Spring is almost here; At least officially. The vernal equinox falls on Tuesday, marking the beginning of the spring season for the Northern Hemisphere. So what does this really mean? Here’s what you need to know about how we divide the year by Earth’s orbit.

What is the equinox?

As the Earth rotates around the Sun, it does so at a certain angle. For most of the year, the Earth’s axis is tilted towards or away from the Sun. This means that solar heat and light fall unequally on the northern and southern halves of the planet. During the equinox, Earth’s axis and orbit align so that both hemispheres receive the same amount of sunlight.

The word equinox comes from two Latin words meaning equal and night. This is because day and night last nearly the same amount of time at the equinox, but you may get a few extra minutes depending on where you are on the planet.

In the Northern Hemisphere, spring or vernal equinox can occur between March 19 and 21, depending on the year. The autumn or autumnal equinox may fall between September 21 and 24.

What is the solstice?

Solstices mark the periods during the year when the Earth is most toward or away from the Sun. This means that the hemispheres receive very different amounts of sunlight and the days and nights are extremely unequal.

During the Northern Hemisphere summer solstice, the upper half of the Earth tilts toward the Sun, creating the longest day and shortest night of the year. This solstice falls on June 20-22.

Meanwhile, on the winter solstice, the northern hemisphere deviates from the sun, resulting in the shortest day and longest night of the year. The winter solstice falls on December 20-23.

What is the difference between meteorological and astronomical seasons?

These are just two different ways to divide the year. Meteorological seasons are determined by the weather. They divide the year into three-month seasons based on annual temperature cycles. According to this calendar, spring begins on March 1, summer begins on June 1, autumn begins on September 1, and winter begins on December 1.

Astronomical seasons depend on how the Earth revolves around the Sun. The equinox marks the beginning of spring and autumn. The solstice opens summer and winter.