Astronomical spring begins late Tuesday night

Astronomical spring begins at 11:06 Tuesday night, It's the Vernal Equinox. It differs from Meteorological spring and starts nearly three weeks later. -- Rich Segal

By definition, astronomical spring and meteorological spring happen at different times. Meteorological spring starts March 1st and ends May 31st every year. It is based on the annual temperature cycle. It starts about 20 days before astronomical spring. The more definitive timeline of meteorological spring also helps with record keeping as data and statistics can be collected more easily.

Astronomical spring is based on the where the Earth is relative to the Sun. The start date is dependent on when the Sun reaches its highest point over the Equator before heading to the northern hemisphere. By contrast, astronomical fall begins the sun's heading to the southern hemisphere.

The length of astronomical spring can vary from 89 to 93 days versus the more definitive 92 days of March, April, and May.

It's known as the spring, or the vernal equinox. The equinox occurs twice a year. Most refer to the one in spring as the vernal equinox while the one in September is commonly called the autumnal equinox. In either case, it's when the Sun is exactly above the Equator allowing day and night to be of equal length.

What's even more characteristic of the two equinoxes is that it is on both days where the sun rises exactly in the east and sets exactly in the west.

Vernal means relating to or occurring in spring. Equinox means the date or time when the Sun crosses the Equator.

While the definition of the vernal equinox means that daylight and nighttime are the same length, a look at the sunrise and sunset times tell a little bit of a different story.

This upcoming vernal equinox will happen at 11:06 p.m. Tuesday. The sunrise and sunset times for Wednesday (the first full day of astronomical spring) shows 12 hours and 8 minutes of daylight and 11 hours and 52 minutes of nighttime, a difference of 16 minutes.

The day where daytime and nighttime were about equal was March 15th when the two were separated by two minutes.

There is one more tidbit regarding the start of 2024 astronomical spring. In the past the first day has fallen around March 20th or 21st, This year, it's starting on March 19th, late in the night as it may be. Why?

It's because we have that extra day this year, the one on February 29th. 2024 is a Leap Year. There is that extra day added to the calendar that leads to the earlier start to spring.

In 2020, the beginning to astronomical spring also occurred late in the night of March 19th.

Astronomical summer, or the Summer Solstice, begins on June 20th at 3:50 p.m. By definition, it's the longest day of the year.