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Earth and Space - The movement of the Earth and other planets relative to the Sun

Grade 5Cambridge (IGCSE)

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

🔑Concepts

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The Sun is at the center of our solar system, and all planets, including Earth, move around it. This is known as the heliocentricheliocentric model.

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The Earth rotates on its axis, which is an imaginary line running through the North and South Poles. One full rotation takes approximately 2424 hours, which creates day and night.

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The Earth revolves around the Sun in a path called an orbit. One complete revolution takes 36514365 \frac{1}{4} days, which we define as one year.

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The planets are held in their orbits by the force of gravity from the Sun.

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The distance from the Sun affects the time it takes for a planet to complete one orbit. Planets closer to the Sun, like Mercury, have shorter years than planets further away, like Neptune.

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Earth and the other planets are approximately spherical in shape (geoidgeoid for Earth) due to gravity pulling matter toward the center.

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The Moon is a natural satellite that orbits the Earth, taking approximately 27.327.3 days to complete one revolution.

📐Formulae

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

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

T∝r3T \propto \sqrt{r^3} (Kepler's Third Law relationship: The orbital period TT increases as the distance rr from the Sun increases)

💡Examples

Problem 1:

If the Earth takes 365.25365.25 days to orbit the Sun, why do we usually say a year has 365365 days, and what happens to the extra 0.250.25 day?

Solution:

We add a 'Leap Day' (29th29^{th} February) every 44 years.

Explanation:

Because 0.25×4=10.25 \times 4 = 1 full day, we add one extra day every four years to keep our calendar aligned with the Earth's actual position in its orbit around the Sun.

Problem 2:

Planet A is 58 million km58 \text{ million km} from the Sun, while Planet B is 150 million km150 \text{ million km} from the Sun. Which planet has a longer 'year'?

Solution:

Planet B.

Explanation:

According to the principles of planetary motion, the further a planet is from the Sun, the larger its orbital path and the slower its orbital speed, resulting in a longer period of revolution (TT).

Problem 3:

Explain why we experience day and night on Earth using the concept of rotation.

Solution:

As the Earth rotates 360∘360^{\circ} on its axis, only one half faces the Sun at a time.

Explanation:

The half facing the Sun experiences day, while the half facing away experiences night. One full cycle of this rotation takes 2424 hours.