Lesson Notes By Weeks and Term v5 - Grade 7

Lesson Video

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Performance objectives

• Describe the relative positions and movements of the Earth, Moon, and Sun.
• Explain the phases of the Moon.
• Explain the causes of solar and lunar eclipses.
• Describe how the Earth's rotation causes day and night.
• Relate the lunar cycle to cultural practices and calendars.

Lesson summary

The relationship between the Earth, Moon, and Sun is fundamental to understanding our place in the universe and influences many aspects of our daily lives. From the changing seasons that affect agriculture in the Free State to the tides that impact coastal fishing communities in KwaZulu-Natal, these celestial bodies play a crucial role. Understanding their movements and interactions helps us predict and adapt to natural phenomena, understand the calendar we use every day and even interpret cultural practices linked to lunar cycles. This week, we will explore these connections in detail.

Lesson notes

2. 1.

Earth's Rotation and Revolution: Rotation: The Earth spins on its axis, an imaginary line passing through the North and South Poles. One complete rotation takes approximately 24 hours, which we experience as a day and night. Because South Africa is located in the Southern Hemisphere, when it is facing the Sun, we experience daytime. As the Earth rotates, different parts of the world face the Sun, creating the cycle of day and night. This rotation is what allows us to have sunrise and sunset every day.

Example: Imagine holding a ball (representing Earth) and shining a torch (representing the Sun) on it. As you slowly turn the ball, notice how different parts are lit by the torch, simulating day, while other parts are in darkness, simulating night.

Revolution: The Earth orbits (revolves) around the Sun in an elliptical (oval-shaped) path. One complete revolution takes approximately 365.25 days, which we call a year. The Earth's axis is tilted at an angle of about 23.5 degrees relative to its orbital plane. This tilt is responsible for the seasons. During the year, the angle at which sunlight strikes South Africa varies, leading to warmer summers when the Southern Hemisphere is tilted towards the Sun and cooler winters when it's tilted away.

Example: During summer (December, January, February) in South Africa, the sun is higher in the sky, leading to longer days and more direct sunlight, hence warmer temperatures. Conversely, during winter (June, July, August) the sun is lower in the sky, days are shorter, and the sunlight is less direct, resulting in cooler temperatures. 2.

2. The Moon's Orbit and Phases: Orbit: The Moon orbits the Earth in an elliptical path. One complete orbit takes approximately 27.3 days. This is called the sidereal month.

Phases of the Moon: The Moon does not produce its own light. We see it because it reflects sunlight. As the Moon orbits the Earth, we see different amounts of the illuminated surface, resulting in the phases of the Moon. The cycle of lunar phases (from new moon to new moon) takes approximately 29.5 days (a synodic month).

New Moon: The Moon is between the Earth and the Sun. The side of the Moon facing us is not illuminated, so we cannot see it.

Waxing Crescent: A small sliver of the Moon becomes visible as it moves away from the Sun.

First Quarter: Half of the Moon is illuminated.

Waxing Gibbous: More than half of the Moon is illuminated.

Full Moon: The entire face of the Moon is illuminated.

Waning Gibbous: The illuminated portion of the Moon starts to decrease.

Third Quarter: Half of the Moon is illuminated, but the opposite half from the First Quarter.

Waning Crescent: A small sliver of the Moon remains visible before it disappears again at the New Moon.

Mnemonics to Remember the Phases: A helpful way to remember is "Waxing (gaining light) on the right, waning (losing light) on the right".

Tidal Locking: The Moon is tidally locked with Earth, meaning that the Moon rotates once on its axis in the same time it takes to orbit the Earth. This means we always see the same side of the Moon from Earth. 2.

3. Eclipses: Solar Eclipse: A solar eclipse occurs when the Moon passes between the Sun and the Earth, blocking the Sun's light. This can only happen during a new moon. Solar eclipses are relatively rare because the Moon's orbit is tilted relative to the Earth's orbit around the Sun.

Types of Solar Eclipses: Total Solar Eclipse: The Moon completely covers the Sun. This is visible only from a narrow path on Earth.

Partial Solar Eclipse: The Moon only partially covers the Sun.

Annular Solar Eclipse: The Moon appears smaller than the Sun, leaving a bright ring (annulus) around the Moon.

Lunar Eclipse: A lunar eclipse occurs when the Earth passes between the Sun and the Moon, casting a shadow on the Moon. This can only happen during a full moon. Lunar eclipses are more common than solar eclipses and are visible from a wider area of Earth.

Types of Lunar Eclipses: Total Lunar Eclipse: The Moon passes completely into the Earth's umbra (the darkest part of the shadow), causing the Moon to appear reddish in color (often called a "blood moon").

Partial Lunar Eclipse: Only part of the Moon passes into the Earth's umbra.

Penumbral Lunar Eclipse: The Moon passes through the Earth's penumbra (the lighter part of the shadow). This is often difficult to notice. 2.4 Calendar Systems: Many cultures have developed their calendar systems based on the movements of the sun and moon.

Examples: Solar Calendar: Based on the Earth’s revolution around the Sun (e.g., Gregorian calendar).

Lunar Calendar: Based on the Moon's orbit around the Earth (e.g., Islamic calendar).

Lunisolar Calendar: Combines both solar and lunar cycles (e.g., some traditional African calendars, Chinese calendar). Guided Practice (With Solutions)

Question 1: Explain why we experience day and night on Earth.

Solution: The Earth rotates on its axis, completing one rotation approximately every 24 hours.