King Cepheus · pronounced Cepheus. Cepheus, meaning “King Cepheus,” is an official IAU constellation centred near right ascension 22.5 hours and declination 71°. 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 Cepheus, 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 Cepheus
Cepheus is one of the 88 constellations recognized by the International Astronomical Union. Its standard three-letter abbreviation is Cep, and astronomers use the genitive form Cephei when naming stars associated with it. The constellation's reference position lies around right ascension -1.5 hours and declination +71 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 summer evenings. Exact visibility depends on latitude, local horizon, date and time.
History and mythology of Cepheus
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 Cepheus 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 Cepheus
- 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 22.5h, Dec 71° 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 Cepheus
Alderamin
Notable star- Magnitude
- 2.45
- Distance
- about 49 light-years
A documented stellar landmark in King Cepheus; magnitude is apparent visual brightness and distance is rounded.
Errai
Notable star- Magnitude
- 3.21
- Distance
- about 45 light-years
A documented stellar landmark in King Cepheus; magnitude is apparent visual brightness and distance is rounded.
Alfirk
Notable star- Magnitude
- 3.23
- Distance
- about 690 light-years
A documented stellar landmark in King Cepheus; magnitude is apparent visual brightness and distance is rounded.
Delta Cephei
Notable star- Magnitude
- 3.5–4.4
- Distance
- about 887 light-years
A documented stellar landmark in King Cepheus; magnitude is apparent visual brightness and distance is rounded.
Deep-sky objects in Cepheus
NGC 188
A well-established open cluster within the official King Cepheus sky region and a useful target for appropriately sized optics.
IC 1396A Elephant’s Trunk
A well-established dark nebula within the official King Cepheus sky region and a useful target for appropriately sized optics.
NGC 7023 Iris
A well-established reflection nebula within the official King Cepheus sky region and a useful target for appropriately sized optics.
NGC 6946 Fireworks
A well-established spiral galaxy within the official King Cepheus sky region and a useful target for appropriately sized optics.
Interesting facts about Cepheus
- Cepheus’s traditional name refers to king cepheus, while its official IAU boundary defines a precise region of the sky.
- Alderamin, at magnitude 2.45, is a key star in Cepheus. A documented stellar landmark in King Cepheus; magnitude is apparent visual brightness and distance is rounded.
- NGC 188 is a notable open cluster in Cepheus. A well-established open cluster within the official King Cepheus sky region and a useful target for appropriately sized optics.
- IC 1396A Elephant’s Trunk, a dark nebula, is another observing target within the constellation.
- It belongs to the classical constellation tradition recorded by Ptolemy in the second-century Almagest.