Transcription
The axis of the Earth is an imaginary line on which the Earth rotates. It links up the two poles. Both the axis and the Earth are tilted at an angle of twenty-three and a half degrees.
During a revolution, the tilting of the axis results in direct sunlight falling on different places during different seasons. This causes variations in the duration of days, nights, and seasons, as well as the relationship between the location of the overhead Sun and the seasons.
Similarly, the revolution of the Earth and the tilting of the axis results in different angles of the Sun during different periods. When the Sun is directly overhead, we call this the overhead Sun. At this time, the Earth's surface and the midday Sun form a 90-degree angle. Different locations of the overhead Sun result in variations in the amount of solar radiation received in different areas and at different periods.
**Spring Equinox**
On the 21st or 22nd of March, the overhead Sun is over the equator. The equator receives the largest amount of solar radiation at this time. The northern hemisphere is in the spring equinox, while the southern hemisphere is in the autumn equinox. The angle of the Sun decreases towards the poles. On this day, the two hemispheres receive a similar amount of solar radiation, and the length of day and night is the same at all places on the Earth.
After this day, it is spring in the northern hemisphere, where the day is longer than the night. In the southern hemisphere, it becomes autumn when the day is shorter than the night.
**Summer Solstice**
On the 21st or 22nd of June, the overhead Sun is over the Tropic of Cancer. It receives the largest amount of solar radiation at this time. The northern hemisphere is in the summer solstice, while the southern hemisphere is in the winter solstice. The angle of the Sun decreases towards the poles.
On this day, the length of daytime in the northern hemisphere is the longest of the year, while that of the southern hemisphere is the shortest. Additionally, there are 24 hours of daylight at the Arctic Circle and 24 hours of darkness at the Antarctic Circle.
**Autumn Equinox**
On the 22nd or 23rd of September, the overhead Sun is over the equator again. The equator receives the largest amount of solar radiation on this day. The northern hemisphere is in the autumn equinox, while the southern hemisphere is in the spring equinox. The angle of the Sun decreases towards the poles.
On this day, the two hemispheres receive a similar amount of solar radiation, and the length of day and night is the same at all places on the Earth. After this day, it is autumn in the northern hemisphere, where the day is shorter than the night. In the southern hemisphere, it becomes spring when the day is longer than the night.
**Winter Solstice**
On the 21st and 22nd of December, the overhead Sun is over the Tropic of Capricorn. It receives the largest amount of solar radiation on this day. The northern hemisphere is in the winter solstice, while the southern hemisphere is in the summer solstice. The angle of the Sun decreases towards the poles.
On this day, the length of daytime in the northern hemisphere is the shortest of the year, while that of the southern hemisphere is the longest. There are 24 hours of darkness at the Arctic Circle and 24 hours of daylight at the Antarctic Circle.