Today, September 23rd at 7:51am, Sun reached Zero declination, if we observe Sun’s position at Equator on this day, we will see Sun will be exactly overhead at noon. In coming days if we keep observing the Sun’s position we will notice that Sun is moving towards south with each passing day. Sun will reach southernmost point on December 21st. Sun reaching the Zero declination point is called Equinox. This happens twice in a year; first one will be on March 20/21 and second will be on September 23rd. From March, the Sun will be in northern hemisphere of the sky reaching northern most point on June 21st at 23.50and returning to Zero declination in September. From September Sun will be in Southern hemisphere of the sky reaching extreme south point of -23.50on December 21st , from December Sun will start moving towards north and reach Zero declination on March 21st . March Equinox is called Vernal Equinox and September Equinox is called Autumnal Equinox.