Sunset at the Portara . ... Credit Copyright: Anthony Ayiomamitis ( TWAN ) Explanation: Today, the Sun crosses the celestial equator heading north at 11:44 UT . Known as an equinox, this astronomical event marks the first day of spring in the northern hemisphere and autumn in the south. ... With the Sun on the celestial equator, Earth dwellers will experience nearly 12 hours of daylight and 12 hours of darkness. ... NASA Web Site Statements, Warnings, and Disclaimers . ...