What happens during an equinox? And who even decides which day is the first day of spring? If you don't know the answers to these questions, don't feel embarrassed. You're in good company.

Spring is here — officially, at least. The vernal equinox arrives on Thursday, marking the start of the spring season for the Northern Hemisphere and the fall in the Southern Hemisphere.

What Happens at the Spring Equinox? As a result of the sun crossing the equator and being located more north in the sky, the Northern Hemisphere tilts more toward the sun.