Lesson Notes By Weeks and Term v5 - Grade 7

Lesson Video

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Performance objectives

• Describe the movements of the Earth, Moon, and Sun.
• Explain how Earth's movements cause day, night, and seasons.
• Identify the different phases of the Moon.
• Explain what causes solar and lunar eclipses.
• Relate tides to the Moon's gravitational pull.

Lesson summary

This week, we'll be diving into the fascinating relationships between the Earth, the Moon, and the Sun. Understanding these relationships isn't just about learning science; it helps us understand why we have day and night, why we experience seasons, and how the Moon influences our tides. In South Africa, many cultural practices and traditional farming methods are linked to the lunar cycle and seasonal changes. Knowing about these relationships helps us appreciate our cultural heritage and make informed decisions about our lives. For example, knowing about the phases of the moon can help coastal communities predict high and low tides, important for fishing and coastal management.

Lesson notes

2.1 The Earth's Rotation and Revolution: Rotation: The Earth spins on its axis, an imaginary line running from the North Pole to the South Pole. This spinning motion is called rotation. One complete rotation takes approximately 24 hours, which is what we call a day. As South Africa rotates into the sunlight, we experience sunrise, and as it rotates away, we experience sunset.

Revolution: The Earth also travels around the Sun in a path called its orbit. This movement is called revolution. One complete revolution takes approximately 365.25 days, which is what we call a year. The Earth's orbit is not a perfect circle; it's slightly elliptical (oval-shaped). 2.2 The Earth's Tilt and Seasons: The Earth's axis is tilted at an angle of approximately 23.5 degrees. This tilt is crucial for the seasons. As the Earth revolves around the Sun, different parts of the Earth are tilted towards or away from the Sun at different times of the year. Summer in South Africa (December - February): The Southern Hemisphere (where South Africa is located) is tilted towards the Sun. This means we receive more direct sunlight and longer days, resulting in warmer temperatures.

Winter in South Africa (June - August): The Southern Hemisphere is tilted away from the Sun. We receive less direct sunlight and shorter days, leading to cooler temperatures. Autumn (March - May) and Spring (September - November): These are transition periods when neither hemisphere is tilted significantly towards or away from the Sun, resulting in more moderate temperatures.

Example: Imagine holding a globe and shining a torch (representing the Sun) on it. Tilt the globe so the Southern Hemisphere is closer to the torch. The Southern Hemisphere receives more direct light, representing summer. Now tilt it the other way; the Northern Hemisphere receives more light, while the Southern Hemisphere experiences winter. 2.3 The Moon's Phases: The Moon orbits the Earth. The different shapes we see the Moon in the sky are called phases. These phases are caused by the changing angles at which we see the Moon's illuminated surface as it orbits the Earth.

New Moon: The Moon is between the Earth and the Sun. We cannot see the Moon because the side facing us is not illuminated.

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

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. "Waning" means getting smaller.

Third Quarter: Half of the Moon is illuminated again, but the opposite half compared to the First Quarter.

Waning Crescent: A small sliver of the Moon remains visible before it disappears again at the New Moon. It takes approximately 29.5 days for the Moon to go through all its phases. This is called a lunar cycle.

Example: Observe the Moon over several weeks. Keep a Moon diary and draw the shape of the Moon each night. You will notice how the Moon's appearance changes, going through the different phases. 2.4 Eclipses: Eclipses occur when the Sun, Earth, and Moon align in a straight line.

Solar Eclipse: A solar eclipse happens when the Moon passes between the Sun and the Earth, blocking the Sun's light. In South Africa, a total solar eclipse is a rare and spectacular event. Only a small area of the Earth experiences a total solar eclipse; the rest experience a partial solar eclipse. Important Safety

Note: Never look directly at the Sun during a solar eclipse without proper eye protection (eclipse glasses).

Lunar Eclipse: A lunar eclipse happens when the Earth passes between the Sun and the Moon, casting a shadow on the Moon. During a lunar eclipse, the Moon may appear reddish in colour because some sunlight is bent (refracted) through the Earth's atmosphere. Lunar eclipses are safer to view with the naked eye than solar eclipses. 2.5 Tides: Tides are the rise and fall of sea levels caused by the gravitational pull of the Moon and, to a lesser extent, the Sun.

High Tide: When the Moon's gravity pulls on the Earth, it causes the water to bulge out on the side of the Earth facing the Moon and on the opposite side. These bulges are high tides.

Low Tide: Areas between the bulges experience low tides.

Spring Tides: When the Sun, Earth, and Moon are aligned (during the New Moon and Full Moon phases), their gravitational forces combine, resulting in higher high tides and lower low tides.

Neap Tides: When the Sun, Earth, and Moon are at right angles to each other (during the First Quarter and Third Quarter phases), the Sun's gravity partially cancels out the Moon's gravity, resulting in less extreme high and low tides.

Example: Imagine the Earth covered in a thin layer of water. The Moon's gravity pulls the water towards it, creating a bulge. As the Earth rotates, different locations pass through this bulge, experiencing high tide.