Tucana

Tucana (The Toucan) is a constellation in the southern sky, named after the toucan, a South American bird. It is one of twelve constellations conceived in the late sixteenth century by Petrus Plancius from the observations of Pieter Dirkszoon Keyser and Frederick de Houtman. Tucana first appeared on a 35-centimetre-diameter (14 in) celestial globe published in 1598 in Amsterdam by Plancius and Jodocus Hondius and was depicted in Johann Bayer's star atlas Uranometria of 1603. French explorer and astronomer Nicolas Louis de Lacaille gave its stars Bayer designations in 1756. The constellations Tucana, Grus, Phoenix and Pavo are collectively known as the "Southern Birds".

Tucana is not a prominent constellation as all of its stars are third magnitude or fainter; the brightest is Alpha Tucanae with an apparent visual magnitude of 2.87. Beta Tucanae is a star system with six member stars, while Kappa is a quadruple system. The constellation contains 47 Tucanae, one of the brightest globular clusters in the sky, and most of the Small Magellanic Cloud.

Tucana is one of the twelve constellations established by the astronomer Petrus Plancius from the observations of the southern sky by the Dutch explorers Pieter Dirkszoon Keyser and Frederick de Houtman, who had sailed on the first Dutch trading expedition, known as the Eerste Schipvaart, to the East Indies. It first appeared on a 35-centimetre-diameter (14 in) celestial globe published in 1598 in Amsterdam by Plancius with Jodocus Hondius. The first depiction of this constellation in a celestial atlas was in the German cartographer Johann Bayer's Uranometria of 1603. Both Plancius and Bayer depict it as a toucan. De Houtman included it in his southern star catalogue the same year under the Dutch name Den Indiaenschen Exster, op Indies Lang ghenaemt "the Indian magpie, named Lang in the Indies", by this meaning a particular bird with a long beak—a hornbill, a bird native to the East Indies. A 1603 celestial globe by Willem Blaeu depicts it with a casque. It was interpreted on Chinese charts as Niǎohuì "bird's beak", and in England as "Brasilian Pye", while Johannes Kepler and Giovanni Battista Riccioli termed it Anser Americanus "American Goose", and Caesius as Pica Indica. Tucana and the nearby constellations Phoenix, Grus and Pavo are collectively called the "Southern Birds".

Irregular in shape, Tucana is bordered by Hydrus to the east, Grus and Phoenix to the north, Indus to the west and Octans to the south. Covering 295 square degrees, it ranks 48th of the 88 constellations in size. The recommended three-letter abbreviation for the constellation, as adopted by the International Astronomical Union in 1922, is "Tuc". The official constellation boundaries, as set by Belgian astronomer Eugène Delporte in 1930, are defined by a polygon of 10 segments. In the equatorial coordinate system, the right ascension coordinates of these borders lie between 22^h 08.45^m and 01^h 24.82^m , while the declination coordinates are between −56.31° and −75.35°. As one of the deep southern constellations, it remains below the horizon at latitudes north of the 30th parallel in the Northern Hemisphere, and is circumpolar at latitudes south of the 50th parallel in the Southern Hemisphere.

Although he depicted Tucana on his chart, Bayer did not assign its stars Bayer designations. French explorer and astronomer Nicolas Louis de Lacaille labelled them Alpha to Rho in 1756, but omitted Omicron and Xi, and labelled a pair of stars close together Lambda Tucanae, and a group of three stars Beta Tucanae. In 1879, American astronomer Benjamin Gould designated a star Xi Tucanae—this had not been given a designation by Lacaille who had recognized it as nebulous, and it is now known as the globular cluster 47 Tucanae. Mu Tucanae was dropped by Francis Baily, who felt the star was too faint to warrant a designation, and Kappa's two components came to be known as Kappa¹ and Kappa².

The layout of the brighter stars of Tucana has been likened to a kite. Within the constellation's boundaries are around 80 stars brighter than an apparent magnitude of 7. At an apparent magnitude of 2.86, Alpha Tucanae is the brightest star in the constellation and marks the toucan's head. It is an orange subgiant of spectral type K3III around 199 light-years distant from the Solar System. A cool star with a surface temperature of 4300 K, it is 424 times as luminous as the Sun and 37 times its diameter. It is 2.5 to 3 times as massive. Alpha Tucanae is a spectroscopic binary, which means that the two stars have not been individually resolved using a telescope, but the presence of the companion has been inferred from measuring changes in the spectrum of the primary. The orbital period of the binary system is 4197.7 days (11.5 years). Nothing is known about the companion. Two degrees southeast of Alpha is the red-hued Nu Tucanae, of spectral type M4III and lying around 290 light-years distant. It is classified as a semiregular variable star and its brightness varies from magnitude +4.75 to +4.93. Described by Richard Hinckley Allen as bluish, Gamma Tucanae is a yellow-white sequence star of spectral type F4V and an apparent magnitude of 4.00 located around 75 light-years from Earth. It also marks the toucan's beak.

Beta, Delta and Kappa are multiple star systems containing six, two and four stars respectively. Located near the tail of the toucan, Beta Tucanae's two brightest components, Beta¹ and Beta² are separated by an angle of 27 arcseconds and have apparent magnitudes of 4.4 and 4.5 respectively. They can be separated in small telescopes. A third star, Beta³ Tucanae, is separated by 10 arcminutes from the two, and able to be seen as a separate star with the unaided eye. Each star is itself a binary star, making six in total. Lying in the southwestern corner of the constellation around 251 light-years away from Earth, Delta Tucanae consists of a blue-white primary contrasting with a yellowish companion. Delta Tucanae A is a main sequence star of spectral type B9.5V and an apparent magnitude of 4.49. The companion has an apparent magnitude of 9.3. The Kappa Tucanae system shines with a combined apparent magnitude of 4.25, and is located around 68 light-years from the Solar System. The brighter component is a yellowish star, known as Kappa Tucanae A with an apparent magnitude of 5.33 and spectral type F6V, while the fainter lies 5 arcseconds to the northwest. Known as Kappa Tucanae B, it has an apparent magnitude of 7.58 and spectral type K1V. Five arcminutes to the northwest is a fainter star of apparent magnitude 7.24—actually a pair of orange main sequence stars of spectral types K2V and K3V, which can be seen individually as stars one arcsecond apart with a telescope such as a Dobsonian with high power.

Lambda Tucanae is an optical double—that is, the name is given to two stars (Lambda¹ and Lambda²) which appear close together from the Earth, but are in fact far apart in space. Lambda¹ is itself a binary star, with two components—a yellow-white star of spectral type F7IV-V and an apparent magnitude of 6.22, and a yellow main sequence star of spectral type G1V and an apparent magnitude of 7.28. The system is 186 light-years distant. Lambda² is an orange subgiant of spectral type K2III that is expanding and cooling and has left the main sequence. Of apparent magnitude 5.46, it is approximately 220 light-years distant from Earth.