description Etamin Overview
Etamin, also known as Gamma Draconis, is an orange giant star in the constellation Draco, approximately 154 light-years from Earth. It is the brightest star in Draco by apparent magnitude. Astronomer James Bradley made repeated observations of Etamin between 1725 and 1728 seeking to measure its parallax, and from this data he discovered stellar aberration, evidence of Earth's orbital motion. The star has a visual companion and lies close to the path of the north celestial pole's precessional circuit.
help Etamin FAQ
Why did James Bradley observe Etamin?
Bradley and Samuel Molyneux observed Gamma Draconis while trying to detect annual stellar parallax. Its path almost directly over London made it well suited to measurements with their nearly vertical telescope.
What did observations of Etamin reveal instead of parallax?
Bradley found an annual displacement that could not be explained as the expected parallax. He recognized it as stellar aberration, an apparent shift caused by Earth's orbital motion combined with the finite speed of light.
Is Etamin the same star as Eltanin?
Yes, Etamin and Eltanin are variant names for Gamma Draconis. The International Astronomical Union's standardized form is Eltanin, although Etamin remains common in historical writing.
How can Etamin be Draco's brightest star when it is called Gamma Draconis?
Bayer letters do not always follow exact apparent brightness, so the gamma designation does not mean the star ranks third. Eltanin is brighter in Earth's sky than Alpha Draconis, better known as Thuban.
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