Notes-Class-7-Geography-Chapter-8-How Seasons Occur-Part 2-Maharashtra Board

Apparent movement of the sun :

Annual apparent (South-North) movement of the sun :

• Every day, the position of the sun at sunrise appears to vary on the horizon. Its position appears to shift north and south over the course of a year. The sun, on the other hand, does not move.
• As a result, this movement of the sun towards the north or south over the course of a year is referred to as the apparent movement of the sun.
• The position of the rising sun appears to move towards the south in the period from 21^st June to 22^nd December. This period is called Dakshinayan.
• The position of the rising sun appears to move towards the north in the period from 22^nd December to 21^st June. This period is called Uttarayan.

Diurnal apparent (East-West) movement of the sun :

• Every day, from sunrise to sunset the sun appears to move from the east to the west.
• This apparent movement of the sun is called diurnal apparent movement of the sun.

Causes of apparent movements of the sun :

• The annual apparent (South-North) movement of the sun is related to the revolution of the earth and the tilt of the earth’s axis.
• The diurnal apparent (East-West) movement of the sun is related to the rotation of the earth.

Perihelion and aphelion positions of the earth :

(i) Perihelion position :

• During its revolution, the earth’s distance from the sun is at its minimum in the first week of January. This is called perihelion position of the earth.
• In this position, the southern end of the axis is towards the sun.

(ii) Aphelion position :

• During its revolution, the earth’s distance from the sun is at its maximum in the first week of July. This is called aphelion position of the earth. In this position, the northern end of the axis is towards the sun.

Occurrence of seasons :

• Seasons occur due to the revolution of the earth as well as due to the tilt of its axis of rotation.
• Seasons occur only with reference to the northern and the southern hemisphere.

Perpendicular sunrays in the region from the Equator to Tropic of Cancer and from the Equator to the Tropic of Capricorn :

• The sunrays are perpendicular at the Equator on 22^nd March and 23^rd September. After 22^nd March, other parallels between the Equator and the Tropic of Cancer in the northern hemisphere and after 23^rd September, other parallels between the Equator and the Tropic of Capricorn start receiving perpendicular sunrays sequentially.
• When any one of the poles inclines the most towards the sun, 23° 30’ parallel of that hemisphere receives perpendicular sunrays.
• Only on 21^st June and 22^nd December, the sunrays become perpendicular on the
• Tropic of Cancer and the Tropic of Capricorn respectively. These two days are called Solstice days.
• Sunrays are never perpendicular on any of the parallels between the Tropic of Cancer and the North Pole or between the Tropic of Capricorn and the South Pole.

Longest day and shortest day in the northern hemisphere and southern hemisphere :

• 21^st June is the longest day (shortest night) in the northern hemisphere. The same is the shortest day (longest night) in the southern hemisphere.
• 22^nd December is the longest day (shortest night) in the southern hemisphere. The same is the shortest day (longest night) in the northern hemisphere.

Daytime and nighttime in the region from the Arctic Circle to the North Pole :

• In the region from the Arctic Circle to the North Pole, the sun remains visible for 24 hours or longer.
• At the North Pole, the sun is visible in the sky from 22^nd March to 23^rd September.

Daytime and nighttime in the region from the Antarctic Circle to the South Pole :

• In the region from the Antarctic Circle to the South Pole, the sun remains visible for 24 hours or longer.
• At the South Pole, the sun is visible in the sky from 23^rd September to 21^st March.

Seasons :

• Seasons have been decided on the basis of the duration of the sunlight, equinoxes and solstices.
• The Equatorial Region does not experience any change of season. Hence the climate in that region does not change at all in the year.
• In the places beyond the Equatorial Region in either hemispheres, summers or winters are experienced one after the other, within a year.
• The occurrence of seasons one after the other in a year leads to the ‘cycle of seasons’. Generally, there are two seasons, summer and winter, on the earth. However, in some places, seasons are taken to be four in all.
• The change in the atmosphere, vapour in the air, the Wind and precipitation also influence the seasons. Continuous occurrence of rain in a specific period give rise to an additional season besides summer and winter.
• Due to the local conditions, seasons other than summer and winter are seen to occur in different parts.

The cycle of season and the living word :

• The seasons would not have occurred if the earth's axis had not been inclined. The tilt of the axis is responsible for the occurrence of seasons, change, and diversity on Earth.
• The seasonal cycle promotes biodiversity on the planet. For example, in the hemispheres between 66° 30' and 90°, even the smallest amount of sunshine available for a portion of the year gives rise to particular flora and fauna.
• Birds such as penguins, fish such as seals, and animals such as walruses can be found in the Antarctic region. Reindeer, polar bears, Arctic foxes, and other creatures can be found in the northern hemisphere's polar region.
• People in diverse parts of the world adjust to natural conditions based on the seasonal cycle.
• When the food supply becomes scarce due to extreme cold weather, a lot of birds and animals migrate temporarily.
• Trees grow fruit during a specific season. As a result, agricultural seasons are also affected by local climate conditions/seasons.