User:ST11/68 Cygni

68 Cygni, is a star in the constellation Cygnus.

History
Being visible to the naked eye, 68 Cygni would have been observable since ancient times, but the first known cataloging and designation of the star was by Johann Bayer, who assigned it the Bayer designation A Cygni. Bayer grouped stars into six magnitude groupings (1st- through 6th-magnitude) and assigned Greek letters to the brightest 24 stars in these groupings, sorted by right ascension within groups. When he ran out of Greek letters, Bayer then moved on to Latin letters; thus, 68 Cygni was the 25th star Bayer designated in Cygnus.

The star was later observed by John Flamsteed, who cataloged naked-eye stars by constellation. Contrary to popular belief, Flamsteed did not assign the stars Flamsteed designations; rather, the French astronomer Joseph Jérôme de Lalande assigned Flamsteed numbers to stars in each constellation in order of right ascension. Since this star was the 68th star by right ascention in Cygnus, it was numbered 68 Cygni, the designation by which this star is most commonly-known by today, as most latin-letter Bayer designations are no longer in common use.

Observation
In the night sky, 68 Cygni is located west of the main asterism of Cygnus, slightly south of the midpoint of the imaginary line between the 3rd-magnitude stars Xi Cygni and Rho Cygni. With an apparent magnitude of approximately 5.0, the star cannot be easily seen with the naked eye from polluted areas or with a full moon.

Properties
According to the star's measured parallax of 0.70 milliarcseconds, it is located approximately 1400 pc distant, although such low parallax values are subject to low precision, and thus with the error taken into account, the star could be anywhere from 1080 pc to 2130 pc distant, it is a hot blue giant of spectral type O7.5III:ne. Such hot and massive stars may only spend a few million years on the main sequence (compared to around 10 billion years for sun-like stars) before leaving the main sequence and evolving into blue supergiants or Wolf–Rayet stars. 68 Cygni, as a blue giant, is in this phase of evolution. The colon in the spectral type indicates that there is some uncertainty in the spectral type, the "e" indicates that emission lines are present, and the "n" indicates that that the absorption lines present are wide due to the rapid rotation rate of the star.

The star is surrounded by a ring-shaped nebula.

The star is a rotating ellipsoidal variable, meaning that it is a binary system whose components are distorted into ellipses, causing variations in brightness. 68 Cygni itself varies between magnitudes 4.98 and 5.09, and, as the 1809th star discovered to be variable in Cygnus, was assigned the variable star designation V1809 Cygni in 1984. The secondary component of the system has a mass of approximately three solar masses and an orbital period of 5.1 days.