Lesson Notes By Weeks and Term v5 - Grade 7

Lesson Video

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Performance objectives

• Explain the causes of day and night.
• Describe the phases of the Moon and their sequence.
• Explain how the Earth's tilt causes seasons in the Southern Hemisphere.
• Define solar and lunar eclipses.
• Model the Earth-Moon-Sun system.

Lesson summary

The relationships between the Earth, Moon, and Sun are fundamental to understanding our planet and our place in the solar system. This topic explains why we have day and night, different seasons, and the phases of the Moon. Understanding these cycles allows us to predict events like eclipses and helps us appreciate the dynamic nature of the world around us. For South African learners, this knowledge is crucial for understanding cultural traditions related to lunar cycles and agricultural practices linked to the seasons.

Furthermore, a solid foundation in this area of Natural Sciences is essential for future studies in Geography, Astronomy, and other related fields.

Lesson notes

2.1 Day and Night The Earth rotates on its axis, an imaginary line passing through the North and South Poles. This rotation takes approximately 24 hours, which we call a day. As the Earth rotates, different parts of its surface face the Sun. The side facing the Sun experiences daylight, while the side facing away from the Sun experiences night. Why? The Earth is a sphere. Only one side can face the Sun at a time. How? Imagine holding a ball (representing the Earth) and shining a torch (representing the Sun) on it. As you slowly turn the ball, you'll see that different parts of the ball are lit up, while other parts are in shadow. This is exactly what happens on Earth. 2.2 The Lunar Phases The Moon orbits the Earth approximately every 29.5 days. The Moon does not produce its own light. We see the Moon because it reflects sunlight. As the Moon orbits the Earth, we see different amounts of the illuminated portion of the Moon, resulting in the lunar phases.

The main phases are: 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. "Waxing" means growing.

First Quarter: Half of the Moon is illuminated.

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

Full Moon: The entire Moon is illuminated.

Waning Gibbous: More than half of the Moon is illuminated, but the illuminated portion is decreasing. "Waning" means shrinking.

Third Quarter: Half of the Moon is illuminated (the opposite half from the First Quarter).

Waning Crescent: A small sliver of the Moon is visible again, decreasing until the New Moon. Why? The Moon is orbiting around the Earth, changing its angle relative to the Sun and Earth. How? Imagine holding a small ball (representing the Moon) and walking around a larger ball (representing the Earth) while holding a torch (representing the Sun) in a fixed position. As you walk around, you'll see different amounts of the small ball illuminated. 2.3 The Seasons The Earth's axis is tilted at an angle of 23.5 degrees. This tilt, combined with the Earth's orbit around the Sun, causes the seasons. During the year, different parts of the Earth are tilted towards the Sun. When the Southern Hemisphere is tilted towards the Sun, it experiences summer, and the Northern Hemisphere experiences winter. When the Southern Hemisphere is tilted away from the Sun, it experiences winter, and the Northern Hemisphere experiences summer.

Summer (December - February): The Southern Hemisphere is tilted towards the Sun. Days are longer, and temperatures are warmer.

Autumn (March - May): The Southern Hemisphere is tilting away from the Sun. Days are getting shorter, and temperatures are cooling down.

Winter (June - August): The Southern Hemisphere is tilted away from the Sun. Days are shorter, and temperatures are colder.

Spring (September - November): The Southern Hemisphere is tilting towards the Sun. Days are getting longer, and temperatures are warming up. Why? The Earth is tilted, so different parts of the world get more direct sunlight at different times of the year. How? Imagine holding a globe with a tilted axis and moving it around a light bulb. Notice how the amount of light shining on the Southern Hemisphere changes as you move the globe around. 2.4 Eclipses An eclipse occurs when one celestial body blocks the light from another celestial body.

There are two main types of eclipses: Solar Eclipse: A solar eclipse occurs when the Moon passes between the Sun and the Earth, blocking the Sun's light. From a certain location on Earth, the Sun appears to be partially or completely covered by the Moon. This can only happen during a New Moon. It is extremely dangerous to look directly at the Sun during a solar eclipse.* Lunar Eclipse: A lunar eclipse occurs when the Earth passes between the Sun and the Moon, casting a shadow on the Moon. The Moon appears dimmer or reddish. This can only happen during a Full Moon. Why? Sometimes the Earth, Moon, and Sun line up perfectly. How? Use three objects to represent the Earth, Moon, and Sun and demonstrate the positions during a solar and lunar eclipse. Emphasize the importance of never looking directly at the sun during a solar eclipse.

Example: It is July in Durban. What season is it, and why?

Answer: It is winter in Durban. This is because the Southern Hemisphere (where Durban is located) is tilted away from the Sun during this time of year. This means that Durban receives less direct sunlight, resulting in colder temperatures and shorter days. Guided Practice (With Solutions)

Question 1: Why do we have day and night on Earth?

Solution: We have day and night because the Earth rotates on its axis. As the Earth rotates, different parts of the surface face the Sun (day) and face away from the Sun (night).

Question 2: What phase of the Moon would you expect to see if you observed the Moon exactly one week after a New Moon? Explain your reasoning.