Spring started a little earlier than usual this year. 

Tuesday, March 19 at 11:06 EDT marked the vernal equinox for the Northern Hemisphere, when the sun was directly over the equator and its energy was in balance between the Northern and Southern Hemispheres, according to the National Weather Service.

Most years, the season typically changes on March 20 or 21. So, why did spring start a few hours earlier in 2024?

The reason the first day of spring was March 19 was because 2024 is a leap year. Leap years are caused by Earth's rotation. A year is 365 days, but technically it takes the Earth slightly longer to orbit around the sun.

The Earth takes 365 days, 5 hours, 48 minutes and 46 seconds — or 365.2422 days — to fully orbit the sun, according to NASA.  Those extra hours are eliminated from the calendar most years. But every four years, an extra day is added to February so the calendar and seasons don't get out of sync. If this didn't happen, the extra hours would add up over time and seasons would start to change.