Triangulum Australe and Circinus
The Constellations of the Southern Triangle and the Drawing Compass
Aug 7, 2009
Triangulum Australe, the Southern Triangle, and Circinus, the Drawing Compass, are two constellations that border each other near the south celestial pole. The constellations are both south circumpolar, which means that for residents in the Southern Hemisphere the constellations never set and are always visible above the horizon. Triangulum Australe is the older of the two constellations, created in the 16th century. Circinus, being smaller and with fewer bright stars, is a new creation. Circinus was created in the 18th century. Circinus is a drawing compass and also shares the Southern Hemisphere with another compass, Pyxis the mariner's compass, although they are not close together in the sky.
How to Find Triangulum Australe and Circinus
Circinus is named for an old-fashioned drawing compass but in reality the constellation does not look like much because it only has one star above magnitude 4. It is relatively easy to find, though, because it is situated close to Alpha Centauri. Alpha Centauri, at magnitude -0.27, lies nearly on the border with Circinus. On the opposite side of Circinus from Centaurus is Triangulum Australe. Triangulum Australe does resemble a triangle, with its brightest corner star farthest from Alpha Centauri.
Stars in the Southern Triangle and Drawing Compass
Circinus's brightest star, Alpha Circini, is magnitude 3.18 and lies 53 light-years away. Seven and a half degrees away is the second brightest star, Beta Circini, at magnitude 4.07 and a distance of 97 light-years.
Triangulum Australe's three brightest stars are the three that mark each corner of the triangle. The brightest is Alpha Trianguli Australis, also known as Atria. Atria is magnitude 1.91 and lies 415 light-years away. The last two triangle stars are nearly the same magnitude. Beta Trianguli Australis lies between Atria and Beta Circini. Beta Trianguli Australis is magnitude 2.83 at a distance of 40 light-years. The last star in the triangle is Gamma Trianguli Australis at magnitude 2.86 and a distance of 183 light-years.
Star Clusters in the Constellations
On the northern borders of both constellations an open cluster awaits. The Southern Triangle's cluster is the brighter of the two. NGC 6025 is magnitude 5.09. The cluster lies about 2,000 light-years away and is a fair sight through binoculars.
Circinus's best open cluster is NGC 5823. It is magnitude 7.9 About three and a half degrees away is another cluster for telescope observers, NGC 5715, at magnitude 10.
Both Triangulum Australe and Circinus lie along the Milky Way, which makes them rich hunting grounds for simply scanning with a telescope and seeing what pops up.
 |
 |
