TAMPA, Fla. (WFLA) – Both the sunrise and sunset will occur at 7:39, just at different times of the day on Sunday, March 15.
The unique occurrence will amount to 11 hours, 59 minutes and 58 seconds of daylight.
However, the spring equinox (first day of spring) doesn’t occur until Thursday. According to timeanddate.com, the word equinox literally means equal night. This leads many to believe there is exactly 12 hours of daylight and 12 hours of darkness, but that’s not 100% correct.
By Thursday, the day of the equinox, sunrise occurs at 7:34 am and the sunset is a bit later at 7:40 pm leading to 12 hours, 6 minutes and 40 seconds of daylight.
The technical definitions of sunrise and sunset are to blame here. The equinox always lands on the day when the sun crosses the equator from the southern hemisphere to the northern hemisphere, marking the official start of astronomical spring at exactly that moment in time.
On the equinox, the geometric center of the sun is technically above the horizon for 12 hours.
However, sunrise is defined as when the top of the sun rises above the horizon, not when the center of the sun crosses it. Sunset is defined as when the top of the sun dips below the horizon.
It takes the whole sun about 6 minutes to completely rise above or dip below the horizon leading to the 6 minute difference in sunrise and sunset times on the equinox.
So, according to the definitions, March 15 has just about 12 hours of daylight, but the equinox has 12 hours of the sun’s center being above the horizon.
Astronomical spring starts Thursday but did you know that meteorological spring started March 1st? Click here to find out why.