For some reason I grew up thinking the equinox was always the 21st because the 21st was marked the first day of Spring on the calendar. Yes, the 21st is the first full day of Spring, but the actual start of Spring differs each year.
The first day of Spring can be March, 19th, 20th or 21st depending on the Vernal (Spring) Equinox. Relative to the earth this is the moment the Sun crosses the equator line, heading north. It's then we begin to feel some warm rays in the northern hemisphere and enjoy the "tilt".
The exact start of the Vernal Equinox is one time on earth and recorded as different times on different time zones. It also changes a little from year to year. This year it was Saturday March 20th at 5:37 AM Ney York Time. That is 6:37 PM Sunday March 21st in Seoul.
Some may totally disagree with this and tell me the world is flat, but one thing everyone can agree on is that the weather is changing in many places. North of the equator it is beginning to be warm. We see insects coming out that were dormant all winter. We see tadpoles and we feel the warmth of the sun again. Because of this many songs were written about spring. Here are a few I enjoy.
We are made of dreams and bones
A prophetic look at spring
Spring isn't Spring without frogs
Cover photo:
https://pixabay.com/photos/woman-field-sunlight-fashion-hat-1509956/