Beta Canis Majoris
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Beta Canis Majoris (β Canis Majoris, abbreviated Beta CMa, β CMa), also named Mirzam Template:IPAc-en,<ref name="IAU-CSN"/> is a star in the southern constellation of Canis Major, the "Great Dog", located at a distance of about 500 light-years (150 parsecs) from the Sun.<ref name=aaa474_2_653/> In the modern constellation it lies at the position of the dog's front leg.
NomenclatureEdit
Beta Canis Majoris is the star's Bayer designation. The traditional names Mirzam, Al-Murzim or Murzim,<ref name=allen1899/> derive from the Arabic (مرزم) for 'The Herald', and probably refer to its position, heralding (i.e., rising before) Sirius in the night sky. In 2016, the International Astronomical Union organized a Working Group on Star Names (WGSN)<ref name="WGSN"/> to catalog and standardize proper names for stars. The WGSN's first bulletin of July 2016<ref name="WGSN1"/> included a table of the first two batches of names approved by the WGSN; which included Mirzam for this star.
In Chinese, {{#invoke:Lang|lang}} ({{#invoke:Lang|lang}}), meaning 'Market for Soldiers', refers to an asterism consisting of β Canis Majoris, Nu3 Canis Majoris, 15 Canis Majoris, Pi Canis Majoris, Omicron1 Canis Majoris and Xi1 Canis Majoris.<ref name=zh/> Consequently, β Canis Majoris itself is known as {{#invoke:Lang|lang}} ({{#invoke:Lang|lang}}, Template:Langx).<ref name=lcsd/> From this Chinese name arose the name Kuen She.<ref name=allen1899/>
The Dunhuang Star Chart noted β Canis Majoris as Yeji "Pheasant Cock", though was located about 10 degrees too far north of its correct position.<ref name=ChineseSky/>
Beta Canis Majoris was called Oupo by the people of the Tuamotus.Template:Sfn
PropertiesEdit
Frequency (day−1) |
Amplitude (km s−1) |
---|---|
3.9793 | 2.7 |
3.9995 | 2.6 |
4.1832 | 0.7 |
Mirzam is a Beta Cephei variable that varies in apparent magnitude between +1.97 and +2.01 over a six-hour period, a change in brightness that is too small to be discerned with the naked eye. It exhibits this variation in luminosity because of periodic pulsations in its outer envelope, which follow a complex pattern with three different cycles; all about six hours in length. The two dominant pulsation frequencies have a combined beat period of roughly 50 days. The strongest pulsation mode is a radial first overtone, while the second is non-radial.<ref name=aaa459_2_589/>
This star has a mass of about 12–13 times the mass of the Sun with 7.4 or 8.2 times the Sun's radius.<ref name=fossati/> The effective temperature of the star's outer envelope is about 24,700 K,<ref name=schultz2019/> which is much higher than the Sun's at 5,778 K. The energy emitted at the high temperature of the former is what gives this star a blue-white hue characteristic of a B-type star.<ref name=csiro/> The estimated age of Mirzam is Template:Nowrap,<ref name=fossati/> which is long enough for a star of this mass to have evolved into a giant star. The stellar classification of B1 II-III<ref name=apj573_1_359/> indicates that the spectrum matches a star part way between a giant star and a bright giant. This star has a rotation period of 13.6 days and is inclined 57.6 ° as seen from Earth.<ref name=fossati/>
Beta Canis Majoris is located near the far end of the Local Bubble,<ref name=Welsh/> a cavity in the local interstellar medium through which the Sun is traveling. It is located within the Mirzam Tunnel, a region of less dense concentration between the stars and HII regions surrounding the Ori OB1 and Vel OB2 associations. Beta Canis Majoris was the brightest star in the night sky around four million years ago, peaking with an apparent magnitude of -3.65, or more than seven times as bright as Sirius today.<ref name=tomkin1998>Template:Cite journal – based on computations from HIPPARCOS data. (The calculations exclude stars whose distance or proper motion is uncertain.)</ref>
In cultureEdit
Mirzam appears on the flag of Brazil, symbolising the state of Amapá.<ref name=flag/>
Murzim (AK-95) was a United States Navy Crater class cargo ship named after one of the star's alternative traditional names.