Delta Canis Majoris

Delta Canis Majoris (Latinised from δ Canis Majoris, abbreviated Delta CMa, δ CMa), officially named Wezen, is a star in the constellation of Canis Major. It is a yellow-white F-type supergiant with an apparent magnitude of +1.83. Since 1943, the spectrum of this star has served as one of the stable anchor points by which other stars are classified.

Observation
Delta Canis Majoris is the third-brightest star in the constellation after Sirius and ε Canis Majoris (Adhara), with an apparent magnitude of +1.83, and is white or yellow-white in colour. Lying about 10 degrees south southeast of Sirius, it only rises to about 11 degrees above the horizon at the latitude of the United Kingdom. The open cluster NGC 2354 is located only 1.3 degrees east of Delta Canis Majoris. As with the rest of Canis Major, Delta Canis Majoris is most visible in winter skies in the northern hemisphere, and summer skies in the southern. In Bayer's Uranometria, it is in the Great Dog's hind quarter.

History and naming
δ Canis Majoris (Latinised to Delta Canis Majoris) is the star's Bayer designation.

The traditional name, Wezen (alternatively Wesen, or Wezea), is derived from the medieval Arabic وزن al-wazn, which means 'weight' in modern Arabic. The name was for one of a pair of stars, the other being Hadar, which has now come to refer to Beta Centauri. It is unclear whether the pair of stars was originally Alpha and Beta Centauri or Alpha and Beta Columbae. In any case, the name was somehow applied to both Delta Canis Majoris and Beta Columbae. Richard Hinckley Allen muses that the name alludes to the difficulty the star has rising above the horizon in the northern hemisphere. Astronomer Jim Kaler has noted the aptness of the traditional name given the star's massive nature.

In 2016, the International Astronomical Union organized a Working Group on Star Names (WGSN) to catalog and standardize proper names for stars. The WGSN's first bulletin of July 2016 included a table of the first two batches of names approved by the WGSN; which included Wezen for this star.

In Chinese, 弧矢 (Hú Shǐ), meaning Bow and Arrow, refers to an asterism consisting of δ Canis Majoris, ε Canis Majoris, η Canis Majoris, κ Canis Majoris, ο Puppis, π Puppis, χ Puppis, c Puppis and k Puppis. Consequently, δ Canis Majoris itself is known as 弧矢一 (Hú Shǐ yī, the First Star of Bow and Arrow.)

In the catalogue of stars in the Calendarium of Al Achsasi Al Mouakket, this star was designated Thalath al Adzari (تالت ألعذاري - taalit al-aðārii), which was translated into Latin as Tertia Virginum, meaning the third virgin. This star, along with ε Canis Majoris (Adhara), η Canis Majoris (Aludra) and ο2 Canis Majoris (Thanih al Adzari), were Al ʽAdhārā (ألعذاري), the Virgins.

Physical properties
Delta Canis Majoris is a supergiant of class F8. Its surface temperature is around 5,818 K, and it is 14 times more massive than the Sun. Its absolute magnitude is −5.97, and it lies around 1,600 light-years away. It is rotating at a speed of around 28 km/s, and hence may take a year to rotate fully. Only around 10 million years old, Delta Canis Majoris has stopped fusing hydrogen in its core. Its outer envelope is beginning to expand and cool, and in the next 100,000 years it will become a red supergiant as its core fuses heavier and heavier elements. Once it has an iron core, it will collapse and explode as a supernova.

The angular diameter of Wezen has been measured using interferometry, giving a limb-darkened diameter of $13.4$. J Davis et al. (2007) used this angular diameter and calculated a physical radius of $3.633 milliarcseconds$ using a parallax of $215 solar radius$ measured by the Hipparcos specrcaft, which implies a distance of $1.82 milliarcseconds$. Since then, the 2007 Hipparcos reduction refined the parallax to $1,800 light-years$, corresponding a distance of about $2.03 mas$ (493 parsecs). This distance gives a smaller radius of using the angular diameter. A 2010 study gives a luminosity and temperature implying a radius of, while a 2017 study published a radius of.

If Delta Canis Majoris were as close to Earth as Sirius is, it would be as bright as a half-full moon.

Modern legacy
Delta Canis Majoris appears on the flag of Brazil, symbolising the state of Roraima.