebula — IC 1805
A massive emission nebula spanning more than 200 light-years, about 7,500 light-years away. Its heart-shaped form is sculpted by the radiation and winds of the young open cluster Melotte 15 at its center.
Soul Nebula — IC 1848
The Soul Nebula is the close companion of the Heart Nebula. Together they form one of the most photographed pairs in the northern sky and an active star-forming region with several embedded young clusters.
Pacman Nebula — NGC 281
About 9,200 light-years away, NGC 281 earned its nickname from the dark dust lane that gives it the unmistakable shape of the arcade-game character. Bok globules dot its inner edge.
Bubble Nebula — NGC 7635
A near-perfect spherical shell of gas seven light-years across, inflated by the fierce stellar wind of a single massive young star visible inside the bubble. Hubble's 2016 image is one of the most stunning of any Cassiopeia object.
Caroline's Rose — NGC 7789
Discovered by Caroline Herschel in 1783, NGC 7789 is one of the richest open clusters in the northern sky — 1.6 billion years old and containing about 1,000 stars arranged in loops that suggest a flower's petals.
Owl / ET Cluster — NGC 457
An open cluster with two bright stars forming "eyes" and chains of fainter stars spreading like wings or arms. Depending on orientation it looks like an owl, or — famously — like the movie character E.T. About 7,900 light-years away.
Messier objects in Cassiopeia
Cassiopeia hosts two Messier catalog objects, both open clusters — easy targets for binoculars and small telescopes.
M52 — NGC 7654
A rich open cluster of about 200 stars, roughly 5,000 light-years away. Easy in binoculars, it appears as a fuzzy star to the naked eye.
M103 — NGC 581
A compact open cluster of about 40 stars, one of the most distant Messier objects at roughly 8,500 light-years. A distinctive reddish giant sits near the center.
The supernovae that changed astronomy
Cassiopeia has hosted two historically significant supernovae. The first, in 1572, blazed bright enough to be seen in daylight. Tycho Brahe's careful observations of SN 1572 — published in De Nova Stella in 1573 — demonstrated it was not a comet or atmospheric phenomenon but a genuine new star far beyond the Moon. That work helped break the Aristotelian doctrine of an unchanging celestial sphere, opening the door to modern observational astronomy.
Its remnant, Tycho's Supernova Remnant, is still visible at radio and X-ray wavelengths today, expanding outward at roughly 9,000 km/s.
The second, around 1680 CE, produced Cassiopeia A. Its relative obscurity in historical records has been attributed to interstellar dust absorption that may have dimmed the visible light significantly even at its peak.
Cassiopeia deep-sky objects
| Object | Type | Distance | Notes |
|---|---|---|---|
| Cassiopeia A | Supernova remnant | ~11,000 ly | Youngest known SNR in Milky Way; brightest radio/X-ray source |
| Tycho's SNR (SN 1572) | Supernova remnant | ~8,000–10,000 ly | Visible only at radio/X-ray; historically pivotal |
| Double Cluster (NGC 869/884) | Open clusters | ~7,500 ly | Naked-eye, spectacular in binoculars |
| M52 (NGC 7654) | Open cluster | ~5,000 ly | Rich and compact; easy binocular object |
| M103 (NGC 581) | Open cluster | ~8,500 ly | Small, triangular; reddish star near center |
| Heart Nebula (IC 1805) | Emission nebula | ~7,500 ly | Large H-alpha emission region |
| Soul Nebula (IC 1848) | Emission nebula | ~6,500 ly | Companion to Heart Nebula |
| Pacman Nebula (NGC 281) | Emission nebula | ~9,200 ly | Distinctive dark dust lane; Bok globules |
| Bubble Nebula (NGC 7635) | Emission nebula | ~7,100 ly | Stellar-wind bubble around BD+60 2522 |
| Caroline's Rose (NGC 7789) | Open cluster | ~7,600 ly | 1.6 billion years old; rich loops of stars |
| NGC 457 | Open cluster | ~7,900 ly | "Owl Cluster" or "ET Cluster"; distinctive shape |
The constellation in the Milky Way
Wide-Field View
A wide-field infrared (WISE) image of the region around Cassiopeia's W, embedded in the rich star fields of the Perseus arm of the Milky Way.
Star Formation Detail
An infrared view of the Soul Nebula's star-forming complex, where young hot stars heat the surrounding gas clouds — typical of what is happening throughout the constellation's nebulae.
Dense Star Fields
Cassiopeia lies along the densest portion of the visible Milky Way north of Cygnus. Every deep exposure in this region shows thousands of resolved stars.
Finding and observing Cassiopeia
Cassiopeia is circumpolar for observers north of about 20°N latitude, meaning it never sets. From the northern United States and Canada, it is visible every clear night of the year. The best approach to finding it:
- Find the Big Dipper. It is recognizable in the northern sky most evenings.
- Draw a line through the two end stars of the handle outward past Polaris.
- Cassiopeia is on the opposite side of the pole from the Dipper, roughly equidistant from Polaris.
In autumn evenings, Cassiopeia is nearly overhead. In spring, it sits lower in the north while the Big Dipper is high. Either way, the W shape is unmistakable once you have seen it.
Naked eye: The W, Cas A region (general direction), Double Cluster (with averted vision).
50mm binoculars: The Double Cluster, M52, M103, NGC 457, M-shape detail.
6-inch telescope: Dozens of open clusters resolve well; M52 and the Double Cluster are showpieces.
Astrophotography target: Heart, Soul, Pacman, and Bubble Nebulae shine in narrowband H-alpha imaging.
New to stargazing? See how to observe the night sky, and if you're choosing gear, the no-hype telescope buying guide.
Constellation data sheet
| Abbreviation | Cas |
| Genitive | Cassiopeiae |
| Right Ascension | 23h 25m (center) |
| Declination | +62° (center) |
| Area | 598 sq. degrees (25th largest) |
| Stars above magnitude 6.5 | ~90 |
| Brightest star | Schedar (alpha Cas), mag 2.24 |
| Bordering constellations | Cepheus, Perseus, Andromeda, Lacerta, Camelopardalis |
| Best visibility | Circumpolar from >20N; highest in autumn evenings |
| Mythology | Ethiopian queen; wife of Cepheus, mother of Andromeda |
Sources & Image Credits
Hubble Space Telescope and ESO ground-based images used under open science and education licenses:
- ESA/Hubble — Cassiopeia A (heic0609a)
- ESA/Hubble — Cas A detail (heic0609b)
- ESA/Hubble — Bubble Nebula (heic1608a)
- NASA/WISE — Pacman Nebula (PIA14873)
- NOIRLab — Messier 52 (noao-m52)
- ESA/Hubble & DSS2 — Cassiopeia A region (heic0609b)
- Wikimedia Commons — Double Cluster, NGC 7789, NGC 457 (see images/credits-additions.md)
- NASA/WISE — Soul Nebula (PIA13014)
- NOIRLab — Heart Nebula (noao-ic1805)
- NOIRLab — Messier 103 (noao-m103)
- NASA/WISE — Cassiopeia–Cepheus wide field (PIA15256); Tycho SNR (PIA13119)
- NASA/CXC — Chandra X-ray Observatory supernova remnants gallery
- NASA/STScI — JWST MIRI Cas A (2023)
- NASA/STScI — JWST NIRCam Cas A (2024)
- Tycho Brahe, De Nova Stella (1573)
- IAU/Sky & Telescope constellation boundaries
Cassiopeia is the queen who never sets — a bright W stitched permanently into the northern night, marking the place where a star once died and still, three centuries on, glows quietly as both a warning and a wonder.
Part of the Royal Family
Cassiopeia opens the connected autumn saga of the Royal Family, mapped on the Greek mythology hub. Her boast sets the whole story in motion.
Cassiopeia · Cepheus · Andromeda · Perseus · Pegasus · Cetus
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