Many people believe that summer occurs when the Earth is closer to the Sun. This is not true. In fact, when the Northern Hemisphere experiences summer, the Southern Hemisphere experiences winter, and vice versa. So what causes the four seasons? Let’s learn.
The seasons on Earth (or any other planet) occur due to its axial tilt. Earth’s axis is an imaginary line passing through the geographic North and South Poles, around which the planet rotates. This axis is tilted at an angle of about 23.5° with respect to the perpendicular to its orbital plane.
When the North Pole tilts toward the Sun, the Northern Hemisphere experiences summer because it receives more direct sunlight. At the same time, the Southern Hemisphere experiences winter since it receives less direct sunlight.
(Fun fact: Earth is farther from the Sun during the Northern Hemisphere’s summer)
The four seasons on Earth
Summer
During summer, temperatures rise and the days become longer. Mid-summer in the Northern Hemisphere occurs when the North Pole has the maximum tilt towards the Sun. At the same time, the Southern Hemisphere experiences mid-winter.
Mid-summer (summer solstice) in Northern Hemisphere = Mid-winter (winter solstice) in Southern Hemisphere = around 21 June
Winter
During winter, temperatures drop and the days become shorter.
Mid-winter (winter solstice) in Northern Hemisphere = Mid-summer (summer solstice) in Southern Hemisphere = around 21 December
Spring
Spring is the season when flowers begin to blossom. It is essentially the transition period from winter to summer.
Autumn
Autumn is the season when trees shed their leaves. It is essentially the transition period from summer to winter.
(Also read: Why is the South Pole colder than the North Pole?)
Equinox and solstice
An equinox is the time of year when day and night are nearly equal in length. It happens twice a year, once in spring and once in autumn. In the Northern Hemisphere, the spring equinox (which is the autumn equinox in the Southern Hemisphere) occurs around 20 March. The autumn equinox in the Northern Hemisphere (and spring equinox in the Southern Hemisphere) occurs around 22 September.
A solstice is the time of year when the Earth’s axis is tilted most strongly toward or away from the Sun. This results in the longest and shortest days of the year. In the Northern Hemisphere, the summer solstice (also the winter solstice in the Southern Hemisphere) occurs around 21 June. The winter solstice in the Northern Hemisphere (and summer solstice in the Southern Hemisphere) occurs around 21 December.
Seasons at the poles
The Poles experience extremely cold winters and cool summers. In winter, the Sun does not rise at all, resulting in 24 hours of darkness. In contrast, during summer, the Sun does not set, and there is continuous daylight for 24 hours.
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