<templatestyles src="Template:Sky/styles.css" />Coordinates: Sky map 11h 01m 50.5s, +56° 22′ 57″

Merak (star)

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Template:Short description

Merak
Template:Location mark
Location of Merak (circled)
Observation data
Epoch J2000.0      Equinox J2000.0
Constellation Ursa Major
Right ascension Template:RA[1]
Declination Template:DEC[1]
Apparent magnitude (V) +2.37[2]
Characteristics
Evolutionary stage Main sequence[3]
Spectral type A1IVps[4]
U−B Template:Engvar +0.00[2]
B−V Template:Engvar -0.02[2]
Variable type Suspected
Astrometry
Radial velocity (Rv)-12.0[5] km/s
Proper motion (μ) RA: +81.43[1] mas/yr
Dec.: +33.49[1] mas/yr
Parallax (π)40.90±0.16 mas[1]
DistanceTemplate:Rnd ± Template:Rnd ly
(Template:Rnd ± Template:Rnd pc)
Absolute magnitude (MV)+0.61[6]
Details[7]
MassScript error: No such module "val". Template:Solar mass
RadiusScript error: No such module "val". Template:Solar radius
Luminosity63.5 Template:Solar luminosity
Surface gravity (log g)Script error: No such module "val". cgs
TemperatureScript error: No such module "val". K
Rotational velocity (v sin i)Script error: No such module "val". km/s
AgeScript error: No such module "val". Myr
Metallicity [Fe/H]{{{metal_fe2}}} dex
Other designations
Merak, Mirak,[8] β Ursae Majoris, β UMa, Beta UMa, 48 Ursae Majoris, BD+57°1302, FK5 416, GC 15145, HD 95418, HIP 53910, HR 4295, PPM 32912, SAO 27876[9]
Database references
SIMBADdata

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File:Sun to Arcturus comparison.jpg
Size comparison between the Sun, Beta Ursae Majoris, Pollux, and Arcturus.

Merak Script error: No such module "IPAc-en"., also called Beta Ursae Majoris (β Ursae Majoris, abbreviated Beta UMa, β UMa),[10][11] is a star in the northern constellation of Ursa Major.

The apparent visual magnitude of this star is +2.37,[2] which means it is readily visible to the naked eye. It is more familiar to Northern Hemisphere observers as one of the "pointer stars" in the Big Dipper, or the Plough (UK), which is a prominent asterism of seven stars that forms part of the larger constellation. Extending an imaginary straight line from this star through the nearby Alpha Ursae Majoris (Dubhe) extends to Polaris, the north star.

Spectral classification

In 1943, β Ursae Majoris was listed as a spectral standard for the class of A1 V.[12] When improved instruments made it possible to identify subgiant luminosity classes for early A-class stars, β Ursae Majoris was assigned that class A0 IV.[13] This was later revised to A1 IV.[4] It is considered to be a mild Am star, a type of chemically peculiar star with unusually strong lines of certain metallic elements.[14]

Properties

Based upon parallax measurements, β Ursae Majoris is located at a distance of Script error: No such module "convert". from the Sun. Although the spectrum has a luminosity class of a subgiant,[4] stellar evolution models indicate that it is still on the main sequence, having gone through three-quarters of its main sequence lifetime.[3] The effective temperature of the outer envelope is about 9,225 K,[15] giving it a white-hued glow that is typical for A-type stars.[16] It is larger than the Sun, with about 2.7 times the mass and 2.84 times the solar radius. If they were viewed from the same distance, Beta Ursae Majoris would appear much brighter than the Sun, as it is radiating 68 times the Sun's luminosity.[15][17]

Observation of the star in the infrared reveal an excess emission that suggests the presence of a circumstellar debris disk of orbiting dust,[15] much like those discovered around Fomalhaut and Vega. The mean temperature of this disk is 120 K,[17] indicating that it is centered at a radius of 47 AU from the host star.[15] The dust has an estimated mass of about 0.27% the mass of the Earth.[17]

Beta Ursae Majoris is one of five stars in the Big Dipper that form a part of a loose open cluster called the Ursa Major moving group, sharing the same region of space and not just the same patch of sky from Earth's perspective. This group has an estimated age of about 500 (± 100) million years. As the members of this group share a common origin and motion through space, this yields an estimate for the age of Beta Ursae Majoris.[18] Two stars are known to be located in relatively close proximity: 37 Ursae Majoris at Script error: No such module "convert". and Gamma Ursae Majoris at Script error: No such module "convert".; much closer to each other than these stars are to the Earth.[19]

Nomenclature

β Ursae Majoris (Latinised to Beta Ursae Majoris) is the star's Bayer designation.

It bore the traditional name Merak derived from the Arabic المراق al-marāqq 'the loins' (of the bear).[8] In 2016, the International Astronomical Union organized a Working Group on Star Names (WGSN)[20] 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 Merak for this star.[21]

The Hindus called the star Pulaha, one of the Seven Rishis.[8]

In Chinese, Script error: No such module "Lang". (Script error: No such module "Lang".), meaning Northern Dipper, refers to an asterism equivalent to the Big Dipper. Consequently, the Chinese name for Beta Ursae Majoris itself is Script error: No such module "Lang". (Script error: No such module "Lang"., Template:Langx) and Script error: No such module "Lang". (Script error: No such module "Lang"., Template:Langx).[22]

In culture

USS Merak (1918) and USS Merak (AF-21) are both United States navy ships.

See also

References

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  1. ↑ a b c d e Script error: No such module "Citation/CS1".
  2. ↑ a b c d Script error: No such module "Citation/CS1".
  3. ↑ a b Script error: No such module "Citation/CS1".
  4. ↑ a b c Script error: No such module "Citation/CS1".
  5. ↑ Script error: No such module "citation/CS1".
  6. ↑ Script error: No such module "Citation/CS1".
  7. ↑ Script error: No such module "Citation/CS1".
  8. ↑ a b c Script error: No such module "Citation/CS1".
  9. ↑ Template:Cite simbad
  10. ↑ Script error: No such module "citation/CS1".
  11. ↑ Script error: No such module "citation/CS1".
  12. ↑ Script error: No such module "Citation/CS1".
  13. ↑ Script error: No such module "Citation/CS1".
  14. ↑ Script error: No such module "Citation/CS1".
  15. ↑ a b c d Script error: No such module "Citation/CS1".
  16. ↑ Script error: No such module "citation/CS1".
  17. ↑ a b c Script error: No such module "Citation/CS1".
  18. ↑ Script error: No such module "Citation/CS1".
  19. ↑ Script error: No such module "Citation/CS1".
  20. ↑ Script error: No such module "citation/CS1".
  21. ↑ Script error: No such module "citation/CS1".
  22. ↑ Template:In lang AEEA (Activities of Exhibition and Education in Astronomy) 天文教育資訊網 2006 年 6 月 15 日 Script error: No such module "webarchive".

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Template:Stars of Ursa Major Template:Portal bar

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