Messier 21

 Nota: Para fuzil de assalto, veja M21 (fuzil).
Messier 21
Messier 21
Messier 21
Descoberto por Charles Messier
Data 1764
Dados observacionais (J2000)
Constelação Sagittarius
Asc. reta 18h 04m 36,00s
Declinação -22° 30′ 00,0″
Distância 4 250 anos-luz (1,3 kpc)
Magnit. apar. 6,5
Dimensões 13',0
Características físicas
Idade estimada 4,6 milhões de anos
Outras denominações NGC 6531
Messier 21

Messier 21 (NGC 6531) é um aglomerado estelar aberto localizado na constelação de Sagitário. Foi descoberto pelo francês Charles Messier em 5 de junho de 1764.

Messier 21 é um aglomerado relativamente jovem de estrelas, com meros 4,6 milhões de anos, e situa-se aproximadamente 4 250 anos-luz em relação à Terra. É altamente denso mas contém apenas 57 estrelas Algumas estrelas gigantes azuis foram identificadas no aglomerado, mas a maior parte de suas estrelas são pequenas. Com uma magnitude aparente de 6,5, Messier 21 não é visível a olho nu, embora seja facilmente visível com bons binóculos em noite com boas condições de visibilidade.

Descoberta e visualização

O aglomerado aberto é uma das descobertas originais do astrônomo francês Charles Messier, que o catalogou em 5 de junho de 1764.[1]

Características

Messier 21, projeto 2MASS

É um aglomerado aberto que exibe uma forte concentração estelar em seu núcleo. Foi classificado por Woldermar Götz como pertencente à classe I,3,r, segundo a classificação de aglomerados abertos de Robert Julius Trumpler, onde a classe I refere-se aos aglomerados mais densos e a classe IV aos menos densos; a classe 1 aos aglomerados com pouca diferença de brilho entre seus componentes e a classe 3 aos que tem grande diferença de brilho; e a classe p aos aglomerados pobres em estrelas, m para aglomerados com a quantidade de estrelas dentro da média e r para os ricos em estrelas. Trumpler havia classificado anteriormente o aglomerado como I,3,p. De acordo com Sotirios Svolopoulos, o aglomerado contém 57 estrelas, sendo as mais brilhantes pertencentes à classe espectral B0. Com base nisso, estima-se que o objeto tenha apenas 4,6 milhões de anos e que pertença à associação estelar OB1, segundo o Sky Catalogue 2000.0.[1]

As estimativas de sua distância em relação à Terra são discordantes, variam entre 2 200, segundo Robert Burnham Jr., a 4 250 anos-luz, segundo o Sky Catalogue 2000.0 e Kenneth Glyn Jones. John Mallas e Evered Kreimer estimaram sua distância em 3 000 anos-luz.[1]

Galeria

  • Messier 21, José Carlos Castro
    Messier 21, José Carlos Castro
  • Messier 21, Ole Nielsen
    Messier 21, Ole Nielsen

Ver também

Ligações externas

Referências

  1. ↑ a b c Hartmut Frommert e Christine Kronberg (21 de agosto de 2007). «Messier Object 21» (em inglês). SEDS. Consultado em 28 de maio de 2012 
   NGC 6529  •  NGC 6530  •  NGC 6531  •  NGC 6532  •  NGC 6533   

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