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Svalocin, Alpha Delphini, 9 Delphini

Proper NameSualocin (sometimes spelt Svalocin)
Bayer DesignationAlpha Delphini
Flamsteed Number9 Delphini
HR (BSC)7906
Right Ascension20h 39m 38s
Declination+15° 54' 43"
Distance254 light years
78 parsecs
MagnitudeApparent: +3.8
Absolute: -0.7
Spectral ClassB9IV blue subgiant
Optimum VisibilityAugust
NotesSualocin is a binary system comprised of a blue star and a much fainter white star that orbit one another over a period of some seventeen years. Five further stars lie in close proximity to Sualocin in Earth's sky, but are considered to be optical companions only, and not physically associated with the main binary system.

A blue fourth-magnitude star in the constellation of Delphinus the Dolphin, and one of the four stars that together make up the small diamond-shaped formation known as Job's Coffin. Alpha Delphini is in fact very slightly fainter than the Beta star of the constellation, commonly called Rotanev, which lies to the south and west (though neither of these stars exceed magnitude +3.5).

Sualocin represents a binary system dominated by a blue main sequence star (or possibly a subgiant), formally designated Alpha Delphini Aa. This primary star has a much fainter and less massive companion orbiting at a distance of some twelve AU, probably belonging to the white A-type spectral class. The system also has five other companions, designated Alpha Delphini B, C, and so on, but these merely lie on the same line of sight from Earth, and are not part of the Sualocin system itself.

Imagery provided by Aladin sky atlas

The name Sualocin has a curious origin, which links it with its near-neighbour Rotanev. Both these names were added during the compilation of the Palermo Star Atlas in the nineteenth century by one Niccolò Cacciatore, who was assistant to Giuseppe Piazzi, the compiler of the atlas. Cacciatore Latinised his name to Nicolaus Venator (which would be 'Nicholas Hunter' in English), and then reversed it to produce Rotanev and Sualocin, which he inserted into the atlas as if they were traditional star-names. Though introduced in a rather informal way, the names entered common use, and are now officially recognised as belonging to the two brightest stars in Delphinus.


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