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Ceginus, Haris, Gamma Boötis, 27 Boötis

Proper NamesSeginus, Ceginus, Haris
Bayer DesignationGamma Boötis
Flamsteed Number27 Boötis
HR (BSC)5435
Right Ascension14h 32m 5s
Declination+38° 18' 30"
Distance87 light years
27 parsecs
MagnitudeApparent: +3.0
Absolute: +0.9
Spectral ClassA7III white giant
Optimum VisibilityMay

A white star that forms the western shoulder of Boötes, the Herdsman of the northern sky, and part of the prominent asterism of the Kite. It lies eastward of the famous Plough or Big Dipper in the sky, and a line from the Plough's tip (the star Dubhe) through the end of its handle (Alkaid) points in the approximate direction of Seginus.

The name Seginus (sometimes spelt Ceginus) means 'reaper', comes from an old name for the entire constellation of Boötes. Confusingly, the name Ceginus is occasionally given to other stars in the same constellation, especially the fainter star to the north of Seginus more usually known as Asellus Primus or Theta Boötis. Seginus is also sometimes called Haris, meaning 'guardian', from the fuller Arabic name Al Haris al Sama, 'the guardian of the north'.

Seginus is a giant white star of the classification known as Delta Scuti variables, and indeed it is the brightest confirmed variable of this type in the skies of Earth.* Its luminosity shifts due to physical pulsations within the star, causing its magnitude to oscillate between +3.02 to +3.07 over a matter of hours. This pattern is due to feedback cycles of heating and cooling, which in turn affect the opacity of Seginus' plentiful helium. These processes follow a predictable relationship, making it possible to calculate the distance to the star with precision: Seginus lies 86.8 light years from the Solar System.

* Some stars brighter than Seginus are suspected to be Delta Scuti variables, notably Vega and Procyon, but the status of these stars has yet to be definitively confirmed.


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