Aah, spring … the moment arrives

At 7:44 a.m. today, most people may be too busy getting children off to school or getting ready for work to notice a celestial event: the change of season.

At precisely that moment, the center of the sun will stand directly over Earth's equator and winter will give way to spring in the Northern Hemisphere.

It's the equinox -- one of two days a year when the sun is above and below the horizon an equal number of hours. The word comes from the Latin meaning "equal night." It could just as easily be equal day.

"Back in the ancient times, it was the beginning of the year and a real big event," says Bob Hayward, an astronomer at the Pisgah Astronomical Research Institute in Rosman. "Everybody was interested in when the sun was returning from its southern journey."

Because of the tilt of the Earth's axis, the sun appears to come north of the equator after the equinox. The days will lengthen and darkness shorten until the summer solstice June 21, the longest day of the year in the Northern Hemisphere.