Delta Cephei

Delta Cephei. Image: © T. Credner & S. Kohle, AlltheSky.com

The second Cepheid variable to be identified and the prototype for the category known as Type I Cepheids, or Delta Cephei stars. With a change in apparent magnitude of 3.5 to 4.4 over a period of 5.366 days, Delta Cep's entire range of variability can be followed with the naked eye.

At a declination of +58°, Delta makes a perfect target for northern observers, especially those who see Cepheus as a circumpolar constellation. Also, it lies conveniently between two bright stars that shine close to each end of its range of variability: Zeta Cep (magnitude 3.6) and Epsilon Cep (magnitude 4.2). For those observing with binoculars or a modest telescope, Delta Cep's companion stars can be discerned. A seventh magnitude mate is located 41" from the variable itself and is thought to be physically associated with it. A second nearby star of 13th magnitude, located 20.9" from Delta, is most likely a line-of-sight object.

visual magnitude	4.07 (mean)
absolute magnitude	-3.47
spectral type	G2Ib
temperature	5,500–6,800 K
luminosity	2,000 L_sun
mass	5 M_sun
distance	890 light-years (273 pc)
position	R.A. 22h 29m 12s, Dec. +58° 25' 08"
other designations	27 Cep, HR 8571, BD +57°2548, HD 213306, SAO 34508, FK5 847, AAVSO 2225+57, IRAS 22273+5809, HIP 110991

Related categories

• NOTABLE STARS
• VARIABLE STARS

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