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Earth and Space - Causes of Seasons

Grade 6IB

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

🔑Concepts

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Earth's Axis: The Earth is tilted on its axis at an angle of approximately 23.5∘23.5^\circ relative to its orbital plane.

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Revolution: The Earth revolves around the Sun in an elliptical orbit, completing one full revolution in approximately 365.25365.25 days.

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Angle of Insolation: The intensity of solar energy depends on the angle at which sunlight hits the surface. Direct rays (90∘90^\circ) concentrate energy over a smaller area, leading to higher temperatures.

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Hemispheric Seasons: Because of the fixed axial tilt, when the Northern Hemisphere is tilted towards the Sun, it receives more direct sunlight (Summer), while the Southern Hemisphere is tilted away (Winter).

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Solstices: Occur twice a year when the tilt of Earth's axis is most inclined toward or away from the Sun. The Summer Solstice occurs at approximately 23.5∘N23.5^\circ N (Tropic of Cancer) or 23.5∘S23.5^\circ S (Tropic of Capricorn).

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Equinoxes: Occur when the Sun is directly above the Equator (0∘0^\circ latitude), resulting in nearly equal day and night across the globe.

📐Formulae

Axial Tilt≈23.5∘\text{Axial Tilt} \approx 23.5^\circ

Orbital Period(T)≈365.25 days\text{Orbital Period} (T) \approx 365.25 \text{ days}

I∝sin⁡(θ) (where I is light intensity and θ is the angle of incidence)I \propto \sin(\theta) \text{ (where } I \text{ is light intensity and } \theta \text{ is the angle of incidence)}

💡Examples

Problem 1:

Explain why the Northern Hemisphere experiences Summer in June even though Earth is slightly further from the Sun (Aphelion) during this time.

Solution:

Summer is caused by the tilt of the Earth, not the distance from the Sun.

Explanation:

In June, the Northern Hemisphere is tilted toward the Sun at an angle of 23.5∘23.5^\circ. This causes the Sun's rays to hit the surface more directly (closer to 90∘90^\circ), leading to a higher concentration of energy per unit area and longer daylight hours.

Problem 2:

If the Earth's axial tilt were 0∘0^\circ instead of 23.5∘23.5^\circ, how would the seasons change?

Solution:

There would be no seasonal changes.

Explanation:

Without a tilt, the angle of insolation at any given latitude would remain constant throughout the year-long revolution. Every location would experience approximately 1212 hours of daylight and 1212 hours of darkness every day.

Problem 3:

Calculate the difference in daylight hours at the Equator during an Equinox.

Solution:

12 hours of daylight≈12 hours of darkness12 \text{ hours of daylight} \approx 12 \text{ hours of darkness}

Explanation:

During an Equinox, the Sun's rays are perpendicular to the Earth's axis at the Equator (0∘0^\circ). The circle of illumination passes through both poles, bisecting all latitudes evenly.