Cepheus
What is Cepheus?
Constellations· Autumn evenings (N) · a house-shaped pentagon beside Cassiopeia. The king of Ethiopia, father of Andromeda, drawn as a house with a pointed roof between Cassiopeia and Polaris. Delta Cephei is the prototype of the Cepheid variables that became the cosmic distance ruler, pulsing every 5.4 days.
📍 Visible from where you are right now — computed in your browser
bearing · altitude · rise time · best time tonight
Where Cepheus is in your sky right now: https://nowsky.org/solar/sky?sel=con:Cepheus — location and time set automatically, no login.
Stars of the figure
| Star | Magnitude |
|---|---|
| Alderamin | 2.5 |
| Alfirk | 3.2 |
| Errai | 3.2 |
| Zeta Cephei | 3.4 |
The 4 brightest of the 6 stars used in the figure (6 lines). Lower magnitude means brighter.
Deep-sky objects near this constellation
Constellation basics
| Season | circumpolar from the north, highest on autumn evenings |
|---|---|
| Brightest star | Alderamin (2.5) |
| How to find | the pointed "house" between Cassiopeia's W and Polaris |
| Area rank | 27th of 88 |
Figures are representative approximations. Source: compiled from NASA and IAU public data.
Frequently asked
- When can I see Cepheus?
- circumpolar from the north, highest on autumn evenings.
- How do I find Cepheus?
- the pointed "house" between Cassiopeia's W and Polaris.
- What is the brightest star in Cepheus?
- Alderamin, magnitude 2.5.
- Where is Cepheus in the sky right now?
- Open the sky view for your location and time and it shows the position in the sky right now.
Herschel's Garnet Star — the reddest star the eye can see
At the southern edge of Cepheus lies Mu Cephei, a 4th-magnitude star so red that William Herschel called it the Garnet Star; through binoculars its colour stands apart from the white stars around it. It is a red supergiant more than 1,000 times the Sun's diameter, and set in the Sun's place it would extend beyond the orbit of Jupiter. Its size is why it can be seen by eye from 3,000 light-years away.
The star varies irregularly between magnitude 3.4 and 5.1 over periods of two to five years. Its loose outer layers pulsate and shed material, and it is counted among the candidates to explode as a supernova one day. Cepheus gave astronomy its yardstick for cosmic distance in Delta Cephei, and within the same constellation sits a vast red star approaching the end of its life.
The constellation in depth
Cepheus was king of Ethiopia, and together with Queen Cassiopeia, daughter Andromeda and son-in-law Perseus he forms a family group in the autumn sky. Lacking bright stars he is easy to overlook, but being close to the pole he never sets from mid-northern latitudes. Ptolemy included Cepheus among his 48 constellations, and its outline has changed little in two thousand years.
Delta Cephei, found to vary by John Goodricke in 1784, is a pulsating star; in 1912 Henrietta Leavitt showed that longer periods mean brighter stars, turning Cepheids into standard candles for measuring galaxies. Hubble used them to prove Andromeda lies beyond the Milky Way. Mu Cephei, Herschel's Garnet Star, is a hypergiant visibly red to the eye, and the Elephant's Trunk Nebula, IC 1396, also lies here.
On autumn evenings look north between Cassiopeia's W and Polaris for five stars arranged like a house with a pointed roof, sometimes upside down. Alderamin marks one lower corner. Compare Delta Cephei with its neighbours Zeta and Epsilon over several nights and you can watch it brighten and fade. Set the Sky view to an October night to find it.
Related
Figures are representative approximations. Simulated positions use J2000 mean elements.