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5.5Chapter 5: The Earth in Space

The Moon — Alhussan Physics - Stage 7 Revision Notes & Topical Questions

5 min read 7 parts Lesson 5 of 11 1 quiz

📚 Alhussan Physics - Stage 7 Hub / Topical Revision
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Lesson summary

5.5 The Moon — Lunar Phases, Solar Eclipses and Lunar Eclipses — Alhussan International Academy — Physics (Stages 7–9) notes: Explain why we see phases of the Moon, solar and lunar eclipses, and tides.Seen day and night — you can see the Moon in the sky during the day and during …

  • Reflected light
  • Orbit time
  • Cycle length
  • Not the Earth's shadow
  • Expectation
  • Tilted orbit

Part 1 of 5Moonlight

Seen day and night
  • Seen day and night you can see the Moon in the sky during the day and during the night.
Reflected light
  • Reflected light the Moon does not give out light itself, and moonlight is reflected sunlight.
Lit half
  • Lit half the light from the Sun lights up half of the Moon, just as it lights up half of every planet and moon in the Solar System.

Part 2 of 5Phases of the Moon

1Orbit time
  • Orbit time the Moon orbits the Earth every 27.3 days.
2Phases
Phases the regular changes in the Moon's shape seen from Earth.
  • The Moon appears to change shape because it moves around the Earth, so we see different amounts of its lit half.
3Order
  • Order new Moon, waxing crescent, first quarter, waxing gibbous, full Moon, waning gibbous, last (third) quarter and waning crescent.
  • At new Moon we see none of the lit half, and at full Moon we see the whole lit half.
4Cycle length
  • Cycle length the cycle of phases takes about 29.5 days, because the Earth also moves round the Sun.
5Same face
  • Same face the Moon always shows the same face to the Earth because it spins once in each orbit.
6Not the Earth's shadow
  • Not the Earth's shadow phases come from viewing the lit half from different angles.

Part 3 of 5Eclipses

Shadow
  • Shadow when an object moves in front of a source of light, a shadow is formed, which can happen when the Moon or the Earth moves in front of the Sun.
Solar eclipse
Solar eclipse when the Moon passes between the Sun and the Earth and blocks the light from the Sun.
  • The region of deep shadow, or umbra, is where you see a total eclipse.
  • Outside that region, in the penumbra, you see a partial eclipse.
  • Total eclipses are seen because the Moon happens to be the right size and distance from the Earth to exactly cover the Sun, which is a coincidence.
Lunar eclipse
Lunar eclipse when the Earth comes between the Sun and the Moon, so the Moon is in the shadow of the Earth.

Part 4 of 5Why eclipses are rare

Why eclipses are rare
Expectation
  • Expectation you might expect an eclipse every 27.3 days, because the Moon orbits the Earth in that time.
Tilted orbit
  • Tilted orbit the orbit of the Moon is tilted slightly, and the Earth, Sun and Moon need to be lined up for an eclipse to happen.
If the orbit was not tilted
  • If the orbit was not tilted the Earth would block out the light every month and we would never see a full moon.

Part 5 of 5Tides

Cause
  • Cause water in the oceans is free to move, and the gravitational attraction of the Moon and Sun produces tides.
Bulges
  • Bulges there is a bulge of water on either side of the Earth due to the force of gravity from the Moon.
  • The Earth spins through the bulges, producing two high tides a day.
Spring tides
  • Spring tides when the Sun and Moon are aligned, their pulls add up, giving a higher tide with very high high tides and very low low tides.
  • They happen at new Moon and full Moon.
Neap tides
  • Neap tides when the Sun and Moon are not aligned, such as at right angles at the quarter Moons, the pulls partly cancel, giving a lower tidal range.
EventAlignment
Solar eclipseSun, Moon, Earth
Lunar eclipseSun, Earth, Moon
Spring tideSun and Moon in line with Earth
  • Connection
    • a new Moon, a solar eclipse and a spring tide all happen when the Sun, Moon and Earth are in line.

Key terms

TermMeaning
Phases of the Moonthe changing shape of the lit part of the Moon seen over a month.
Solar eclipsewhen the Moon passes between the Sun and Earth, blocking sunlight.
Lunar eclipsewhen the Earth passes between the Sun and the Moon, so the Moon is in Earth's shadow.
Spring tidea higher tide when the Sun and Moon are aligned.
Natural satellitean object that orbits a planet, such as the Moon.
Umbrathe region of deep shadow where a total eclipse is seen.

Avoid these mistakes

1
Thinking the Moon makes its own light — it reflects sunlight.
2
Thinking phases are caused by the Earth's shadow — they come from seeing the lit half from different angles.
3
Thinking eclipses happen every month — the tilt of the Moon's orbit stops this.
4
Mixing up solar and lunar eclipses — in a solar eclipse the Moon is between the Sun and Earth, and in a lunar eclipse the Earth is between the Sun and Moon.

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