# Zosma (Delta Leonis)

Zosma (Delta Leonis) is a star in the constellation Leo, magnitude 2.5.

**A white star on the Lion’s back, spinning so fast that it bulges at the middle.**

Spin a star fast enough and it stops being round. Zosma turns so quickly — about 280 kilometres per second at its equator, well over 100 times the Sun’s rate — that it bulges at the middle. Its polar radius is only about 84% of its equatorial one.

Underneath the spin is a hot white [star](https://astropilot.space/glossary/star) a little over twice the Sun’s width, a size measured directly with an interferometer, and more than 15 times as luminous. Heavier stars live faster: in roughly 600 million years Zosma will swell into an orange or red giant, then fade as a white dwarf of carbon and oxygen.

The name is ancient Greek for “girdle”, for its place on the Lion’s hip. Zosma may also have famous siblings: its path through space suggests it belongs to the Ursa Major Moving Group, a family of stars around 500 million years old that includes most of the Big Dipper.

Zosma (Delta Leonis) is 58 light-years away: the light we see from it set off in 1968, around the time Apollo 11 landed on the Moon.

## Did you know?

- **A minister of state.** In Chinese astronomy Zosma sits in the Right Wall of the Supreme Palace Enclosure, where it represents the First Western Minister — the “Higher Minister of State”.
- **The Lion’s back.** Arabic tradition also called it Dhur or Duhr, from the word for “back” — another name that describes exactly where it sits in the Lion.

A white star of magnitude 2.5 on the Lion’s back, the northern corner of the triangle that forms Leo’s hindquarters with Chertan and Denebola. Start from Regulus and the Sickle, then look east for the triangle.

## When and where to see it

It is best placed in the evening sky around April, when it crosses the meridian at about 10 pm local time (around midnight in March). It can be seen from everywhere north of 69°S and never sets north of 69°N.

At its highest it stands 61° up from 50°N, 76° up from 35°N, 69° up from the equator, 34° up from 35°S.

## Facts

- Type: Star
- Constellation: Leo
- Designations: Delta Leonis, δ Leo, 68 Leo, HR 4357, HD 97603, HIP 54872
- Magnitude: 2.5
- Position: RA 11h 14.1m, Dec +20° 31′ (J2000)
- Spectral type: A5IV(n)
- Colour: yellow-white (B−V 0.15)
- Distance: 58 light-years
- Discovered: Known since antiquity

Open AstroPilot to see when Zosma (Delta Leonis) is highest tonight from your location, how easy it is with your telescope or binoculars, and an eyepiece view. https://astropilot.space/object/zosma