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Alkaidia
''Alkaidia'' is an extinct genus of sea stars which lived in the western Tethys Ocean from the Barremian to Cenomanian stages of the Cretaceous period. It was first described in 1998, and two species are currently assigned to it. The type species, ''A. sumralli'', is known from both complete and fragmentary specimens collected in Texas, and fossils of an earlier species, ''A. megaungula'', have been found in Morocco. Discovery and naming The fossilized remains of ''Alkaidia'' were first described by paleontologists Daniel B. Blake and Robert Reid, III in a 1998 publication describing some Albian-aged starfish fossils from north-central Texas. The authors determined that over 50 specimens (some complete and other fragmentary) originating from the Washita Group represented a new genus and species which they named ''Alkaidia sumralli''. The generic name references Alkaid, a star in the constellation Ursa Major, while the specific name honors Colin Sumrall, who discovered and prepa ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Alkaid
Alkaid , also called Eta Ursae Majoris ( Latinised from η Ursae Majoris, abbreviated Eta UMa, η UMa), is a star in the constellation of Ursa Major. It is the easternmost star in the Big Dipper (or Plough) asterism. However, unlike most stars of the Big Dipper, it is not a member of the Ursa Major moving group. With an apparent visual magnitude of +1.86, it is the third-brightest star in the constellation and one of the brightest stars in the night sky. Physical properties Alkaid is a 10-million-year-old B-type main sequence star with a stellar classification of B3 V. Since 1943, the spectrum of this star has served as one of the stable anchor points by which other stars are classified. It has six times the mass; 3.4 times the radius, and is radiating around 594 times as much energy as the Sun. Its outer atmosphere has an effective temperature of about 15,540 K, giving it the blue-white hue of a B-type star. This star is an X-ray emitter with ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |