Pisces

Pisces is a large constellation, but one that falls somewhat outside the plane of the Milky Way Galaxy.

Derivation

Pisces seems to be one of the oldest constellations in the sky. The ancient Syrians saw this region as representing two fishes bound by a cord, one fleeing toward the western horizon and one fleeing northward. This peculiar image was adopted by the Egyptians, who saw the fish as swimming from Set, the evil brother of Osiris. The Greeks adapted the story again - for them, one fish was Aphrodite, the other her son Eros, and both were escaping the giant Typhon.

Stars

Despite its fame, its size, and its prominence as a zodiacal constellation, the stars of Pisces are largely disappointing. Alpha Piscium is a star otherwise known as Alrescha, 'the Cord', which represents the point where the two fishes' cords meet.

Alrescha is the not the brightest of Pisces' stars, though: that honour goes to Gamma Piscium, which lies in the westward 'fish'. This is an irregular hexagon of stars which, though dim, are recognisable by their characteristic shape. The northern fish is much less well defined, being a faint straggle of stars in the direction of Andromeda.

Pisces and the Ecliptic

The Ecliptic passes through Pisces for some 37° (about a tenth) of its length, though at one point it passes within less than 9 arc minutes of the neighbouring constellation Cetus. The Sun enters this constellation on 12 March each year, and remains within it for 37 days, crossing the border into Aries on 18 April.

These dates mean that the Vernal Equinox occurs while the Sun is within the boundaries of Pisces, on or about 20 March each year. The exact point in the sky where the Sun is located when this happens is, for historical reasons, termed the First Point of Aries. This point marks the Celestial Meridian (that is, zero hours right ascension), and is the starting point for the mapping of the Celestial Sphere.