Seasons Calculator

Astronomical seasons are based on Earth's position relative to the Sun — specifically the equinoxes and solstices — and vary slightly in date each year. Meteorological seasons are fixed to calendar months (e.g. spring = March, April, May in the Northern Hemisphere) and are used by weather services for consistency in climate records.

Earth's orbit around the Sun takes approximately 365.25 days, which is why we add a leap year every four years. This fractional day causes the exact moment of each equinox and solstice to shift slightly from year to year, typically varying by a day or two within a fixed range.

In the Northern Hemisphere, spring begins at the March (vernal) equinox, which typically falls between March 19 and March 21. This is the moment when the Sun crosses the celestial equator heading northward and day and night are approximately equal in length.

Yes. When it is summer in the Northern Hemisphere, it is winter in the Southern Hemisphere, and vice versa. The solstices and equinoxes occur at the same moment globally, but the season names are flipped — so the June solstice marks the start of winter in the Southern Hemisphere.

In the Northern Hemisphere, summer is the longest season at approximately 93–94 days, because Earth is near its aphelion (farthest point from the Sun) in July and moves more slowly. Winter is the shortest season at around 89 days, since Earth moves fastest near perihelion in January.

An equinox occurs twice a year (around March 20 and September 22) when the Sun is directly above the equator, resulting in roughly equal day and night lengths worldwide. A solstice occurs twice a year (around June 21 and December 21) and marks the point when the Sun reaches its northernmost or southernmost position, giving the longest or shortest day of the year.

This calculator uses the Jean Meeus algorithmic approximation for equinox and solstice dates, which is accurate to within a few minutes for years close to the present. For historical or far-future years, small cumulative errors may occur due to gravitational perturbations and Earth's axial precession not being fully modeled.

In many cultures, astronomical season start dates align with festivals and cultural events — for example, the spring equinox aligns with Persian New Year (Nowruz) and the winter solstice with celebrations like Dongzhi in East Asia. However, official public holidays are typically set by fixed calendar dates rather than the exact astronomical moment.