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Earth and Space - Earth's Rotation and Revolution (Day/Night and Seasons)

Grade 4IB

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

🔑Concepts

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Earth's Rotation: The Earth spins on its imaginary line called an axis. One full rotation takes approximately 2424 hours, which creates the cycle of day and night.

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The Axis: Earth's axis is not straight; it is tilted at an angle of 23.5∘23.5^\circ. This tilt is crucial for the changing of seasons.

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Earth's Revolution: While rotating, the Earth also travels in an elliptical orbit around the Sun. This movement is called revolution and takes approximately 36514365 \frac{1}{4} days (one year).

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Causes of Seasons: Seasons occur because of the fixed 23.5∘23.5^\circ tilt of the Earth's axis and its revolution around the Sun. Different parts of the Earth receive more or less direct sunlight at different times of the year.

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Hemispheres: When the Northern Hemisphere is tilted toward the Sun, it experiences Summer due to more direct sunlight and longer days. At the same time, the Southern Hemisphere is tilted away and experiences Winter.

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Solstices and Equinoxes: These are specific points in Earth's orbit marking the start of seasons. During an Equinox, day and night are approximately equal in length (1212 hours each).

📐Formulae

1 Rotation≈24 hours1 \text{ Rotation} \approx 24 \text{ hours}

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

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

💡Examples

Problem 1:

If the Earth stopped rotating but continued to revolve around the Sun, would we still have day and night cycles? Explain using time units.

Solution:

Yes, but a single 'day' would last one full year (36514365 \frac{1}{4} days).

Explanation:

Without rotation, a specific side of the Earth would face the Sun for half of its orbit (approx. 182.5182.5 days) and face away for the other half. The 2424 hour day/night cycle depends entirely on rotation.

Problem 2:

Why is it colder in the Winter even though the Sun is still in the sky?

Solution:

Due to the 23.5∘23.5^\circ tilt, the Sun's rays hit the Earth at a shallow angle.

Explanation:

When a hemisphere is tilted away from the Sun, the solar energy is spread over a larger area, and the days are shorter, resulting in less heat absorption compared to the direct rays of Summer.

Problem 3:

Calculate how many hours are in one full Earth revolution (assume 1 year=3651 \text{ year} = 365 days).

Solution:

365×24=8,760 hours365 \times 24 = 8,760 \text{ hours}

Explanation:

To find the total hours in a year, we multiply the number of days in a revolution (365365) by the number of hours in one rotation (2424).