16 Cygni

The orbits of the 16 Cygni system

The orbits of stars in the 16 Cygni system.

location of 16 Cygni B

Figure 1. Location of 16 Cygni.

16 Cygni

Figure 2. The two brighter stars of 16 Cygni.

orbit of 16Cygni B

Figure 3. Orbit of 16 Cyg Bb around 16 Cyg B (HD 186427).

16 Cygni is a triple star system in the constellation Cygnus (Figure 1) consisting of two reasonably Sun-like stars (both yellow dwarfs) and a red dwarf. One of the Sun-like components (16 Cygni B) has been found to have a planet (16 Cygni Bb) with a mass about 1½ times that of Jupiter in a highly elongated orbit (Figure 3). The distance of the planet from 16 Cygni B varies between less than the Venus-Sun distance and more than the Mars-Sun distance.


The two brighter stars in the 16 Cyg system form a visual binary (Figure 2) and are separated by about 860 astronomical units with an orbital period of at least 18,000 years. 16 Cyg A is very similar to the Sun; 16 Cyg B is slightly smaller and dimmer.


The 16 Cygni system, which is much older than our own Solar System (with an age of about 10 billion years), is among those that were investigated by the Kepler mission.


Stars: 16 Cyg A and 16 Cyg B
distance 70.0 light-years (21.15 pc)
spectral type G1.5V (A); G2.5V (B)
apparent magnitude 5.96 (A); 6.20 (B)
metallicity 0.09 (B)
mass 1.01 Msun (B)
position RA 19h 41m 48.9s, Dec 50° 31' 30.2" (A)
RA 19h 41m 52.0s, Dec 50° 31' 3.1" (B)
other designations Gl 765.1A, BD +50 2847, HD 186408, HIP 96895 (A)
Gl 765.1B, BD +50 2848, HD 186427, HIP 96901 (B)


Planet: 16 Cyg B b
mass (Jupiter=1) 1.68
semimajor axis 1.67 AU (251 million km, 155 million mi)
orbital period 798.9 days
eccentricity 0.67
discovery 1997, Marcy et al, California Carnegie Planet Search
method of discovery radial velocity



1. Cochran W., Hatzes A., Butler P., and Marcy G. "The discovery of a planetary companion to 16 Cyg B," Astrophysical Journal, 483, 457 (1997).
2. Hauser, H., and Marcy, G. "The Orbit of 16 Cygni AB," Publications of the Astronomical Society of the Pacific, 111, 321 (1999).
3. Laws C., and Gonzalez, G. "A Differential Spectroscopic Analysis of 16 Cygni A and B," Astrophysical Journal, 553, 405 (2001).