Seasons

Seasons are recurring annual changes in climate and daylight caused chiefly by a planet’s axial tilt as it orbits its star. Their timing and intensity vary with latitude and local geography.

Axial tilt: The angle between a body's rotational axis and the perpendicular to its orbital plane. Earth's tilted rotation axis changes each hemisphere's sunlight angle and day length through the year.
Latitude: The angular distance of a location north or south of the equator. Latitude determines how strongly the Sun's angle and daylight duration change across the year.
Phenology: The study of recurring biological events and their timing in relation to environmental conditions. Seasonal flowering, migration, and breeding are central observations in phenology.
Axial tilt versus orbital eccentricity: A comparison between a planet's axis inclination and the variation in its orbital distance from its star. Earth's tilt, not its changing distance from the Sun, is the main cause of the seasons.
Northern Hemisphere: The half of Earth north of the equator. Its summer and winter occur at opposite times from those in the Southern Hemisphere.
Earth's orbit: The path Earth follows around the Sun, completing one revolution in about 365.25 days. Earth's yearly motion carries each hemisphere through its seasonal cycle.
Day length: The time between sunrise and sunset at a particular place and date. Seasonal changes in daylight length alter the time available for solar heating.
Growing season: The period in a year when temperatures and other conditions permit plant growth. Its length links seasonal climate to crop choices and agricultural productivity.
Milankovitch cycles: Long-term variations in Earth's orbit and orientation that alter the distribution of sunlight over thousands of years. These cycles shape ice-age rhythms, unlike the annual seasonal cycle.
Southern Hemisphere: The half of Earth south of the equator. Its seasons are roughly opposite those of the Northern Hemisphere.

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