April is the fourth month of the year in the Gregorian Calendar, and one of four months with the length of 30 days. The month of April begins (astrologically) with the sun in the sign of Aries and ends in the sign of Taurus. Astronomically speaking, the sun begins in the constellation of Pisces and ends in the constellation of Aries. The signs of the zodiac do not necessarily coincide with the actual constellations for which they are named. The precession of the equinoxes, a phenomenon discovered c. 130 BC by Hipparchus and known to Ptolemy, results in a shift between the two systems of about one degree every 70 years. The vernal equinox lay near the beginning of the Aries constellation around 500 BC, consistent with a 

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ian origin of the system.