# Atria (Alpha Trianguli Australis)

Atria (Alpha Trianguli Australis) is a star in the constellation Triangulum Australe, magnitude 1.9.

**The bright corner of the Southern Triangle — an orange giant that would reach almost to Venus.**

Placed where the Sun is, Atria would reach to, or almost to, the orbit of Venus: it is about 139 times the Sun’s width. Born only about 48 million years ago with some 6.4 times the Sun’s mass, it has already left the main sequence and swollen into an [orange](https://astropilot.space/glossary/star-colour) giant — or perhaps a supergiant, as astronomers disagree. It shines with about 4,600 times the Sun’s light from a surface at around 4,600 K.

It also behaves oddly for such a star, flaring and giving off more X-rays than expected. A hidden companion may explain it: a young, magnetically active, Sun-like star circling Atria every 130 years or more.

Its name is simply a contraction of its catalogue label, Alpha Trianguli Australis.

Atria (Alpha Trianguli Australis) is 390 light-years away: the light we see from it set off around 1635, 25 years after Galileo first turned a telescope to the sky.

## Did you know?

- **On Brazil’s flag.** Atria appears on the flag of Brazil, where it represents the state of Rio Grande do Sul.
- **The Triangle.** When Chinese astronomers adopted the European southern constellations, Atria became the third star of Sān Jiǎo Xíng, the Triangle.

An orange star marking the brightest corner of the Southern Triangle, not far from the Pointers, Alpha and Beta Centauri. Compare its warm orange with the whiter stars at the triangle’s other two corners.

## 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 21°N and never sets south of 21°S.

At its highest it stands below the horizon from 50°N, below the horizon from 35°N, 21° up from the equator, 56° up from 35°S.

## Facts

- Type: Star
- Constellation: Triangulum Australe
- Designations: Alpha Trianguli Australis, α TrA, HR 6217, HD 150798, HIP 82273
- Magnitude: 1.9
- Position: RA 16h 48.7m, Dec −69° 2′ (J2000)
- Spectral type: K2III_Ba1
- Colour: orange-red (B−V 1.45)
- Distance: 390 light-years
- Discovered: Naked-eye star of the far southern sky

Open AstroPilot to see when Atria (Alpha Trianguli Australis) is highest tonight from your location, how easy it is with your telescope or binoculars, and an eyepiece view. https://astropilot.space/object/atria