Key Facts & Summary
- The Great Diamond is formed out of four prominent stars – Cor Caroli designated as Alpha Canum Venaticorum, located in Canes Venatici, Denebola / Beta Leonis, located in Leo, Spica / Alpha Virginis, located in Virgo, and Arcturus / Alpha Bootis, the brightest star in the constellation of Bootes.
- The Great Diamond asterism is larger than the more famous Big Dipper asterism.
- The three southernmost stars in the Great Diamond are often regarded as being their own asterism, the Spring Triangle.
- Arcturus, Spica, and Denebola form the Spring Triangle asterism even though Regulus, the brightest star in Leo, is usually taken as the third vertex of the asterism.
- Within the Great Diamond, many of the stars belong to the Corona Berenices constellation. Many nearby galaxies, including galaxies in the Virgo Cluster, are within this asterism, and some of these galaxies can be easily observed with an amateur telescope.
- The Great Diamond is seen in the northern hemisphere in the evening during the months of spring.
- The Great Diamond asterism is called the Great Diamond of Virgo since Spica, Virgo’s brightest star, forms the base of the diamond-shaped pattern.
- The brightest star in the Great Diamond asterism is Arcturus, which has an apparent magnitude of -0.05. It is the fourth brightest star in the night sky.
- The second brightest star in the Great Diamond is Spica, which usually has an apparent magnitude of 0.95. Spica is the 15th brightest star in the night sky.
- Denebola marks the eastern vertex of the Great Diamond, and it has an apparent magnitude of 2.1.
- Cor Caroli marks the northern vertex of the Great Diamond, and it has an apparent magnitude of 2.81.
The Great Diamond asterism contains the brightest stars of Bootes, Virgo, and Canes Venatici constellations, and the second brightest star of the Leo constellation, Denebola.
This asterism has a diamond-shaped pattern, and though it contains portions of the Bootes, Virgo, Canes Venatici, and Leo constellations, the asterism also almost completely encloses the constellation Coma Berenices.
Thus, the region of the sky framed by the Great Diamond asterism contains several interesting deep-sky objects and even Messier objects. The asterism can be used as a reference point to find them.
The Stars of the Great Diamond
The best time to view the Great Diamond asterism is during the evenings in the months of spring, in the northern celestial hemisphere. The stars forming the Great Diamond are among the brightest stars in the night sky.
Arcturus, designated as Alpha Bootis, is the brightest star in the constellation of Bootes, and the brightest star in the Great Diamond asterism, having an apparent magnitude of -0.05.
Arcturus marks the western vertex of the asterism, and it is the second-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.
Spica, designated as Alpha Virginis, is the brightest star in the constellation of Virgo, and the second-brightest star of 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 Great Diamond, 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.
Denebola, also designated as Beta Leonis, is the second-brightest star in the constellation of Leo, and the third brightest in the Great Diamond asterism.
Denebola is an A-type main-sequence star, located at around 35.9 light-years away from us. This makes Denebola the closest star to us from the Great Diamond asterism.
Denebola has an apparent magnitude of 2.113, and it is 15 times brighter than our Sun. It has around 178% of our Sun’s mass, 172% of its radius, and it is hotter than our Sun, having temperatures of around 8,500 K.
This star is also spinning fast, having a rotational velocity of around 128 km / 79.5 mi per second. It is also a young star, being between 100 to 380 million years old. Denebola marks the eastern vertex of the Great Diamond asterism.
Cor Caroli, designated as Alpha Canum Venaticorum, is the brightest star in the constellation of Canes Venatici, and the faintest star of the Great Diamond asterism.
Cor Caroli is actually a binary star system, with a combined apparent magnitude of 2.81. This star system is situated at around 120 light-years from us, being the second-farthest star in the Great Diamond.
Cor Caroli marks the northern vertex of the Great Diamond asterism. The primary star, designated as Alpha Canum Venaticorum A2, is a chemically peculiar star that has a magnetic field which is 5,000 times stronger than that of Earth’s.
Alpha Canum Venaticorum A2 is also classified as an Ap/Bp star – its atmosphere showing abundances of certain elements, such as silicon, mercury, and europium.
The secondary star, designated as Alpha Canum Venaticorum A1, is an F-type main-sequence star that is fainter than the primary star, having an apparent magnitude of 5.60.
Alpha Canum Venaticorum A1 has around 147% of our Sun’s mass, 150% of its radius, and it is hotter than our Sun, having temperatures of around 7,080 K.
Alpha Canum Venaticorum A2 is even more impressive, having 297%% of our Sun’s mass, 249% of its radius, and having temperatures of around 11,600 K.
The Great Diamond asterism, or its stars, can be used as a guide in finding many interesting deep-sky objects in the constellations of Bootes, Canes Venatici, Virgo, Leo, and Coma Berenices.
Arcturus, for example, lies in the same region of the sky as the Bootes Dwarf Galaxy, in the direction of Spica. The globular cluster Messier 3, located in Canes Venatici, is located roughly halfway from Cor Caroli to Arcturus.
The globular cluster Messier 53 is 15 degrees west of Arcturus, in Coma Berenices. The Whale Galaxy and the Hockey Stick Galaxies in Canes Venatici can be seen just under Cor Caroli, in the direction of Denebola.
The Black Eye Galaxy / Messier 64, lies 19 degrees west and a little north of Arcturus, not far from Messier 53. It can be viewed even through 4-inch telescopes. The Needle Galaxy is in the upper corner of the Great Diamond, in Coma Berenices.
All of the stars in the Great Diamond asterism can be used to find several other deep-sky objects, especially Cor Caroli.
Did you know?
- Cor Caroli can be used to find many famous deep-sky objects that lie even outside of the Great Diamond asterism.
- Spica is on the flag of the Brazilian state of Para, and it also represents this star on the official flag of Brazil.
- In astrology, Denebola was believed to portend misfortune and disgrace.
- In the Middle Ages, Arcturus was considered a Behenian Fixed Star, and it was used in magic rituals.