krit.club logo

Earth and Space - Explaining day and night through Earth's rotation

Grade 5IGCSE

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

🔑Concepts

•

The Earth is a sphere that rotates on an imaginary line called an axis, which runs from the North Pole to the South Pole.

•

The Earth's axis is not perfectly vertical; it is tilted at an angle of approximately 23.5∘23.5^\circ.

•

One full rotation of the Earth takes approximately 2424 hours, which we define as one day.

•

The Earth rotates from West to East (counter-clockwise when viewed from above the North Pole).

•

Daylight is caused by a location on Earth facing the Sun and receiving light energy. Night occurs when that same location rotates away from the Sun into the Earth's own shadow.

•

The Sun appears to move across the sky from East to West because of the Earth's rotation in the opposite direction (West to East). This is known as apparent motion.

•

Shadows change in length and position throughout the day. They are longest in the early morning and late afternoon and shortest at 'solar noon' when the Sun is at its highest point.

📐Formulae

1 full rotation=24 hours1 \text{ full rotation} = 24 \text{ hours}

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

Speed of rotation at the Equator≈1,670 km/h\text{Speed of rotation at the Equator} \approx 1,670 \text{ km/h}

💡Examples

Problem 1:

If the Earth takes 2424 hours to complete a full 360∘360^\circ rotation, how many degrees does it rotate in 11 hour?

Solution:

15∘15^\circ per hour.

Explanation:

To find the degrees per hour, we divide the total degrees in a circle by the total hours in a day: 360∘24 hours=15∘/hour\frac{360^\circ}{24 \text{ hours}} = 15^\circ/\text{hour}.

Problem 2:

A student in London (UK) is experiencing midday (12:0012:00 PM). What is likely happening on the exact opposite side of the Earth in New Zealand?

Solution:

It is likely midnight (12:0012:00 AM).

Explanation:

Because the Earth is a sphere, when one side faces the Sun (Day), the opposite side is facing away from the Sun (Night). Since the Earth has rotated 180∘180^\circ relative to the Sun between these two points, the time difference is 242=12\frac{24}{2} = 12 hours.

Problem 3:

Explain why the Sun rises in the East every morning.

Solution:

Because the Earth rotates toward the East.

Explanation:

The Earth spins from West to East. As your location on Earth turns toward the East, the Sun first becomes visible over the Eastern horizon, creating the illusion that the Sun is moving.