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Delta Cephei, 27 Cephei

Delta Cephei Variable (type I Cepheid) in Cepheus

Right Ascension 22 : 29 : 10.2 (h:m:s)
Declination +58 : 24 : 55 (deg:m:s)
Distance 1,340 (ly)
Visual brightness 3.48 .. 4.37 (mag)
Period 5.366 (days)
Spectra type F5Ib - G2Ib

Delta Cephei was discovered by John Goodricke in 1784. It was actually the second Delta Cephei Star, or Cepheid variable, to be discovered; the first one, Eta Aquilae, had been discovered earlier the same year by Goodricke's good friend, neighbor and collaborator Edward Pigott.

Delta Cephei varies with a period of 5.366341 days (or 5 days 8 hours 37.5 minutes) from magnitude 3.48, spectral type F5 in its maximum to mag 4.37, spectral type G2 in its minimum. The star shows a quick and sharp rise from minimum to maximum, and slowly declines to its minimum again. It is a yellow supergiant like all Delta Cephei stars.

Cepheid variables are pulsating stars, which expand and contract at extremely regular periods. For those stars, brightness maxima and hottest surface temperatures occur when their expansion velocity is greatest; this is shortly after the stars, or their outer layers, are most compressed to their minimal radius. Analogously, their minima in temperature and brightness occur when they are in the contraction phase.

Delta Cephei was found to be at about 1300 ly and is approaching us at 17 km/s.

Delta Cephei is an easily separable double star in an amateur telescope; its companion "C" of mag 7.5, spectrum A0 was discovered by F.W.G. Struve in 1835. Another, probably optical (not physically related) companion, "B", of mag 13.0 and at PA 284 deg from the primary, was found by S.W. Burnham in 1878.

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Hartmut Frommert
Christine Kronberg