"... In the sky, Perseus lies next to his beloved Andromeda. Nearby are her parents Cepheus and Cassiopeia, as well as the monster, Cetus, to which she was sacrificed. Pegasus the winged horse completes the tableau. Perseus himself is shown holding the Gorgon’s head.

The star that Ptolemy called ‘the bright one in the Gorgon head’ is Beta Persei, named Algol from the Arabic ra’s al-ghul meaning ‘the demon’s head’. (As an aside, al-ghul is also the origin of our word alcohol - quite literally ‘the demon drink’.) Algol is the type of star known as an eclipsing binary, consisting of two close stars that orbit each other, in this case every 2.9 days ..." (ianridpath.com)

The helmet of Perseus is a cap Sign and the smiling face mask of Medusa is a cup Sign. Perseus is the high dry summer hero and Medusa the low wet 'water bucket'. But I think her face cannot be seen because it is turned in the opposite direction, away from us, and therefore a mask is needed.

2.9 equals 29 / 10 and the 29th night is a dark night, a night of Mercury.

South of the equator - or where the river ends in the north (Egypt) - the 'demon' ought to be a sign of summer instead of a sign of winter.