Beta Carinae is the second-brightest star in the southern constellation of Carina. It has the official name Miaplacidus; Beta Carinae is the star's Bayer designation, which is Latinised from β Carinae and abbreviated Beta Car or β Car. With apparent magnitude of 1.69, it is one of the brightest stars in the night sky. It is the brightest star in the southern asterism known as the Diamond Cross, marking the southwestern end of the asterism. It lies near the planetary nebula IC 2448. Parallax measurements place it at a distance of from the Sun.
Nomenclature β Carinae (Latinised to Beta Carinae) is the star's Bayer designation. It was also designated as the alpha (α) star of Edmond Halley's now-obsolete constellation Robur Carolinum.
The star's historical name Miaplacidus made its debut on star maps in 1856 when the star atlas Geography of the Heavens, composed by , was published. The meaning and linguistic origin of the name is uncertain; placidus is from Latin for 'placid', while William Higgins, a 19th-century scholar on star names, surmised that the first part of the name is from Arabic miyāh for 'waters'. The IAU Working Group on Star Names first bulletin of July 2016 included a table of the first two batches of names approved by the WGSN; which included Miaplacidus for this star.
In Chinese, (), meaning Southern Boat, refers to an asterism consisting of β Carinae, V337 Carinae, PP Carinae, θ Carinae and ω Carinae. 中國星座神話, written by 陳久金. Published by 台灣書房出版有限公司, 2005, . Consequently, β Carinae itself is known as (, ). 香港太空館 - 研究資源 - 亮星中英對照表 , Hong Kong Space Museum. Accessed on line November 23, 2010.
Physical properties The stellar classification of A1 III mean that Miaplacidus is an evolved giant star that has exhausted the hydrogen at its core and has expanded. It has an estimated age of 260 million years. This star does not show an excess emission of infrared radiation that might otherwise suggest the presence of a debris disk. It has about 3.8 times the Sun's mass and has expanded to almost six times the radius of the Sun. Presently it is radiating 223 times as much luminosity as the Sun from its outer envelope at an effective temperature of . Despite its enlarged girth, this star still shows a rapid rotation rate, with a projected rotational velocity of .
References Note: see VizieR catalogue I/311.