Aljanah (Epsilon Cygni)
Aljanah (Epsilon Cygni) is a star in the constellation Cygnus, magnitude 2.5.
A nine-billion-year-old orange giant — a preview of what the Sun will one day become.
Here is a glimpse of the Sun’s far future. Aljanah is only about 10% heavier than the Sun but roughly twice its age — some nine billion years old — and it has already been through its red-giant phase. A sudden helium flash ignited helium in its core, which it now fuses quietly, swollen to 11 times the Sun’s width and glowing a warm orange.
It does not travel alone. A hidden partner, never seen but given away by a wobble in Aljanah’s spectrum, swings around it every 53 years on a stretched-out orbit, closing to about the Earth–Sun distance and then pulling out about as far as Neptune is from the Sun.
Its name is Arabic for “the wing”: it marks one of the Swan’s outstretched wings. For centuries it was called Gienah, but so was a star in Corvus, so in 2017 the IAU settled on Aljanah, another rendering of the same Arabic word, for this one.
Aljanah (Epsilon Cygni) is 73 light-years away: the light we see from it set off in 1953, 4 years before Sputnik became the first artificial satellite.
Did you know?
- A yardstick star. Since 1943 astronomers have used Aljanah’s spectrum as one of the fixed anchor points against which other stars are classified.
- A distant follower. A 13th-magnitude star 78 arcseconds away shares Aljanah’s motion through space. If the two are bound, a single orbit would take at least 50,000 years.
- Ninth star of the Celestial Ford. Chinese astronomers made it the ninth star of Tiān Jīn, the Celestial Ford, a chain of nine stars strung across Cygnus.
An orange star of magnitude 2.5 marking the eastern wing of Cygnus, the Northern Cross; its warm tint is easy to compare with white Deneb. The Veil Nebula lies about three degrees to its south — sweep there with a nebula filter.
When and where to see it
It is best placed in the evening sky around September, when it crosses the meridian at about 10 pm local time (around midnight in August). It can be seen from everywhere north of 56°S and never sets north of 56°N.
At its highest it stands 74° up from 50°N, 89° up from 35°N, 56° up from the equator, 21° up from 35°S.
Facts
- Type
- Star
- Constellation
- Cygnus
- Designations
- Epsilon Cygni, ε Cyg, 53 Cyg, HR 7949, HD 197989, HIP 102488
- Magnitude
- 2.5
- Position
- RA 20h 46.2m, Dec +33° 58′ (J2000)
- Spectral type
- K0III
- Colour
- orange (B−V 1.04)
- Distance
- 73 light-years
- Discovered
- Known since antiquity
Open AstroPilot to see when Aljanah (Epsilon Cygni) is highest tonight from your location, how easy it is with your telescope or binoculars, and an eyepiece view.