Dorado is one of 12 southern constellations included by Petrus Plancius in his celestial globe of 1598 that were based upon the observations of Dutch explorers Pieter Dirkszoon Keyser and Frederick de Houtman. These new constellations were typically named after exotic animals, in this case a “dolphinfish”, and by 1603 their acceptance was assured after German astronomer Johann Bayer included them in his star atlas called Uranometria. The constellation of Dorado is faint, with its brightest star, alpha Doradus, a binary system consisting of two bluish stars situated 169 light-years distant with a combined visual magnitude of +3.27.
Dorado represents the tropical dwelling dolphinfish that Dutch navigators saw hunting flying fish during their voyages to the East Indies (Southeast Asia). Their observations led to the creation of two new constellations, Dorado (dolphinfish) and Volans (flying fish), which were subsequently placed in the night sky next to each other as if in pursuit. Also known as mahi-mahi, dolphinfish are ray-finned fish, and are not related to dolphins, which are mammals.
Dorado is the 72nd largest constellation in the night sky, and can be seen by observers located between +20° and -90° of latitude, although it is best seen from November to May. Dorado can be found just south west Canopus, a brilliant yellowish-white star that is the night sky’s second most luminous at visual magnitude 0.72. Although a small constellations, Dorado is quite long and so borders a number of other constellations including Caelum, Horologium, Hydrus, Reticulum, Mensa, Volans and Pictor.
Bayer Constellation Family
Dorado is a member of the Johann Bayer family of constellations, together with Hydrus, Volans, Apus, Pavo, Grus, Phoenix, Tucana, Indus, Chamaeleon and Musca.
– Alpha Doradus, the constellation’s brightest star, is a blue-white star around 169 light-years away whose magnitude varies between 3.26 and 3.30. It is actually a binary system comprised of a primary giant star and a subgiant star with an orbital period of around 12 years.
– Beta Doradus is a Cepheid variable whose brightness varies from 3.45 to 4.05 magnitudes over a 9.842 day period. It is the second brightest star in Dorado, and is located around 1,050 light-years away from Earth.
– Gamma Doradus, the third brightest star in Dorado, is a white dwarf around 66.2 light-years away with a visual magnitude of 4.25. It is the prototype of a type of star known as a Gamma Doradus variables, which are pulsating stars whose luminosity changes by less than a tenth of magnitude due to non-radial gravity wave oscillations.
Other stars of interest in Dorado include Delta Doradus, which is our moon’s south pole star; the red giant R Doradus, which is a Mira variable; the hypergiant S Doradus; and Zeta Doradus, a yellow-white dwarf star found 38 light years distant that shines with a visual magnitude of 4.68.
Notable Deep Sky Objects
There are no Messier objects in Dorado, but the constellation does contain the Large Magellanic Cloud, a satellite galaxy of our own Milky Way which has a number of notable deep sky objects.
– Large Magellanic Cloud (LMC) is an irregular galaxy that straddles both the constellations of Dorado and Mensa. At 157,000 light-years distant, it is our third closest galaxy, but is only around 1/100 as massive as the Milky Way. It is 14,000 light years across, has a visual magnitude of 0.9, and contains 60 globular star clusters, 700 open clusters and 400 planetary nebulae. The LMC looks irregular due to its tidal interactions with the Milky Way and another galaxy located in the Tucana constellation.
Despite the satellite galaxy being mentioned in the Middle Ages by Persian astronomer Al-Sufi in his “Book of Fixed Stars” (964 AD), it was eventually named after Portuguese explorer Ferdinand Magellan who observed it during his world circumnavigation of 1519–1522.
– Tarantula Nebula (NGC 2070) is located within the Large Magellanic Cloud, and was once thought to be a star until 1751, when it was confirmed as a nebula by the French astronomer Nicolas Louis de Lacaille. This nebula is around 160,000 light-years away, 500 light-years across, and has an apparent magnitude of 8, but an extremely bright absolute magnitude of -11.7. This nebula is also notable for being the largest region in the Local Group of galaxies, as well as its most active star-forming area.
– The Ghost Head Nebula (NGC 2080) is found southwards of the Tarantula Nebula, and is 50 light-years across and around 160,000 light-years away. It is in located in another star forming area of Dorado, and its name comes from its distinct white spots, known as the “eyes of the ghost.” The white spot to the west is called A1, with the hot, glowing bubble caused by a massive star at its core, while the eastern white spot, A2, contains a new cluster of young, massive stars.
Other deep-sky objects of interest in Dorado includes numerous globular clusters, such as NGC 2164, NGC 1755, NGC 1850, NGC 1854; as well as several open clusters, such as NGC 1820, NGC 1869, NGC 1901, and NGC 1910.