Star profile
Sigma Cygni
Hot blue starWhat is Sigma Cygni
Sigma Cygni is a blue supergiant almost three thousand light-years away, embedded in the Cygnus OB4 association. Its atmosphere is chemically strange: abnormally rich in helium, nitrogen, calcium, cerium and europium, depleted in carbon and aluminium. Corrected for the light absorbed by interstellar dust, it shines more than fifty thousand times brighter than the Sun. Internal pulsations with a 1.59-hour period stir its spectral lines while leaving its brightness untouched.
Where it is and when to see it
Sigma Cygni lies in the northern celestial hemisphere. It is visible to the naked eye under a dark sky. Its best month of the year is September, when it culminates around midnight.
- From London it never sets and culminates about 78° up.
- From New York it culminates about 89° above the horizon.
- From Sydney it culminates about 17° above the horizon.
It can be seen from anywhere north of 51° S.
It ranks no. 18 in brightness among the 137 stars of Cygnus in our catalogue. To find it, start from Deneb, the brightest: it lies about 9° away (a fist at arm's length covers about 10°).
The light you see today left it about 2,900 years ago.
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Astronomical data for Sigma Cygni
- Constellation
- Cygnus
- Apparent magnitude
- 4.22
- Distance
- 2886.7 light years
- Coordinates (J2000)
- RA 319.354° · Dec 39.395°
- Catalogue
- HIP 105102 · HD 202850
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Other stars in Cygnus
Cygnus has 137 stars in Stelvia's catalogue. Here are a few of them.
- DenebAlpha Cygni1.25
- SadrGamma Cygni2.23
- AljanahEpsilon Cygni2.48
- Rho Cygni3.98
- 41 Cygni4.01
- 52 Cygni4.22
- Pi 2 Cygni4.23
- 33 Cygni4.28