Epsilon Capricorni

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"Kastra" redirects here. For the Late Roman fortified camp, see Castra ad Fluvio Frigido.
ε Capricorni A/B
Observation data
Epoch J2000.0      Equinox J2000.0
Constellation Capricornus
Right ascension 21h37m04.8s
Declination −19°27′58″
Apparent magnitude (V) +4.51/+9.5
Distance 660 ± 120 ly
(203 ± 38 pc)
Spectral type B2.5Vpe/K1III-IV
Other designations
Kastra, 39 Capricorni, HR 8260, HD 205637, BD−20°6251/BD−20°6253, FK5 3724, HIP 106723, SAO 164520, GC 30252, BDS 11077, CCDM J21371-1928
Database references

Epsilon Capricorni (ε Cap, ε Capricorni) is a triple star system in the constellation Capricornus. It also has the traditional star name Castra or Kastra, meaning "fort" or "military camp" in Latin. It is approximately 660 light years from Earth.

In Chinese, 壘壁陣 (Lěi Bì Zhèn), meaning Line of Ramparts, refers to an asterism consisting of ε Capricorni, κ Capricorni, γ Capricorni, δ Capricorni, ι Aquarii, σ Aquarii, λ Aquarii, φ Aquarii, 27 Piscium, 29 Piscium, 33 Piscium and 30 Piscium.[1] Consequently, ε Capricorni itself is known as 壘壁陣二 (Lěi Bì Zhèn èr, English: the Second Star of Line of Ramparts.)[2]

The primary component, ε Capricorni A, is a blue-white B-type main sequence dwarf with a mean apparent magnitude of +4.51. It is classified as a Gamma Cassiopeiae type variable star and its brightness varies from magnitude +4.48 to +4.72. It is a spectroscopic binary, and the two subcomponents have apparent magnitudes of +5.0 and +6.3 and are separated by 0.0047 arcseconds (1 AU).

Further out, 68 arcseconds away, is ε Capricorni B which is at least 13,000 AU, or 0.22 light years away from the close binary. It is an orange K-type giant with an apparent magnitude of +9.5.


  1. ^ (Chinese) 中國星座神話, written by 陳久金. Published by 台灣書房出版有限公司, 2005, ISBN 978-986-7332-25-7.
  2. ^ (Chinese) AEEA (Activities of Exhibition and Education in Astronomy) 天文教育資訊網 2006 年 7 月 7 日