W Sagittarii

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W Sagittarii
Observation data
Epoch J2000.0      Equinox J2000.0
Constellation Sagittarius
Right ascension 18h 05m 01.3s
Declination -29° 34' 48"
Apparent magnitude (V) 4.29 - 5.14[1]
Distance 2000 ± 1200 ly
(600 ± 370 pc)
Spectral type F4-G2Ib[1]
Other designations
W Sagittarii, HR 6742, HD 164975, SAO 186237, HIP 88567, ADS 11029,CCDM 18050-2935

W Sagittarii (W Sgr) is a cepheid variable star in the constellation Sagittarius. It was temporarily referred to as Gamma-1 Sagittarii (γ¹ Sgr). It is an optical line-of-sight companion to the much brighter [Al Nasl] Gamma-2 which marks the "nozzle" ("spout") of the "teapot" asterism forming a large part of Sagittarius.[2]


This variable star changes in apparent magnitude from 4.29m to 5.14m with a period of 7.6 days. Its change in brightness is accompanied by a change in spectral classification, from G2Ib to F4Ib.[1] Based on its variability, W Sagittarii has been estimated to be approximately 1,500 light years from Earth.[2]

Binary system[edit]

W Sagittarii also shows evidence of being a close binary star, as well has having two more distant 13th-magnitude optical companions, W Sagittarii B and C separated by 33 and 48 arcseconds respectively.[2]


  1. ^ a b c Watson, Christopher (4 January 2010). "W Sagittarii". The International Variable Star Index. American Association of Variable Star Observers. Retrieved 28 May 2015. 
  2. ^ a b c Kaler's Stars website - Al Nasl page