Saiph (Kappa Orionis)

Saiph (Kappa Orionis) is a star in the constellation Orion, magnitude 2.1.

Orion’s other foot — a blue supergiant hotter than Rigel, destined to end as a supernova.

Saiph’s name is a case of mistaken identity. It comes from the Arabic saif al-jabbar, “sword of the giant”, a name that first belonged to another of Orion’s stars, Eta Orionis. A 17th-century catalogue gave it a more fitting label: Genu Dextrum Gigantis, the “right knee of the giant”.

It is a blue supergiant star that has already used up the hydrogen in its core. Smaller and less luminous than Rigel but hotter at its surface, it still shines around 57,000 times as brightly as the Sun. Estimates of its mass run from about 15 to 28 Suns, and one study puts its age at just 6.2 million years.

A fierce wind streams off its surface, carrying away the equivalent of the Sun’s entire mass every 1.1 million years. Like many of Orion’s great stars, Saiph is destined to collapse and explode as a supernova.

Saiph (Kappa Orionis) is 650 light-years away: the light we see from it set off around 1375, 80 years before Gutenberg printed his Bible.

Did you know?

• The Python’s digging stick. The Wardaman people of northern Australia see Saiph as the Guman digging stick, used by Black-headed Python to make a canyon.
• Sixth of the Three Stars. In Chinese astronomy Saiph is the Sixth Star of Shēn, the Three Stars — an asterism that also takes in Betelgeuse, Rigel, Bellatrix and the three belt stars.

A blue-white 2nd-magnitude star at Orion’s south-east corner, diagonally opposite Bellatrix. Compare it with Rigel across the bottom of the figure: Saiph looks much fainter, though its surface is hotter.

What is a star?

When and where to see it

It is best placed in the evening sky around January, when it crosses the meridian at about 10 pm local time (around midnight in December). It can be seen from everywhere south of 80°N and never sets south of 80°S.

At its highest it stands 30° up from 50°N, 45° up from 35°N, 80° up from the equator, 65° up from 35°S.

Facts

Type

Star

Constellation

Orion

Designations

Kappa Orionis, κ Ori, 53 Ori, HR 2004, HD 38771, HIP 27366

Magnitude

2.1

Position

RA 5h 47.8m, Dec −9° 40′ (J2000)

Spectral type

B0.5Ia

Colour

blue-white (B−V -0.18)

Distance

650 light-years

Discovered

Known since antiquity

Open AstroPilot to see when Saiph (Kappa Orionis) is highest tonight from your location, how easy it is with your telescope or binoculars, and an eyepiece view.