Zeta Ophiuchi (Saik)
Zeta Ophiuchi (Saik) is a star in the constellation Ophiuchus, magnitude 2.6.
The nearest O-type star — a runaway star pushing a glowing wave through the dust.
A runaway star is ploughing through the dust of Ophiuchus, and it leaves a wake. Zeta Ophiuchi moves so fast that it heaps up a glowing arc ahead of it — a bow shock, like the wave at a ship’s prow — captured in infrared by NASA’s WISE telescope.
Why is it running? It may once have had a partner, a heavier star that exploded as a supernova and set it loose. A pulsar, PSR B1929+10, could be that star’s collapsed core: it was flung out of the same family of young stars, on a matching track.
It is the nearest O-type star to the Sun: more than 20 times the Sun’s mass, around 34,000 K at the surface, and spinning perhaps once a day — close to the speed that would tear it apart. Within a few million years it will balloon into a red supergiant wider than Jupiter’s orbit, then explode in turn.
Zeta Ophiuchi (Saik) is 370 light-years away: the light we see from it set off around 1655, 30 years before Isaac Newton published his laws of motion and gravity.
Did you know?
- Hidden by dust. Dust soaks up much of its light. Without it, Zeta Ophiuchi would shine at magnitude 1.5 — the brightest star in Ophiuchus and the 23rd-brightest in the whole night sky.
- Hot poles, cooler waist. Its fast spin stretches the star, so its surface runs from about 39,000 K at the poles to 30,700 K at the equator.
- Moving bumps. In 1979 astronomers spotted bumps travelling across the helium lines in its spectrum, probably caused by the star pulsating. Stars that show them are now called Zeta Ophiuchi stars.
- Hidden by an asteroid. In April 2010 the asteroid 824 Anastasia passed in front of the star in an occultation, briefly hiding it from observers along the asteroid’s shadow path.
A white star of magnitude 2.6, about 16 degrees due north of Antares. It is really one of the hottest stars you can see: dust between us dims it and strips away some of its blue, so it looks whiter and fainter than it should.
When and where to see it
It is best placed in the evening sky around June, when it crosses the meridian at about 10 pm local time (around midnight in June). It can be seen from everywhere south of 79°N and never sets south of 79°S.
At its highest it stands 29° up from 50°N, 44° up from 35°N, 79° up from the equator, 66° up from 35°S.
Facts
- Type
- Star
- Constellation
- Ophiuchus
- Designations
- Saik, ζ Oph, 13 Oph, HR 6175, HD 149757, HIP 81377
- Magnitude
- 2.6
- Position
- RA 16h 37.2m, Dec −10° 34′ (J2000)
- Spectral type
- O9.2IVnn
- Colour
- white (B−V 0.02)
- Distance
- 370 light-years
- Discovered
- Known since antiquity
Open AstroPilot to see when Zeta Ophiuchi (Saik) is highest tonight from your location, how easy it is with your telescope or binoculars, and an eyepiece view.