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

Grade 5IGCSE

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.

The movement of the Earth and other planets relative to the Sun Revision - Grade 5 Science IGCSE