61 Cygni B
Star
61 Cygni B — the fainter, cooler orange dwarf (K7V) of the historic 61 Cygni pair. About 63% of the Sun's mass, it circles its companion on a long, wide orbit of several centuries. Like its twin it is chromospherically active, with starspots and a magnetic cycle.
Open in 3D viewSee 61 Cygni B in the live, interactive 3D map
Key facts
Mutual orbit
678 Earth years
247,640 Earth days
Mass
1.25 × 10³⁰ kg
0.63 M☉
Radius
413,942 km
60% of the Sun's radius
Surface temperature
4,044 K (3,771 °C)
Luminosity
3.25 × 10²⁵ W
Spectral type
K7V (orange dwarf)
Science
Physical
- Mass
- 1.25 × 10³⁰ kg · 0.63 M☉
- Radius
- 413,942 km · 60% of the Sun's radius
- Density
- 4,217 kg/m³ · 4.2× water
- Computed from mass and radius
- Spectral type
- K7V (orange dwarf)
Motion through space
- Note
- The motion of the pair's common centre of mass, computed as the mass-weighted mean of its stars' catalogued motions.
- Proper motion
- 5.23 arcseconds per year · its drift across our sky
- SIMBAD — 2020yCat.1350....0G
- Radial velocity
- -65.1 km/s · approaching the Sun
- SIMBAD — 2020yCat.1350....0G
- Speed across our line of sight
- 86.7 km/s
- Computed from proper motion and parallax
- Speed through space, relative to the Sun
- 108 km/s
- Computed from proper motion, parallax and radial velocity
Orbit (around the system barycenter)
- Semi-major axis
- 44.7 AU
- From the visual-binary orbit (P ≈ 678 yr, a ≈ 85 AU, e ≈ 0.48)
- Eccentricity
- 0.48
- From the visual-binary orbit (P ≈ 678 yr, a ≈ 85 AU, e ≈ 0.48)
- Orbital period
- 678.00 years
- From the visual-binary orbit (P ≈ 678 yr, a ≈ 85 AU, e ≈ 0.48)
Rotation
- Note
- Rotates about once every 38 days.
Composition
- By mass
- A cooler orange dwarf about 63% of the Sun's mass, circling its companion on a centuries-long orbit. Like its twin it is chromospherically active, with spots and a magnetic cycle.
Temperature
- Surface
- 4,044 K (3,771 °C)
Radiation & temperature
- Luminosity
- 3.25 × 10²⁵ W · 0.085 L☉
- Surface temperature
- 4,044 K (3,771 °C)
- Peak wavelength
- 717 nm · red light
- Computed (Wien's law) from the surface temperature
Discovery & history
- Method
- Naked-eye star
- Name
- '61 Cygni B' is the fainter component of 61 Cygni, in Cygnus, the Swan.
Measured together with 61 Cygni A when Bessel determined the system's parallax in 1838 — the first stellar distance ever found. The two stars share the same large proper motion across the sky.
Images
Images from open archives · credit shown per image