Triangulum Australe
What is Triangulum Australe?
Constellations· Southern winter · a crisp triangle southeast of Alpha Centauri. The southern triangle. It covers slightly less sky than the northern Triangulum, but its stars are far brighter, making it one of the easiest southern constellations to recognise.
📍 Visible from where you are right now — computed in your browser
Stars of the figure
| Star | Magnitude |
|---|---|
| Atria | 1.9 |
The 1 brightest of the 3 stars used in the figure (3 lines). Lower magnitude means brighter.
Constellation basics
| Season | Jun–Jul evenings; never visible from London or New York |
|---|---|
| Brightest star | Atria, mag 1.9 |
| How to find | a short hop southeast of Alpha Centauri and Hadar |
| Area rank | 83rd of 88 |
Figures are representative approximations. Source: compiled from NASA and IAU public data.
The southern triangle on Brazil's flag
Triangulum Australe also appears on a national flag. The blue disc in the middle of Brazil's flag is scattered with stars. They copy the sky over Rio de Janeiro on 15 November 1889, the day Brazil became a republic. Along with the Southern Cross, the three stars of Triangulum Australe are in that disc.
Each star on the flag stands for one of Brazil's states. In Triangulum Australe, Atria represents Rio Grande do Sul, Beta represents Santa Catarina and Gamma represents Paraná. The first flag had 21 stars, and as new states were added the number grew to today's 27.
At the northern edge of the constellation lies the open cluster NGC 6025. Lacaille found it in the early 1750s while observing from the Cape of Good Hope. About 30 stars are loosely gathered some 2,500 light-years away. It shows well in binoculars, so southern observers often look for it first.
The constellation in depth
Triangulum Australe is one of twelve southern constellations that came from Dutch navigators' observations in the 1590s, and it appeared in Bayer's atlas of 1603. As its name says, it pairs with the northern Triangulum. It covers slightly less sky than its northern partner, but its three stars are much brighter, so it stands out far more.
Its brightest star, Atria, is an orange giant of magnitude 1.9. The name is a modern shortening of 'Alpha Trianguli Australis', made official by the International Astronomical Union in 2016. Many southern stars have no old Arabic names, so newly made names like this are sometimes used.
The three corner stars look alike in brightness, but their distances differ a great deal. Atria is about 400 light-years away, Gamma about 180 and Beta about 40. Atria looks brightest even though it is farthest because it really is thousands of times more luminous than the Sun. The neat triangle exists only as seen from Earth.
At declinations of −60° to −70° it cannot be seen from Europe or most of the United States. From the southern hemisphere it is visible nearly all year and best on June and July evenings: move your eyes a little south-east from bright Alpha Centauri and Hadar to find the crisp triangle. In the Sky view, set Sydney on a July evening to see it.
Frequently asked
- When can I see Triangulum Australe?
- Triangulum Australe is best seen in Jun–Jul evenings; never visible from London or New York.
- How do I find Triangulum Australe?
- To find Triangulum Australe, look for a short hop southeast of Alpha Centauri and Hadar.
- What is the brightest star in Triangulum Australe?
- The brightest star in Triangulum Australe is Atria, at magnitude 1.9.
Related
Figures are representative approximations. Simulated positions use J2000 mean elements.