Queen Cassiopeia · pronounced Cassiopeia. Cassiopeia, meaning “Queen Cassiopeia,” is an official IAU constellation centred near right ascension 23.6 hours and declination 55.5°. Its northern position determines where and when it is easiest to observe. It belongs to the classical constellation tradition recorded by Ptolemy in the second-century Almagest. Its modern role is different: the IAU constellation is a precisely bounded area of sky, not only the familiar stick figure. The plotted outline is only a recognition aid; every galaxy, nebula and star inside the official boundary belongs to Cassiopeia, even when it is not joined by a line. Observers should begin with a wide-field chart, identify brighter neighbouring patterns, and then compare the field with a red-light atlas. Binoculars reveal denser star fields than the naked eye, while a telescope is needed for most faint deep-sky targets. Because visibility changes with latitude, season and local horizon, the coordinates and boundary chart are more reliable than mythology alone when planning an observing session.
About Cassiopeia
Cassiopeia is one of the 88 constellations recognized by the International Astronomical Union. Its standard three-letter abbreviation is Cas, and astronomers use the genitive form Cassiopeiae when naming stars associated with it. The constellation's reference position lies around right ascension -0.4 hours and declination +56 degrees.
Its location places it in the northern sky. For a typical mid-latitude observer, this part of the celestial sphere is especially well placed during autumn evenings. Exact visibility depends on latitude, local horizon, date and time.
History and mythology of Cassiopeia
Classical origin
It belongs to the classical constellation tradition recorded by Ptolemy in the second-century Almagest. Its modern role is different: the IAU constellation is a precisely bounded area of sky, not only the familiar stick figure.
The modern constellation
In 1922 the International Astronomical Union adopted Cassiopeia among the 88 official constellations. Eugène Delporte’s later boundary work made it a defined region of the celestial sphere, allowing cataloguers to assign objects unambiguously.
How to find Cassiopeia
- Choose a dark site with a clear view toward the northern sky.
- Observe during northern summer and autumn evenings, when the constellation is better placed in the evening.
- Centre a chart near RA 23.6h, Dec 55.5° and identify brighter neighbouring patterns before tracing its official line figure.
- Confirm faint targets with an interactive Aladin or Stellarium view; the IAU boundary extends beyond the connected stars.
Bright stars in Cassiopeia
Schedar
Notable star- Magnitude
- 2.24
- Distance
- about 228 light-years
A documented stellar landmark in Queen Cassiopeia; magnitude is apparent visual brightness and distance is rounded.
Caph
Notable star- Magnitude
- 2.28
- Distance
- about 55 light-years
A documented stellar landmark in Queen Cassiopeia; magnitude is apparent visual brightness and distance is rounded.
Gamma Cassiopeiae
Notable star- Magnitude
- 2.5
- Distance
- about 550 light-years
A documented stellar landmark in Queen Cassiopeia; magnitude is apparent visual brightness and distance is rounded.
Ruchbah
Notable star- Magnitude
- 2.68
- Distance
- about 100 light-years
A documented stellar landmark in Queen Cassiopeia; magnitude is apparent visual brightness and distance is rounded.
Deep-sky objects in Cassiopeia
M52
A well-established open cluster within the official Queen Cassiopeia sky region and a useful target for appropriately sized optics.
M103
A well-established open cluster within the official Queen Cassiopeia sky region and a useful target for appropriately sized optics.
NGC 457
A well-established open cluster within the official Queen Cassiopeia sky region and a useful target for appropriately sized optics.
NGC 7789
A well-established open cluster within the official Queen Cassiopeia sky region and a useful target for appropriately sized optics.
IC 1805 Heart Nebula
A well-established emission nebula within the official Queen Cassiopeia sky region and a useful target for appropriately sized optics.
Interesting facts about Cassiopeia
- Cassiopeia’s traditional name refers to queen cassiopeia, while its official IAU boundary defines a precise region of the sky.
- Schedar, at magnitude 2.24, is a key star in Cassiopeia. A documented stellar landmark in Queen Cassiopeia; magnitude is apparent visual brightness and distance is rounded.
- M52 is a notable open cluster in Cassiopeia. A well-established open cluster within the official Queen Cassiopeia sky region and a useful target for appropriately sized optics.
- M103, a open cluster, is another observing target within the constellation.
- It belongs to the classical constellation tradition recorded by Ptolemy in the second-century Almagest.