X Trianguli Australis

X Trianguli Australis is one of a relatively rare class of stars known as carbon stars, in whose atmospheres the element of carbon predominates, giving the star are unusually deep red colour. This a giant star with an estimated diameter some four hundred times that of the Sun, sufficient to engulf the entire inner Solar System if the star lay at its centre.

X Trianguli Australis is several hundred times more luminous than the Sun, but a distance of more than a thousand light years, it lies close to the limit of naked-eye visibility as seen from Earth. Its brightness is highly variable, and patterns of pulsation cause the star's luminosity to change gradually over time, so that its apparent brightness can rise or fall by up to a magnitude. There are two separate patterns of pulsation, each with a period of over a year, with one cycle taking 385 days, and the other 455 days to complete.