# Iota¹ Scorpii (ι¹ Sco)

Iota¹ Scorpii (ι¹ Sco) is a star in the constellation Scorpius, magnitude 3.0.

**An ultra-luminous yellow-white supergiant in the Scorpion’s tail, shining like 35,000 Suns through a veil of dust.**

The ‘Ia’ in Iota¹ Scorpii’s [classification](https://astropilot.space/glossary/spectral-type), F2 Ia, puts it in the top tier of stars: a supergiant brighter even than ordinary supergiants. With some 12 solar masses, it shines about 35,000 times as brightly and has swollen to about 120 times the Sun’s radius. Set in the Sun’s place, it would reach well beyond the orbit of Mercury.

Its surface, at around 7,000 kelvins, glows yellow-white, hotter than the Sun’s. And much of its light never reaches us: gas and dust along the way dim it by about two-thirds of a magnitude, so without them it would look nearly twice as bright.

Iota¹ Scorpii (ι¹ Sco) is 1,900 light-years away: the light we see from it set off around AD 130, around the time the Pantheon was rebuilt in Rome.

## Did you know?

- **A distant companion.** A 10th-magnitude companion lies 37.5 arcseconds from Iota¹ Scorpii. At the supergiant’s distance that gap is enormous — and the true separation may be larger still.
- **Top of the class.** Luminosity class Ia is reserved for the most luminous supergiants. The Sun, by comparison, is class V: an ordinary main-sequence dwarf.

A yellow-white 3rd-magnitude star on the curl of the Scorpion’s tail, just south-east of Kappa Scorpii. A small telescope shows its 10th-magnitude companion about 37 arcseconds away.

## 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 south of 50°N and never sets south of 50°S.

At its highest it stands below the horizon from 50°N, 15° up from 35°N, 50° up from the equator, 85° up from 35°S.

## Facts

- Type: Star
- Constellation: Scorpius
- Designations: ι¹ Sco, HR 6615, HD 161471, HIP 87073
- Magnitude: 3.0
- Position: RA 17h 47.6m, Dec −40° 8′ (J2000)
- Spectral type: F2Ia
- Colour: yellow (B−V 0.50)
- Distance: 1,900 light-years
- Discovered: Known since antiquity

Open AstroPilot to see when Iota¹ Scorpii (ι¹ Sco) is highest tonight from your location, how easy it is with your telescope or binoculars, and an eyepiece view. https://astropilot.space/object/iota1-scorpii