Short answers, pulled from the story.
The Earth experiences seasons because it leans at an angle of approximately 23.4 degrees, a tilt known as obliquity of the ecliptic. This axial tilt causes one hemisphere to tilt toward the Sun while the other tilts away as the planet revolves around the star.
The astronomical solstices and equinoxes fall on dates like March 20, June 21, September 22, and December 21, though these dates shift slightly every year. The period from the March equinox to the June solstice takes 92.75 days, while the period from the September equinox to the March equinox is only 88.99 days.
The hottest days of the year do not arrive when the Sun is highest in the sky due to a phenomenon known as seasonal lag. This delay occurs because the Earth's surface, particularly the oceans, absorbs solar energy and releases it slowly over time, delaying the peak temperature by up to seven weeks after the maximum insolation.
Ecologists have codified nature into six distinct phases called prevernal, vernal, estival, serotinal, autumnal, and hibernal seasons. These ecological seasons are not tied to fixed dates but to the observable activity of plants and animals, such as the swelling of deciduous tree buds in February or the hatching of birds in June.
In the tropics, the concept of four seasons dissolves into a binary struggle between water and drought dictated by the movement of the Intertropical Convergence Zone. This cycle creates monsoon seasons that dominate regions like India, Thailand, and parts of Australia, where the rainy season is often more significant than the temperature changes.
At the Arctic Circle, the polar day is a period in the summer when the Sun does not set, and the polar night is a period in the winter when the Sun does not rise. On Ellesmere Island, Canada, the Sun begins to peek above the horizon for minutes per day at the end of February and remains below the horizon until it rises again on the 27th of February.