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Earth and Space - Causes of Day, Night, and Seasons

Grade 6IGCSE

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

🔑Concepts

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The Earth rotates on its imaginary axis from West to East. This rotation takes approximately 2424 hours to complete, which results in the cycle of day and night.

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The Earth's axis is not vertical; it is tilted at an angle of approximately 23.5∘23.5^\circ from the perpendicular to its orbital plane.

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Day and night occur because only half of the Earth faces the Sun at any given time. The side facing the Sun experiences day, while the side facing away experiences night.

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The Earth revolves around the Sun in an elliptical orbit. One full revolution takes approximately 365.25365.25 days, which we define as one year.

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Seasons are caused by the 23.5∘23.5^\circ tilt of the Earth's axis as it orbits the Sun. This tilt causes different parts of the Earth to receive varying intensities and durations of sunlight throughout the year.

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When a hemisphere is tilted towards the Sun, it experiences Summer (longer days and more direct sunlight). When it is tilted away, it experiences Winter (shorter days and indirect sunlight).

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Solstices are the two times a year when the Sun reaches its highest or lowest point in the sky at noon, marked by the longest and shortest days. Equinoxes are times when day and night are of approximately equal length (around 1212 hours each).

📐Formulae

1 Solar Day=24 hours1\text{ Solar Day} = 24\text{ hours}

1 Year≈365.25 days1\text{ Year} \approx 365.25\text{ days}

Earth’s Axial Tilt≈23.5∘\text{Earth's Axial Tilt} \approx 23.5^\circ

Angular Speed of Rotation=360∘24 h=15∘/hour\text{Angular Speed of Rotation} = \frac{360^\circ}{24\text{ h}} = 15^\circ/\text{hour}

💡Examples

Problem 1:

Explain why the Sun appears to rise in the East and set in the West.

Solution:

This is due to the Earth's rotation on its axis from West to East.

Explanation:

As the Earth spins counter-clockwise (when viewed from above the North Pole), stationary objects in space like the Sun appear to move in the opposite direction (East to West) across our sky.

Problem 2:

If the Earth's axis were at an angle of 0∘0^\circ (no tilt), how would this affect the seasons?

Solution:

There would be no seasons; every location on Earth would experience the same weather patterns and roughly 1212 hours of daylight year-round.

Explanation:

Seasons depend on the changing angle of sunlight hitting the Earth. With a 0∘0^\circ tilt, the Sun's rays would always hit the Equator directly and the poles indirectly, without any change as the Earth orbits the Sun.

Problem 3:

Calculate how many degrees the Earth rotates in 44 hours.

Solution:

60∘60^\circ

Explanation:

Since the Earth completes a full 360∘360^\circ rotation in 2424 hours, the rate of rotation is 360∘24 h=15∘/h\frac{360^\circ}{24\text{ h}} = 15^\circ/\text{h}. For 44 hours: 15∘/h×4 h=60∘15^\circ/\text{h} \times 4\text{ h} = 60^\circ.

Causes of Day, Night, and Seasons - Revision Notes & Key Formulas | IGCSE Grade 6 Science