6.1.1 The Earth (3)
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1.
Describe how the Earth's orbit around the Sun causes variations in the length of daylight hours throughout the year. Explain how these variations contribute to the seasonal changes.
The Earth's orbit around the Sun is not perfectly circular; it's slightly elliptical. While the distance between the Earth and the Sun varies throughout the year, this variation is relatively small compared to the effect of the axial tilt. The more significant factor is the tilt itself.
Because of the 23.5-degree tilt, the angle at which sunlight strikes the Earth's surface changes throughout the year. During summer in the Northern Hemisphere, the Northern Hemisphere is tilted towards the Sun. This means the sunlight strikes the Northern Hemisphere at a steeper angle, concentrating the solar energy and resulting in longer daylight hours. Conversely, during winter in the Northern Hemisphere, the sunlight strikes at a shallower angle, spreading the solar energy over a larger area and resulting in shorter daylight hours.
The opposite occurs in the Southern Hemisphere. When the Northern Hemisphere is experiencing summer, the Southern Hemisphere is experiencing winter, and vice versa. The variations in daylight hours directly influence the amount of solar radiation received, which in turn determines the temperature and thus the season.
2.
A satellite is orbiting the Earth in a circular orbit. The average radius of the orbit is 4000 km and the orbital period is 90 minutes. Calculate the average orbital speed of the satellite. Use the equation v = 2πr / T, where v is the average orbital speed, r is the average radius of the orbit, and T is the orbital period.
Solution:
Given:
- r = 4000 km = 4.0 x 106 m
- T = 90 minutes = 90 x 60 seconds = 5400 seconds
Formula: v = 2πr / T
Calculation:
v = (2 x π x 4.0 x 106 m) / 5400 s
v ≈ 586 m/s
Answer: The average orbital speed of the satellite is approximately 586 m/s.
3.
A student states: "The Moon's phases are caused by the Earth blocking sunlight from reaching different parts of the Moon." Explain why this statement is incorrect and describe the actual cause of the Moon's phases.
The student's statement is incorrect. The Moon's phases are not caused by the Earth blocking sunlight. Instead, the phases are caused by the changing angles at which we view the sunlit portion of the Moon as it orbits the Earth.
The Moon itself does not produce its own light; it reflects sunlight. As the Moon orbits the Earth, different amounts of its sunlit surface become visible to us. The amount of the sunlit portion we see changes because the relative positions of the Earth, Moon, and Sun are constantly changing. When the Moon is between the Earth and the Sun, the sunlit side faces away from us (New Moon). As it moves in its orbit, we see more and more of the sunlit side, resulting in phases like Crescent, Quarter, Gibbous, and finally Full Moon. The phases are a result of geometry – the changing angles of illumination as viewed from Earth, not the Earth blocking sunlight.