Eta Geminorum

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For the AMD Propus processor core, see Athlon II.
Eta Geminorum A/B
Observation data
Epoch J2000.0      Equinox J2000.0 (ICRS)
Constellation Gemini
Right ascension 06h 14m 52.657 / 52.567s
Declination +22° 30′ 24.48 / 24.51″
Apparent magnitude (V) 3.15 to 3.9 / 8.8
Absolute magnitude (V) -2.0 to -1.2 / 3.6
Distance 350±70 ly
(110±20 pc)
Spectral type M3IIIab / G0
Other designations
Propus, Praepes, Tejat Prior, Pish Pai, η Geminorum, η Gem, 7 Geminorum, 7 Gem, HD 42995, HR 2216, BD+22°1241, HIP 29655, SAO 78135, CCDM J06149+2230A/B, ADS 4841A/B
Data sources:
Hipparcos Catalogue,
CCDM (2002),
GCVS (4.2)

Eta Geminorum (η Gem, η Geminorum) is a triple star system in the constellation Gemini. It has the traditional names Tejat Prior, Propus (from the Greek, meaning forward foot) and Praepes and Pish Pai (from the Persian Pīshpāy, پیش‌پای, meaning foreleg).[1]

This star, along with γ Gem (Alhena), μ Gem (Tejat Posterior), ν Gem and ξ Gem (Alzirr) were Al Han'ah, "the brand" (on the neck of the camel). They also were associated in Al Nuḥātai, the dual form of Al Nuḥāt, "a Camel's Hump".[2]

In Chinese lunar mansion, Tejat Prior is the only member of the lunar mansion 钺 (Pinyin: Yuè, Chinese "Battle Axe").[3][4]


Eta Geminorum A is a spectroscopic binary. The primary is a semiregular variable star of type SRA whose brightness changes with a period of 234 days between magnitude +3.15 and +3.9. It is located 350 light years from the Sun and is a red giant of the spectral type M3. The secondary, probably a class B, orbits with a period of 8.2 years. Eta Geminorum B, a class G dwarf, orbits the pair with a period of at least 700 years.[5],[6]

Eta Geminorum is near the ecliptic, so it can be occulted by the Moon and, very rarely, by planets. The last occultation by a planet took place on July 27, 1910, by Venus, and the next to last on July 11, 1837, by Mercury.


USS Propus (AK-132) was a United States Navy Crater class cargo ship named after the star.


  1. ^ p. 235, Star-names and Their Meanings, Richard Hinckley Allen, G. E. Stechert, 1899.
  2. ^ Allen, R. H. (1963). Star Names: Their Lore and Meaning (Reprint ed.). New York, NY: Dover Publications Inc. p. 234. ISBN 0-486-21079-0. Retrieved 2010-12-12. 
  3. ^ (Chinese) AEEA (Activities of Exhibition and Education in Astronomy) 天文教育資訊網 2006 年 5 月 26 日
  4. ^ Richard Hinckley Allen: Star Names — Their Lore and Meaning: Gemini
  5. ^ The Spectrographic Orbit and Light-Variations of η Geminorum, Dean B. McLaughlin and Suzanne E. A. van Dijke, Astrophysical Journal 100 (July 1944), pp. 63–68.
  6. ^ Eta Geminorum at Jim Kaler's STARS.