The literary meaning of Equinox is equal day and night. when the sun is in the intersecting point of the celestial Equator and the Ecliptic , where Arles commences and Pisces ends and the point of intersection is at the end of Virgo and the beginning of Libra, then the days and night are equal all over the world. this phenomenon occurs only twice in a year, that is on 21st March and 23rd September.
Astrology sign Mesh (Aries) and Tula (Libra) are hence the two equinoctial signs. Mesh (Aries) is the vernal equinoctial sign and Tula (Libra)is known as autumnal equinoctial sign.