IAU Constellation (Cas) · Genitive: Cassiopeiae · Northern Sky

Cassiopeia Constellation Guide & Objects

Cassiopeia IAU constellation guide: W-shaped circumpolar asterism in the northern Milky Way, hosting Cassiopeia A and pointing to the Double Cluster.

Solid-Angle Area598 sq deg (Rank #25 of 88)
Best Evening MonthNovember
Visibility Latitudes+90° to −20°
Brightest StarSchedar (Alpha Cassiopeiae) (+2.24)

Sky Navigation & Astrophysical Context

Cassiopeia sits directly opposite the Big Dipper across the North Celestial Pole, spanning 598 square degrees of rich Perseus-arm Milky Way star fields. Its five brightest second- and third-magnitude stars—Segin, Ruchbah, Gamma Cassiopeiae, Schedar, and Caph—form the unmistakable 'W' (or 'M') asterism visible all year from latitudes north of +35°.

West of Caph (Beta Cassiopeiae) lies Cassiopeia A, the ~350-year-old core-collapse supernova remnant that shines as the brightest extrasolar radio source in the sky above 1 GHz and a flagship X-ray nucleosynthesis benchmark.

On the eastern side of the W, a line drawn from Gamma Cassiopeiae through Ruchbah (Delta Cassiopeiae) points directly across the Perseus border to the Double Cluster (NGC 869 and NGC 884), while the sharper right-hand V of the W points south toward the Andromeda Galaxy (M31).

Bordering IAU Constellations: Camelopardalis, Cepheus, Lacerta, Andromeda, Perseus.

Equatorial Center Position & Transit Altitude

Cassiopeia is centered near Right Ascension 01h 00m 00s, Declination +60° 00′ 00″ (Cassiopeia (Queen of Aethiopia)).

J2000 Equatorial Sky Position (Cassiopeia) +90° 0° −90° 24h 12h RA 0h Peak Meridian Altitude 70° 40°N Lat 0° 30°S Lat RA: 01h 00m 00s Dec: +60° 00′ 00″ Epoch: J2000.0 · 598 sq deg (Rank #25) First-party vector diagram derived from IAU / CDS SIMBAD / Gaia DR3 astrometry.

Practical Star-Hopping & Observing Tips

  • Use the W of Cassiopeia as a northern sky pointer when the Big Dipper is low on the northern horizon in autumn.
  • Follow the line from Gamma through Delta Cassiopeiae (Ruchbah) 8° southeast to sweep up the Double Cluster in binoculars.
  • Use the sharper V of the W (Segin–Ruchbah–Gamma) as an arrowhead pointing 15° south toward Nu Andromedae and M31.

Notable Celestial Objects in & Near Cassiopeia

Cataloged Stars and Deep-Sky Objects Associated with Cassiopeia
ObjectFamilyClassificationRA (J2000)Dec (J2000)Min. Instrument
Cassiopeia A (3C 461 Young Supernova Remnant)supernova-remnantsYoung core-collapse (Type IIb) supernova remnant & brightest extrasolar radio source23h 23m 26.00s+58° 48′ 54.0″350–450 mm (14–18 inch) telescope under pristine dark skies (primarily an X-ray/IR/radio & imaging target)
Double Cluster (NGC 869 & NGC 884)open-clustersTwin young supergiant open clusters (Perseus OB1 core)02h 20m 00.00s+57° 08′ 00.0″Naked eye; best in binoculars and wide-field telescopes
Delta Cephei (Cepheid Distance Ladder Anchor)variable-starsPrototype Classical Cepheid pulsating supergiant variable22h 29m 10.27s+58° 24′ 54.7″Naked eye for variable light curve; 50 mm telescope for 41″ companion
Messier 52 (NGC 7654 Salt-and-Pepper Cluster)open-clustersYoung rich open star cluster23h 24m 16.00s+61° 35′ 36.0″10×50 binoculars
Owl Cluster (NGC 457 / ET Cluster)open-clustersYoung supergiant open star cluster01h 19m 35.00s+58° 17′ 27.0″7×50 binoculars; delightful in any small telescope
Heart Nebula (IC 1805 / Melotte 15)nebulaeGiant H II emission superbubble and OB open cluster02h 32m 42.00s+61° 27′ 00.0″10×50 binoculars (cluster); 100 mm+ scope + UHC/O-III filter (IC 1795 knot)
Soul Nebula (IC 1848 / Westerhout 5)nebulaeDual-cavity H II emission region and embedded OB cluster02h 51m 18.00s+60° 26′ 00.0″10×50 binoculars (cluster); 100 mm+ scope + UHC/O-III filter (nebula)
Bubble Nebula (NGC 7635 in Cassiopeia)nebulaeO-star stellar-wind bubble embedded in H II region Sh2-16223h 20m 48.00s+61° 12′ 06.0″130–150 mm telescope + UHC/O-III filter (250 mm+ for bubble arc)
Tycho's Supernova Remnant (SN 1572 / 3C 10)supernova-remnantsYoung shell-type Type Ia thermonuclear supernova remnant00h 25m 18.00s+64° 08′ 24.0″CCD/CMOS H-alpha camera (visual star-field landmark in 100 mm+ scopes)
Achird (Eta Cassiopeiae Nearby Solar Binary)multiple-starsNearby visual binary of a solar-analog G0 V dwarf and a K7 V orange-red dwarf00h 49m 06.29s+57° 48′ 54.7″Naked eye; any 50–60 mm telescope at 60×+ splits the 13.5″ color pair

Scientific Sources Cited