The astronomical spring began at 12:28 on 20th of March 2017.
The spring (vernal) equinox in the Northern Hemisphere marks the First Spring Day. The night and day are nearly exactly the same length – 12 hours. After that, the days are getting longer.
The period from the start of the astronomical spring to the start of the next astronomical spring is one tropical year and equals 365, 24219 days.
The world’s mostly used calendar system is based on the so-called „Gregorian calendar“. It is a solar calendar based on a 365-day common year divided into 12 months of irregular lengths. Nearly every four years, there is is a leap year which has 366 days to keep our modern day Gregorian calendar in alignment with the Earth’s revolutions around the sun.
The Equinox can happen on March 19, 20, or 21. Many cultures accept 21st of March as the day of March equinox. In the 21st century, a March 21 Equinox happened only twice – in 2003 and 2007.