Ascella (Zeta Sagittarii)

Ascella (Zeta Sagittarii) is a star in the constellation Sagittarius, magnitude 2.6.

Three stars in the Teapot’s handle — two of them twins that may one day merge.

The Teapot’s handle hides a family of three. Ascella’s two main stars are near-twins, each almost twice the Sun’s mass, whirling around each other about once a month — closer together than Mercury is to the Sun. A third, heavier star circles the pair every 21 years, making it a triple system.

Their future could be dramatic. In about 500 million years the twins will swell into giants and end up sharing a single envelope of gas. They may then merge into one white dwarf, or settle down as a tight pair of them.

Ascella is Late Latin for “armpit”. Data from the Hipparcos satellite once suggested that about 1.2 million years ago it passed close enough to be the brightest star in Earth’s sky, but a 2023 study found its closest approach was much more distant.

Ascella (Zeta Sagittarii) is 88 light-years away: the light we see from it set off in 1938, 8 years after Pluto was discovered.

Did you know?

• The third returning ostrich. In the Calendarium of Al Achsasi al Mouakket the star was Thalath al Sadirah — “the third returning ostrich”.
• First star of the Dipper. Chinese astronomers made it the first star of Dǒu, the Dipper — a group of six stars, five of which also belong to the Teapot.

A white star of magnitude 2.6 at the southern corner of the Teapot’s handle in Sagittarius. The globular cluster M 54 lies less than 2 degrees to its west — an easy first hop with a telescope.

What is a star?

When and where to see it

It is best placed in the evening sky around August, when it crosses the meridian at about 10 pm local time (around midnight in July). It can be seen from everywhere south of 60°N and never sets south of 60°S.

At its highest it stands 10° up from 50°N, 25° up from 35°N, 60° up from the equator, 85° up from 35°S.

Facts

Type

Star

Constellation

Sagittarius

Designations

Zeta Sagittarii, ζ Sgr, 38 Sgr, HR 7194, HD 176687, HIP 93506

Magnitude

2.6

Position

RA 19h 2.6m, Dec −29° 53′ (J2000)

Spectral type

A2.5Va

Colour

white (B−V 0.10)

Distance

88 light-years

Discovered

Known since antiquity

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