Seasons Calculator
Find the exact dates of solstices and equinoxes for any year and hemisphere. Enter values for instant results with step-by-step formulas.
Reviewed by Abdullah, Technical Content Specialist
Formula
Seasons are defined by solstices (max/min solar declination) and equinoxes (0 declination)
Solstice and equinox dates are calculated using the Meeus algorithm, which approximates the Julian Ephemeris Day when the Sun reaches specific ecliptic longitudes: 0 degrees (March equinox), 90 degrees (June solstice), 180 degrees (September equinox), and 270 degrees (December solstice). The calculation accounts for the elliptical nature of Earth orbit.
Worked Examples
Example 1: 2024 Solstices and Equinoxes (Northern Hemisphere)
Problem:Find the dates of all four seasonal markers for 2024 in the Northern Hemisphere.
Solution:Using the Meeus algorithm for approximate solstice/equinox dates:\nVernal Equinox: March 20, 2024 (Spring begins)\nSummer Solstice: June 20, 2024 (Longest day, Summer begins)\nAutumnal Equinox: September 22, 2024 (Autumn begins)\nWinter Solstice: December 21, 2024 (Shortest day, Winter begins)
Result:Spring: Mar 20 | Summer: Jun 20 | Autumn: Sep 22 | Winter: Dec 21, 2024
Example 2: Season Duration Calculation
Problem:Calculate how many days each season lasts in the Northern Hemisphere for 2024.
Solution:Spring: March 20 to June 20 = 92 days\nSummer: June 20 to September 22 = 94 days\nAutumn: September 22 to December 21 = 90 days\nWinter: December 21 to ~March 20, 2025 = ~89 days\nTotal: 365 days
Result:Summer is the longest season (94 days), Winter is the shortest (89 days)
Frequently Asked Questions
What causes the seasons on Earth?
The seasons are caused by the tilt of Earth rotational axis, which is inclined at approximately 23.44 degrees relative to the plane of its orbit around the Sun. As Earth orbits the Sun over the course of a year, this axial tilt causes different hemispheres to receive varying amounts of direct sunlight. During the Northern Hemisphere summer, the North Pole tilts toward the Sun, resulting in longer days, more direct sunlight, and warmer temperatures. Six months later, the North Pole tilts away from the Sun, producing winter conditions. Contrary to common misconception, the seasons are not caused by Earth varying distance from the Sun. In fact, Earth is closest to the Sun (perihelion) in early January during Northern Hemisphere winter, and farthest (aphelion) in early July during Northern Hemisphere summer.
Why are the four seasons not equal in length?
The four astronomical seasons are not equal in length because Earth orbit around the Sun is slightly elliptical rather than perfectly circular, and Earth moves faster when it is closer to the Sun (perihelion, early January) and slower when it is farther away (aphelion, early July), following Kepler second law of planetary motion. In the Northern Hemisphere, summer (June solstice to September equinox) is the longest season at approximately 93.6 days, while winter (December solstice to March equinox) is the shortest at approximately 89.0 days. Spring lasts about 92.8 days and autumn about 89.8 days. The faster orbital speed during perihelion causes the Northern Hemisphere winter to be shorter, which is why the Southern Hemisphere winter (which occurs during aphelion) is slightly longer than the Northern Hemisphere winter.
How do the seasons differ between the Northern and Southern Hemispheres?
The seasons in the Northern and Southern Hemispheres are exactly opposite: when it is summer in the Northern Hemisphere, it is winter in the Southern Hemisphere, and vice versa. The March equinox marks the beginning of spring in the North and autumn in the South, while the September equinox marks autumn in the North and spring in the South. The June solstice is the summer solstice in the North but the winter solstice in the South. This reversal occurs because when the North Pole tilts toward the Sun, the South Pole simultaneously tilts away. The Southern Hemisphere experiences slightly more intense summers than the Northern Hemisphere because the December solstice (Southern summer) occurs near perihelion when Earth is closest to the Sun, though this effect is moderated by the larger ocean area in the Southern Hemisphere absorbing more heat.
What is the difference between astronomical and meteorological seasons?
Astronomical seasons are defined by the positions of the Earth relative to the Sun, beginning at the solstices and equinoxes. These dates vary slightly each year and do not align with calendar month boundaries. Meteorological seasons, used primarily by weather agencies and climate scientists, divide the year into four three-month periods based on the annual temperature cycle: Spring is March through May, Summer is June through August, Autumn is September through November, and Winter is December through February in the Northern Hemisphere. Meteorological seasons provide a more consistent framework for comparing seasonal climate data across years because they align with complete calendar months. The astronomical and meteorological definitions typically differ by about 20 days; for example, astronomical summer begins around June 21, but meteorological summer begins on June 1.
References
Reviewed by Abdullah, Technical Content Specialist · Editorial policy