Spring will arrive this year on March 20th. I can remember for the longest time spring would arrive on March 21st so why the change?

It’s not really a change because spring can fall on March 19th, 20th or 21st. It all depends on the vernal equinox.

The vernal equinox marks the moment the Sun crosses the celestial equator.

The celestial equator is an imaginary line in the sky above the Earth’s equator, from south to north.

When all that happens spring comes on one of those three days in March.

Spring is also when daytime and nighttime are equal, approximately 12 hours. Daylight will start to increase until the first day of summer. (June 21)

The official time for spring in 2018 is March 20th at 12:15 p.m.

According to nationaldaycalendar.com in 2019 and 2020 the spring equinox will occur on March 20th.