Season Calendar

About Season Calendar

This free season calendar calculator shows exact start and end dates for all four seasons based on astronomical equinoxes and solstices. Get accurate season information for both Northern and Southern hemispheres.

How are season dates calculated?

Season dates are calculated using astronomical algorithms based on Earth's position relative to the Sun:

Equinoxes - When day and night are approximately equal length (around March 20 and September 22).
Solstices - When the sun reaches its highest or lowest point in the sky (around June 21 and December 21).

These dates are calculated using Jean Meeus astronomical formulas which account for Earth's elliptical orbit and axial tilt. The calculations are accurate to within minutes of the actual astronomical events.

Why do seasons differ between hemispheres?

Seasons are opposite in the Northern and Southern hemispheres due to Earth's 23.5-degree axial tilt:

Northern Hemisphere:
- Spring: March Equinox to June Solstice
- Summer: June Solstice to September Equinox
- Autumn: September Equinox to December Solstice
- Winter: December Solstice to March Equinox

Southern Hemisphere (reversed):
- Autumn: March Equinox to June Solstice
- Winter: June Solstice to September Equinox
- Spring: September Equinox to December Solstice
- Summer: December Solstice to March Equinox

When it's summer in the Northern Hemisphere, it's winter in the Southern Hemisphere, and vice versa.

What is an equinox?

An equinox occurs twice a year when the Sun crosses the celestial equator, resulting in nearly equal day and night lengths everywhere on Earth.

Spring (Vernal) Equinox - Around March 20-21:
- Marks the start of spring in Northern Hemisphere
- Marks the start of autumn in Southern Hemisphere
- Sun rises exactly in the east and sets exactly in the west
- Day and night are approximately 12 hours each

Autumn (Autumnal) Equinox - Around September 22-23:
- Marks the start of autumn in Northern Hemisphere
- Marks the start of spring in Southern Hemisphere
- Equal day and night length worldwide

The word 'equinox' comes from Latin meaning 'equal night'.

What is a solstice?

A solstice occurs twice a year when the Sun reaches its highest or lowest point in the sky, resulting in the longest or shortest day of the year.

Summer Solstice - Around June 20-21:
- Longest day of the year in Northern Hemisphere
- Shortest day of the year in Southern Hemisphere
- Sun reaches its highest point in the sky
- Marks the start of summer in Northern Hemisphere

Winter Solstice - Around December 21-22:
- Shortest day of the year in Northern Hemisphere
- Longest day of the year in Southern Hemisphere
- Sun reaches its lowest point in the sky
- Marks the start of winter in Northern Hemisphere

The word 'solstice' comes from Latin meaning 'sun stands still' - the sun appears to pause at its highest or lowest point before reversing direction.

Why do equinox and solstice dates vary each year?

Equinox and solstice dates can vary by a day or two each year due to several factors:

1. Leap Years - Earth takes 365.25 days to orbit the Sun, not exactly 365 days. Leap years keep the calendar synchronized.

2. Earth's Elliptical Orbit - Earth's orbit is not a perfect circle, causing slight variations in orbital speed.

3. Gravitational Influences - The Moon and other planets exert gravitational forces that affect Earth's orbit.

4. Axial Precession - Earth's axis slowly wobbles over a 26,000-year cycle.

This calculator uses precise astronomical algorithms to determine the exact date and time for each year between 1900 and 2100.

Are these astronomical or meteorological seasons?

This calculator shows ASTRONOMICAL seasons, which are based on Earth's position relative to the Sun and the dates of equinoxes and solstices.

Astronomical Seasons:
- Based on astronomical events (equinoxes and solstices)
- Start dates vary by a day or two each year
- Seasons are different lengths (89-93 days)
- Used by astronomers and in almanacs

Meteorological Seasons (not used here):
- Based on temperature patterns
- Fixed dates: Mar 1, Jun 1, Sep 1, Dec 1
- All seasons exactly 3 months (90-92 days)
- Used by meteorologists for weather forecasting

Astronomical seasons better represent the Sun's position and are more scientifically accurate.

Why are seasons different lengths?

Seasons vary in length (typically 89-93 days) due to Earth's elliptical orbit around the Sun:

Kepler's Laws of Planetary Motion:
- Earth moves faster when closer to the Sun (perihelion in early January)
- Earth moves slower when farther from the Sun (aphelion in early July)

Typical Season Lengths (Northern Hemisphere):
- Spring: ~92.8 days
- Summer: ~93.6 days
- Autumn: ~89.8 days
- Winter: ~89.0 days

Summer is the longest season because Earth is farthest from the Sun and moves slowest during that period. Winter is the shortest because Earth is closest to the Sun and moves fastest.

Do all countries use the same season definitions?

No, different cultures and regions define seasons differently:

Astronomical Seasons (this calculator):
- Used in most Western countries
- Based on equinoxes and solstices
- 4 seasons of unequal length

Meteorological Seasons:
- Used for weather forecasting
- Fixed 3-month periods
- Simplifies climate statistics

Traditional/Cultural Seasons:
- Chinese calendar: 24 solar terms, 6 seasons
- Hindu calendar: 6 seasons
- Indigenous Australian: 6 seasons based on weather patterns
- Nordic countries: May recognize 8 seasons

Equatorial Regions:
- Often have only 2 seasons: wet and dry
- Traditional 4-season model doesn't apply

This calculator uses the astronomical definition recognized internationally.

What happens at the equator?

The equator experiences unique seasonal patterns:

Day Length:
- Approximately 12 hours of daylight year-round
- Very little variation between summer and winter
- No extreme seasonal day length changes

Temperature:
- Minimal temperature variation throughout the year
- Consistently warm/hot temperatures
- No traditional four seasons

Seasons:
- Typically divided into wet and dry seasons
- Based on rainfall patterns, not temperature
- Equinoxes (Sun directly overhead) occur twice yearly

While this calculator shows astronomical season dates for the equator, the traditional four-season model is less meaningful there. Climate and weather patterns are more relevant than astronomical seasons.

How accurate is this season calculator?

This calculator uses Jean Meeus astronomical algorithms, which provide extremely accurate results:

Accuracy Level:
- Equinox/solstice times accurate to within 1-2 minutes
- Valid for years 1900-2100
- Accounts for Earth's elliptical orbit
- Includes corrections for orbital perturbations

Limitations:
- Does not account for local timezone or daylight saving time
- Shows dates in the selected year only
- Does not include local weather patterns

For practical purposes (planning activities, understanding seasons), this level of accuracy is more than sufficient. The actual moment of an equinox or solstice is less important than understanding the general seasonal progression.

Can I use this for gardening and agriculture?

Yes, but with some considerations:

Useful For:
- Understanding general seasonal progression
- Planning spring planting around equinox dates
- Anticipating first/last frost periods
- Tracking daylight hours for plant growth

Additional Factors to Consider:
- Local climate and microclimate conditions
- USDA hardiness zone (for planting dates)
- Average last frost date in your area
- Soil temperature and conditions
- Historical weather patterns

Astronomical season dates are starting points, but local conditions vary significantly. A spring equinox in Alaska means very different weather than a spring equinox in Florida. Consult local agricultural extension services for specific planting recommendations.

Why do some cultures celebrate seasons on different dates?

Cultural season celebrations often differ from astronomical dates for historical and practical reasons:

Cross-Quarter Days (Celtic/Gaelic traditions):
- Imbolc (Feb 1) - Midpoint between winter solstice and spring equinox
- Beltane (May 1) - Midpoint between spring equinox and summer solstice
- Lughnasadh (Aug 1) - Midpoint between summer solstice and autumn equinox
- Samhain (Nov 1) - Midpoint between autumn equinox and winter solstice

East Asian Solar Terms:
- 24 divisions of the year, each ~15 days
- Include equinoxes and solstices plus additional markers
- Used in Chinese, Japanese, Korean, Vietnamese calendars

Meteorological Seasons:
- Begin on the 1st of March, June, September, December
- Easier for record-keeping and statistics

This calculator shows astronomical seasons, which are based on Earth's position relative to the Sun - the most scientifically accurate definition.