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Earth, Moon, and the Sun - Seasons on the Earth

Grade 7CBSE

Review the key concepts, formulae, and examples before starting your quiz.

🔑Concepts

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The Earth has two types of motions: Rotation (spinning on its axis) and Revolution (movement around the Sun). Rotation causes day and night, while Revolution, combined with the tilted axis, causes seasons.

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The Earth's axis is tilted at an angle of 23.5∘23.5^{\circ} (or 2312∘23\frac{1}{2}^{\circ}) to the vertical line perpendicular to its orbital plane. This means the axis makes an angle of 66.5∘66.5^{\circ} (or 6612∘66\frac{1}{2}^{\circ}) with the orbital plane itself.

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The Earth takes approximately 36514365\frac{1}{4} days to complete one revolution around the Sun. We consider a year as 365365 days, and the remaining 14\frac{1}{4} day (66 hours) is added every four years to form a Leap Year of 366366 days.

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Summer Solstice occurs on June 21st when the Northern Hemisphere is tilted towards the Sun. The Sun's rays fall directly on the Tropic of Cancer (23.5∘N23.5^{\circ} N), resulting in the longest day and shortest night in the Northern Hemisphere.

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Winter Solstice occurs on December 22nd when the Southern Hemisphere is tilted towards the Sun. The Sun's rays fall directly on the Tropic of Capricorn (23.5∘S23.5^{\circ} S), causing summer in the Southern Hemisphere and winter in the Northern Hemisphere.

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Equinoxes occur on March 21st (Vernal/Spring Equinox) and September 23rd (Autumnal Equinox). During these days, the Sun shines directly over the Equator (0∘0^{\circ}), and the entire Earth experiences equal lengths of day and night.

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Seasons change because of the change in the position of the Earth around the Sun and the fixed tilt of its axis. When a hemisphere is tilted towards the Sun, it receives more direct sunlight and has longer days, leading to Summer. When tilted away, it receives slanting rays and has shorter days, leading to Winter.

📐Formulae

Angle with Orbital Plane=90∘−Tilt Angle\text{Angle with Orbital Plane} = 90^{\circ} - \text{Tilt Angle}

Tilt Angle=23.5∘\text{Tilt Angle} = 23.5^{\circ}

Angle with Orbital Plane=90∘−23.5∘=66.5∘\text{Angle with Orbital Plane} = 90^{\circ} - 23.5^{\circ} = 66.5^{\circ}

Leap Year Duration=365 days+(4×6 hours)=366 days\text{Leap Year Duration} = 365 \text{ days} + (4 \times 6 \text{ hours}) = 366 \text{ days}

💡Examples

Problem 1:

If the Earth's axis were not tilted and was instead perpendicular to the orbital plane, what would be the effect on the seasons?

Solution:

There would be no change in seasons throughout the year.

Explanation:

The primary cause of seasons is the 23.5∘23.5^{\circ} tilt. If the tilt were 0∘0^{\circ}, every point on Earth would receive the same amount of solar radiation and daylight hours (12 hours each) throughout the year, resulting in a constant climate for any given latitude.

Problem 2:

Why does the Northern Hemisphere experience Summer while the Southern Hemisphere experiences Winter in the month of June?

Solution:

Due to the tilt of the Earth, the Northern Hemisphere is inclined towards the Sun in June.

Explanation:

On June 21st (Summer Solstice), the Sun's rays fall vertically on the Tropic of Cancer (23.5∘N23.5^{\circ} N). Since the Northern Hemisphere is tilted towards the Sun, it receives more heat and light (longer days), while the Southern Hemisphere is tilted away, receiving slanting rays and less heat (shorter days).

Problem 3:

Calculate the total number of hours gained over 4 years that leads to the creation of a Leap Year.

Solution:

24 hours24 \text{ hours}

Explanation:

The Earth takes 365365 days and 66 hours to revolve around the Sun. In 4 years, the extra time accumulated is: 4 years×6 hours/year=24 hours4 \text{ years} \times 6 \text{ hours/year} = 24 \text{ hours} Since 24 hours=1 day24 \text{ hours} = 1 \text{ day}, this extra day is added to the month of February every fourth year.