The Spring Triangle is an asterism that involves an imaginary triangle drawn upon the celestial sphere, with its defining vertices at Arcturus, Spica, and Regulus.
Key Facts & Summary
- The Spring Triangle asterism is visible in the southeastern sky of the northern hemisphere between March and May.
- Some sources include Denebola, the second-brightest star in Leo in this asterism. By Denebola’s inclusion, the asterism is more nearly equilateral.
- Denebola is only slightly fainter than Regulus.
- The stars that form the “true” Spring Triangle asterism, Arcturus, Spica, and Regulus also form another famous asterism, the Great Diamond, together with Cor Caroli.
- All of the stars in the Spring Triangle are the brightest stars in their respective constellations.
- Arcturus is the brightest star in Bootes, having an apparent magnitude of -0.05. This star is also the fourth brightest star in the night sky.
- Spica is the brightest star in Virgo, having an apparent magnitude of +0.97. Spica is also among the 20 brightest stars in the sky.
- Regulus is the brightest star in Leo, having an apparent magnitude of 1.40. It is the 21st brightest star in the night sky.
- Arcturus is the brightest star in the Spring Triangle asterism, and it is also the closest to us, at around 36.7 light-years away. It is also the brightest star in the Great Diamond asterism.
- Regulus is the faintest star in this asterism, and the second-closest to us, at a distance of 79.3 light-years away.
- Spica is the second-brightest star in the Spring Triangle, and the farthest away from us, at a distance of around 250 light-years.
- The Spring Triangle can be found by using the stars of one of the more famous asterisms, the Big Dipper. The line formed by the three stars of the Big Dippers’s handle leads to Arcturus, and then to Spica.
- Regulus can be found along a line extended from Megrez to Phecda, the two inner stars of the Dipper’s bowl.
The Spring Triangle asterism is a prominent asterism that can be seen in the southeastern sky of the northern hemisphere, during March and May. This asterism covers a portion of the Bootes, Virgo, and Leo constellations.
The Spring Triangle is one of several easily recognizable northern asterisms, such as the Summer Triangle, Cassopeia’s W, they Keystone in Hercules, the Water Jar in Aquarius, the Northern Cross in Cygnus, and the Circlet of Pisces in Pisces.
The Stars of the Spring Triangle
The stars of the Spring Triangle are among the most famous in the sky, being among the top brightest stars. Sometimes, one can use the Big Dipper asterism to find these stars.
Arcturus, designated as Alpha Bootis, is the brightest star in the constellation of Bootes, and the brightest star in the Spring Triangle and the Great Diamond asterism, having an apparent magnitude of -0.05.
Arcturus marks the western vertex of the asterism, and it is the closest star to us from this asterism, at only 36.7 light-years away. Arcturus is a red giant star, older than our Sun, being around 7.1 billion years old.
Arcturus has around 108% of our Sun’s mass, 2,540% of its radius, and it is 170 times brighter than our Sun. Though it is several times bigger than our Sun, it is much cooler, having temperatures of around 4,286 K.
The line formed by the three stars of the Big Dippers’s handle leads to Arcturus, and then to Spica. Regulus can be found along a line extended from Megrez to Phecda, the two inner stars of the Dipper’s bowl.
Spica, designated as Alpha Virginis, is the brightest star in the constellation of Virgo, and the second-brightest star of the Spring Triangle, and the Great Diamond asterism, having an apparent magnitude of +0.97.
Spica marks the southern vertex of the asterism, and it is the farthest star from the Spring Triangle, is situated at around 250 light-years away from us.
Spica is the 15th brightest star in the night sky, and it is a spectroscopic binary star, and a rotating ellipsoidal variable star – the two stars are so close that they are egg-shaped rather than spherical.
The primary star is a blue giant and a variable star of the Beta Cephei type, having 1,143% of our Sun’s mass, 747% of its radius, and being 20,512 times brighter than our Sun.
Spica is also 4.3 times hotter than our Sun, having temperatures of around 25,300 K. This star is also spinning very fast, having a rotational velocity of 165.3 km / 102.7 mi per second.
The secondary star of the Spica system has around 721% of our Sun’s mass, 374% of its radius, and it is 2,254 times brighter than our Sun. It is also several times hotter than our Sun, having temperatures of around 20,900 K, and it also spins fastly, with a rotational velocity of 58.8 km / 36.5 mi per second. Spica is quite a young star, being only 12.5 million years old.
Regulus, designated as Alpha Leonis, is the brightest star in the constellation of Leo. Regulus is the 21st brightest star in the night sky, having an apparent magnitude of 1.40.
It is the faintest star in the Spring Triangle asterism, and the second-closest to us, at a distance of around 79.3 light-years. Regulus is a quadruple star system composed out of two stars organized into two pairs.
The primary pair, Regulus A, contains a blue-white main-sequence star, and a suspected white dwarf star. Regulus is a subgiant star, having 380% of our Sun’s mass, 309% of its radius, and it is 288 times brighter than the Sun. The temperatures on Regulus have been estimated around 12,460 K, around twice as hot as our Sun.
Regulus is a fast-spinning star, with a rotational velocity recorded at 318 km / 197.5 mi per second. Because of this, the star is highly oblate in shape. The star is at its 96.5% of its critical angular velocity break-up.
Another consequence is the so-called gravity darkening effect – the photosphere at the star’s poles is hotter, and five times brighter than its equatorial region. Regulus is emitting polarized light because of this.
The Spring Triangle asterism, with its stars, can be used as a tool in finding several different famous deep-sky objects, most of them being situated in the Virgo Cluster, a huge cluster of galaxies situated between the stars Denebola, and Vindemiatrix in Virgo.
Several notable galaxies lie in the region between Regulus and Denebola, such as the Leo Triplet galaxies ( Messier 65, 66, and NGC 3628, the M96 Group (consisting of the galaxies Messier 95, 96, and 105), and at least nine other members.
The Bootes Dwarf Galaxy, and the globular cluster Messier 53 can be found near Arcturus, in the direction of Regulus. The galaxies Messier 85 and Messier 100 are found a bit further along the same line. They are situated in the Coma Berenices constellation.
Did you know?
- The ancient Persians regarded Regulus as one of the four stars of their monarchy.
- Spica is among the nearest massive binary systems to the Sun. A temple to Hathor in Thebes was oriented with reference to Spica when it was built in 3200 BC.
- Arcturus is known as the Guardian of the Bear. In Inuit astronomy, it is called the Old Man.