Night Sky

The Spring Triangle

Tonight, a full moon and the Spring Triangle will cross the heavens together until almost dawn tomorrow. The Spring Triangle is an asterism made up of the bright stars Arcturus, Spica and Regulus at its corners. Arcturus is in Boötes the Herdsman, Spica is in Virgo the Maiden and Regulus is in Leo the Lion.

Arcturus, only 37 light-years away from us, is the closest giant star to Earth. In visible light, the star is 113 times brighter than our Sun and it contains about 1.5 times as much mass as our Sun. However, its reddish-orange color means the star is no longer fusing hydrogen in its core.

Spica, about 250 light-years away, has a visual luminosity about 2300 times the Sun's. In fact, Spica consists of two stars so close together they orbit each other every 4 days and they distort each other tidally, presenting different diameters as they orbit one another.

Regulus, roughly 77.5 light-years from Earth's Solar System is 140 times as bright as our Sun and its surface temperature is twice as hot, as well. Regulus is closest to the ecliptic (the Sun's annual path around the celestial sphere) of the 100 brightest stars and, in this position, the star is often occluded by the moon, and sometimes by Venus and Mercury.