Earth, Moon & Sun: Moon Phases — Drills · Grade 9 Science

Chapter: Earth, Moon & Solar System

What these drills covers

By the end of Earth, Moon & Sun: Moon Phases you should be able to:

8 questions, multiple choice, numeric and written answer, each with a worked explanation.

Vocabulary used: phase, waxing, waning, new moon, synodic month.

Problem 1

Moon phases are caused by
  1. Earth's shadow on the Moon
  2. the changing angle from which we see the Moon's sunlit half
  3. clouds
  4. the Moon's own light
Answer and explanation

the changing angle from which we see the Moon's sunlit half

Half the Moon is always lit; the phase is how much of that half faces Earth.

Problem 2

How many days, approximately, does one complete cycle of Moon phases take?
Answer and explanation

29.5 days

About 29.5 days from new moon to new moon.

Problem 3

At new moon, the Moon is
  1. between Earth and the Sun
  2. behind Earth from the Sun
  3. at right angles
  4. in Earth's shadow
Answer and explanation

between Earth and the Sun

Its sunlit side faces away from Earth, so it appears dark.

Problem 4

A solar eclipse can only happen at
  1. full moon
  2. new moon
  3. first quarter
  4. any phase
Answer and explanation

new moon

The Moon must be between Earth and the Sun to block it.

Problem 5

Eclipses do not occur every month because
  1. the Moon's orbit is tilted relative to Earth's orbit
  2. the Moon disappears
  3. Earth stops rotating
  4. the Sun moves
Answer and explanation

the Moon's orbit is tilted relative to Earth's orbit

The roughly 5° tilt means the three bodies usually fail to line up exactly.

Problem 6

We always see the same face of the Moon because
  1. the Moon does not rotate
  2. its rotation period equals its orbital period
  3. Earth does not rotate
  4. of its phases
Answer and explanation

its rotation period equals its orbital period

Tidal locking makes one rotation take exactly one orbit.

Problem 7

Explain why a lunar eclipse is visible to far more people than a solar eclipse.
Answer and explanation

In a lunar eclipse Earth's shadow falls on the Moon, so anyone on the night side of Earth who can see the Moon sees it darken — roughly half the planet at once. In a solar eclipse the Moon's much smaller shadow falls on Earth, and totality is confined to a narrow track a few hundred kilometres wide, so only people within that track see it.

Response criteria

  • State a scientifically accurate conclusion.
  • Show the data, mechanism, or calculation that supports it.
  • Include units, conditions, or limits where relevant.

Problem 8

A student says the Moon's phases are caused by Earth's shadow. Correct this and give the evidence.
Answer and explanation

Phases come from the changing angle at which we view the Moon's permanently sunlit half, not from Earth's shadow. The evidence is that a full moon occurs when the Moon is opposite the Sun — exactly where Earth's shadow would fall — yet it is fully lit rather than dark, and phases cycle smoothly every month while eclipses are rare. Earth's shadow does cause lunar eclipses, which is a separate and occasional event.

Response criteria

  • State a scientifically accurate conclusion.
  • Show the data, mechanism, or calculation that supports it.
  • Include units, conditions, or limits where relevant.

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