Since the Earth's equator is lined up with the center of the Sun, the equinox turns into the day when people all around the globe experience day and night of equivalent length, or around 12 hours each. The equinox occurs at 5:58pm EDT and that's the precise minute the sun is directly over earth's equator.
21st full moon will be the first full moon of spring in the Northern Hemisphere (and the first full moon of autumn for the Southern Hemisphere). Interesting tidbit, the word "equinox" is derived from two Latin words - aequus, meaning "equal" and nox, meaning "night".
Another reason why the equinoxes don't bring equal amounts of day and night time is due to the refraction of light. This equinox extends to USA, Central America, Canada, Europe, Asia and northern Africa. The Iranian tradition was passed onto Central Asians - Kazakhs, Uzbeks, Uighurs - who celebrate the new year on this day called Nauryz.
Why is it special this year?
The third, happening tonight, will be the final supermoon of 2019. Heralding the milder temperatures and possibly wilder weather is the first phase of a full moon this year.
A full moon and the spring equinox haven't occurred this closely since 2000, and won't sync up again until March of 2030. There was a lunar eclipse in January and the largest supermoon of the year was in February. Supermoons make the moon appear a little brighter and closer than normal.