HD 187123

HD 187123

HD 187123 is a star almost identical to the Sun, in the constellation Cygnus, around which has been discovered a planet with at least half the mass of Jupiter. At one ninth the average separation distance of Mercury from the Sun, HD 187123 b orbits more closely to its host star than any other planet discovered up to that time.1 See also exoplanets.


Host star
Distance 156.3 light-years (47.92 pc)
Spectral type G5V
Apparent magnitude 7.89
Temperature 5,560°C
Luminosity (Sun=1) 1.35
Mass (Sun=1) 1.0
Position R.A. 19h 46m 58.11s; Dec. +34° 25' 10.29"
Other catalog designations BD+34°3708, HIP 97336, SAO 68845


Mass (Jupiter=1) > 0.52
Semi-major axis 0.042 AU (6.3 million km, 3.9 million miles)
Orbital period 3.097 days
Eccentricity 0.03 ± 0.003
Discovery 1998, Butler et al., SFSU Planet Search, Keck
Method radial velocity



1. Butler, P., Marcy, G., Vogt, S., and Apps, K. "A Planet with a 3.1-day Period Around a Solar Twin," Publications of the Astronomical Society of the Pacific, 110, 1389 (1998).