The Zodiac symbols known to have been in use by the Roman era based on concepts inherited by Hellenistic astronomy from Babylonian astronomy of the Chaldean period (mid-1st millennium BC), which, in turn, derived from an earlier system of lists of stars along the ecliptic. The construction of the zodiac is described in Ptolemy's Almagest (2nd century AD). The division of the ecliptic into the zodiacal signs originates in Babylonian ("Chaldean") astronomy during the first half of the 1st millennium BC, likely during Median/"Neo-Babylonian" times (7th century BC). The classical zodiac is a modification of the MUL.APIN catalogue, which was compiled around 1000 BC. Some of the constellations can be traced even further back, to Bronze Age (Old Babylonian) sources. Aquarius (♒) is the eleventh astrological sign in the Zodiac, originating from the constellation Aquarius. Under the tropical zodiac, the sun is in Aquarius typically between January 20 to February 19, while under the Sidereal Zodiac, the sun is in Aquarius from approximately February 15 to March 14, depending on leap year.
