• Meteorological spring starts on March 1 and is based on annual temperature cycles, while astronomical spring starts on March 20 and is based on the Earth’s position relative to the sun.
• The vernal equinox, which occurs at the start of astronomical spring, is when the sun’s rays equally shine on both of the Earth’s hemispheres.

Thursday marks the vernal equinox, or the first day of spring, in the northern hemisphere — even if the weather in Michigan doesn’t seem particularly “springy” this week.

While meteorological spring began on March 1, Thursday marks the astronomical spring, or the day the Earth’s tilt begins to bring the northern hemisphere closer to the sun.

The shift is called the vernal equinox, halfway between the winter and summer solstices when the Earth tilts one hemisphere the farthest from the sun.

Here’s what to know about spring.

When does spring start 2025?

Astronomical spring starts at 5:01 a.m. Thursday, March 20.

What is the vernal equinox?

There are only two times of the year when the Earth’s axis is tilted neither toward nor away from the sun, resulting in a “nearly” equal amount of daylight and darkness at all latitudes, the National Weather Service said.

The word equinox is derived from two Latin words — aequus (equal) and nox (night). At the equator, the sun is directly overhead at noon on these two equinoxes. 

On the equinox and for several days before and after the equinox, the length of day will range from about 12 hours, 6½ minutes at the equator, to 12 hours, 8 minutes at 30 degrees latitude, to 12 hours and 16 minutes at 60 degrees latitude, the NWS said.

What is the difference between meteorological spring and astronomical spring?

There are two starts to spring, and here’s why, according to NOAA:

• Meteorological spring: Meteorological seasons are broken down into groupings of three months in our civil calendar based on the annual temperature cycle. We generally think of winter as the coldest time of the year and summer as the warmest time of the year, with spring and fall being the transition seasons. In the southern hemisphere, the seasons are reversed where summer occurs when the South Pole is oriented towards the sun, and winter happens when the South Pole faces away.
• Astronomical spring: The Earth’s orbit forms the basis for the astronomical calendar in which seasons are defined by two solstices and two equinoxes. The Earth is tilted 23.5 degrees on its axis of rotation, and how the North Pole is oriented toward or away from the sun determines two of these astronomical dates. Exact timing for the astronomical spring and fall seasons are subject to change because the timing is dependent on the Earth’s rotation, NOAA said.

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