Earth, Moon and the Sun — NCERT Class 7: 18 flashcards
All 18 flashcards from this kit, free and with no sign-up.
1. What is the Sun?
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The Sun is a medium-sized star at the centre of our solar system and the main source of light and heat for Earth.
2. Why does the Moon shine?
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The Moon is non-luminous; it shines by reflecting sunlight.
3. How long does the Moon take to revolve around Earth?
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About 29–30 days (roughly one month).
4. What causes the phases of the Moon?
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The changing amount of the sunlit half of the Moon that is visible from Earth as the Moon revolves around Earth.
5. What is a New Moon?
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The phase when the lit half of the Moon faces away from Earth, so we see no lit part.
6. What is a Full Moon?
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The phase when the entire visible disc of the Moon is lit.
7. What is the lunar month?
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The cycle from New Moon to Full Moon and back to New Moon, about 29–30 days.
8. When does a solar eclipse occur?
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When the Moon comes between the Sun and Earth and blocks sunlight, on a New Moon day.
9. When does a lunar eclipse occur?
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When Earth comes between the Sun and the Moon and Earth's shadow falls on the Moon, on a Full Moon day.
10. Why don't eclipses happen every month?
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Because the Moon's orbit is tilted relative to Earth's orbit around the Sun, so the three bodies rarely line up perfectly.
11. What causes day and night?
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Earth rotates on its axis once every 24 hours; the side facing the Sun has day and the side away has night.
12. What causes seasons?
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Earth's tilted axis combined with its revolution around the Sun, so different parts receive more direct sunlight at different times of the year.
13. What causes tides?
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The Moon's gravitational pull on Earth's oceans, along with the Sun's pull.
14. What are spring tides?
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Stronger tides that occur at New Moon and Full Moon when the Sun and Moon pull in the same direction.
15. What are neap tides?
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Weaker tides that occur at quarter phases when the Sun and Moon pull at right angles.
16. Why does the Moon look bigger at the horizon?
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It is an optical illusion; the Moon's actual angular size does not change.
17. What is the difference between luminous and non-luminous bodies?
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Luminous bodies give out their own light (like the Sun); non-luminous bodies only reflect light (like the Moon and Earth).
18. How long does Earth take to revolve around the Sun?
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About one year.
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