Riding the wave

The Swan

The constellation of the Swan (Cygnus in Latin), was introduced in the northern sky by Ptolemy. It was named after the son of Sthenelus, king of Liguria - mentioned by Virgil in the tenth book of the Aeneid - who was changed into a swan by Apollo while mourning the death of his friend Phaeton.

It entirely spans in the Milky Way between Aquila/the Eagle and the Lyra, and is clearly visible to the naked eye for its five beautiful stars in the shape of a Latin cross (four at the ends and one in the middle), so that it is also known as the "Cross of the Swan".

The star at the NE end of the cross is Deneb (a Cygni) while the one at the lower end is Albireo (Cygni b), one of the most beautiful binary stars in the sky.

Very well known is the 61Cygni, because it is one of the stars closest to us (11 light-years). Also, it is the first star of which the distance from the earth was measured (FW Bessel, 1838).

In 1943 A. Strand recognized (by calculation) the presence of a dark satellite 61Cygni, of exceptionally small mass, so as to be considered a planet, which is the first extrasolar planet to be discovered.