Star Constellation Facts: Corona Borealis

Corona Borealis
Image Credit: Duncan Morgan

Corona Borealis (“the northern crown”) is a small but recognizable horseshoe shaped constellation that is found in a relatively empty part of northern sky. It is said to represent the crown of Ariadne, a princess and daughter of King Minos of Crete, who was given the gift by Dionysus, who after marrying her merrily tossed the crown into the celestial heavens where its jewels transformed into the stars of this beautiful constellation. Corona Borealis’s brightest member, Alphecca, is a white star situated 75 light years from Earth that shines with a visual magnitude of +2.23.


Corona Borealis is the 73rd largest constellation, taking up an area of 179 square degrees of the northern celestial hemisphere. It can be seen by observers located between +90° and -50° of latitude, although best viewed from April to June. The constellation’s bordering Corona Borealis includes Hercules to its east, Boötes to its north and west, and Serpens Caput to its south.

Ursa Major Family

Corona Borealis is a member of the Ursa Major family of constellations, together with Coma Berenices, Boötes, Camelopardalis, Canes Venatici, Draco, Leo Minor, Lynx, Ursa Major and Ursa Minor.


Corona Borealis is associated with the crown of Ariadne, which was created by Hephaestus and worn by the Cretan Princess on her wedding day to Dionysus. According to Greek myth, Ariadne helped the hero Theseus to slay her half-brother the Minotaur, and navigate his way out of the labyrinth in return for his promising to marry her. Once the mission was completed, Theseus abandoned Ariadne on the island of Naxos before traveling onto his native Athens, but after the god Dionysus came upon her he fell instantly in love. Once they got married, the crown she wore during the wedding ceremony was tossed into the sky where its jewels became the stars of the constellation Corona Borealis.

Principal Stars

There are 7 stars that make up the constellation’s horse-shoe shape, the brightness of which is Alpha Coronae Borealis, with the remaining six all being 4th-magnitude stars, namely Theta, Beta, Gamma, Delta, Epsilon and Iota Coronae Borealis.

Corona Borealis Stars– Alphecca (Alpha Coronae Borealis), the constellation’s brightest star, is a binary star found 75 light years from our solar system of magnitude 2.23. Its main component is a white main sequence star (A0V) with around 3 times the Sun’s size and 2.6 times its mass, while its companion is a yellow star (G5) that has around 90% the Sun’s size and mass, and 30 times its luminosity. The binary system has a separation of around 0.20 AU and an orbital period of 17.36 days. Alphecca means “the bright one of the broken ring” in Arabic, while the star’s other name, Gemma, means “jewel” in Latin.

– Nusakan (Beta Coronae Borealis), the second brightest star in Corona Borealis, is a binary system situated 114 light years away from Earth. Being a variable star, it has a visual magnitude that ranges from 3.65 to 3.72 over an 18.487 day period. The system’s primary component is a blue dwarf (A5V) with 2.63 times the Sun’s size, 2.09 its mass, and 25.3 times its luminosity; while its companion is a blue-white dwarf (F2V) which is 1.56 times bigger than the Sun, with 1.4 times its mass, and 5 times its brightness. The system has an estimated age of around 530 million years.

– Gamma Coronae Borealis, the constellation’s third brightest star, is a binary system found 170 light years distant of magnitude 3.84. Its main component is a blue dwarf (B9V) with 1.9 times the Sun’s size, 2.6 times its mass, and 48 times its luminosity, while its fainter companion is another blue dwarf (A3V) that is 1.3 times bigger than the Sun, with 1.85 times its mass, and 9 times its brightness. The pair are separated by 32.7 AU, and have an orbital period of 92.94 years.

Other stars of interest in Corona Borealis includes two notable variable stars, with the red giant T Coronae Borealis (Blaze Star) exhibiting a visual magnitude that can vary from as low as 2.0 during outbursts to as high as 10.8; and R Coronae Borealis (Fade-Out Star), a yellow supergiant whose luminosity can range from 5.71 to 14.8. Corona Borealis also contains the pulsating white dwarf TY Coronae Borealis; the yellow dwarf star Rho Coronae Borealis; the orange subgiant Kappa Coronae Borealis; as well as several binary stars, including Eta Coronae Borealis, Sigma Coronae Borealis and U Coronae Borealis.

Notable Deep-Sky Objects

Corona Borealis Galaxy Cluster
Corona Borealis Galaxy Cluster

There are no Messier objects in Corona Borealis, but it does contain a number of deep-sky objects, the most noticeable of which is the Corona Borealis Galaxy Cluster (Abell 2065), a supercluster of around 400 galaxies spread over a region of space 330 million light-years wide, and 130 million light years deep. It is from 1 to 1.5 billion light years away, and can be found in the southwest corner of Corona Borealis with a visual magnitude of 16.5.

Other objects of interest in the constellation includes several galaxies, such as the spiral galaxy NGC 6085; and the elliptical galaxy NGC 6086; as well as a number of galaxy clusters, including the vast 6 million light-year wide galaxy cluster of Abell 2142; and the 3.9 billion light-year distant galaxy cluster RX J1532.9+3021, whose center contains an elliptical galaxy with one of the most massive supermassive black holes ever discovered.

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