Cebalrai (Beta Ophiuchi)
Cebalrai (Beta Ophiuchi) is a star in the constellation Ophiuchus, magnitude 2.8.
The shepherd’s dog — an orange giant younger than the Sun.
Cebalrai is younger than the Sun — about 2.75 billion years old, 60% of the Sun’s age — yet it is already a giant. Stars with more mass race through their lives, and this one has used up its core hydrogen and swollen to about 12 times the Sun’s width, shining 58 times as brightly from a cool orange surface near 4,560 K.
It is gently restless. Its surface probably moves in and out on a 142-day rhythm, picked up as a shifting speed in its spectrum, and its brightness changes by just two hundredths of a magnitude.
Its name comes from the Arabic kalb al-rā‘ī, “the shepherd’s dog”, the source too of variants such as Cheleb and Kelb Alrai.
Cebalrai (Beta Ophiuchi) is 82 light-years away: the light we see from it set off in 1944, 13 years before Sputnik became the first artificial satellite.
Did you know?
- USS Cheleb. The US Navy named a Crater-class cargo ship after the star, using one of its other names: USS Cheleb (AK-138).
- A calm orbit. Cebalrai belongs to the galaxy’s thin disc. It follows a nearly circular path around the Milky Way that never takes it far from the galaxy’s midplane.
An orange star of magnitude 2.8 on the Serpent-bearer’s shoulder, bright enough to see even from town. Rasalhague, the head of Ophiuchus, lies about 8 degrees to the north-north-west; compare Cebalrai’s orange with its white.
When and where to see it
It is best placed in the evening sky around July, when it crosses the meridian at about 10 pm local time (around midnight in June). It can be seen from everywhere north of 85°S and never sets north of 85°N.
At its highest it stands 45° up from 50°N, 60° up from 35°N, 85° up from the equator, 50° up from 35°S.
Facts
- Type
- Star
- Constellation
- Ophiuchus
- Designations
- Beta Ophiuchi, β Oph, 60 Oph, HR 6603, HD 161096, HIP 86742
- Magnitude
- 2.8
- Position
- RA 17h 43.5m, Dec +4° 34′ (J2000)
- Spectral type
- K2IIICN0.5
- Colour
- orange (B−V 1.18)
- Distance
- 82 light-years
- Discovered
- Known since antiquity
Open AstroPilot to see when Cebalrai (Beta Ophiuchi) is highest tonight from your location, how easy it is with your telescope or binoculars, and an eyepiece view.