Gamma Draconis
Etamin, also Eltanin or Ettanin, is the proper name of the star γ Draconis (Gamma Draconis, short γ Dra ).
Etamin belongs to the spectral type K5 and has an apparent magnitude of 2.4 mag. Etamin is about 150 light years away.
The name etamin and its traditional variants Eltanin and Ettanin mean " sea monster " or " serpent " ( the Arabic name of the constellation ). Another name of etamin is Alnath and is identical in meaning with the name of β Tauri, El Nath (Arabic: "the end" ). Another name of etamin is Rastaban what الراس التنين is (ar -Ras at- Tinnin ) derived from the Arabic الراس التنين and about " the head of the serpent ( the dragon )" means.
Gamma Draconis is in the south of England at its upper culmination practically at its zenith, an observation so you can then neglect the refraction in the atmosphere. Twice attempts were made to determine to him the annual parallax. Robert Hooke had a telescope in the monument commemorating the Great Fire of London built for this purpose in 1666. The arrangement, however, was not mechanically stable enough. 1725 then repeated Samuel Molyneux and James Bradley these measurements. They found too large a proper motion transverse to the expected direction. 1727 Bradley then published the discovery of the aberration of starlight, proving for the first time the movement of the earth around the sun.
Credentials
- Robert Hooke: An attempt to prove the motion of the earth from observations made , London 1674
- James Bradley: A Letter from the Reverend Mr. James Bradley Savilian Professor of Astronomy at Oxford, and FRS to Dr.Edmond Halley astronomer. Reg & c. Giving an Account of a New Discovered Motion of the Fix'd Stars. Philosophical Transactions (1683-1775), Volume 35 ( 1727), pp. 637-661 ( full text )
- Individual star of the second magnitude
- Dragon ( constellation )