New moon — Science definition

The phase when the Moon's unlit side faces Earth, making it nearly invisible in the sky; the start (and end) of the monthly cycle.

Where it is taught

In use

When the Moon sits roughly between Earth and the Sun, its lit half faces away from us and we see almost nothing — a new moon.

Earth, Moon & Sun: Moon Phases

Questions using new moon

Problem 1

Which phase comes right after a new moon?
  1. Waxing crescent
  2. Full moon
  3. Waning gibbous
  4. Third quarter
Answer and explanation

Waxing crescent

Right after new moon, a thin sliver of light begins to grow — that's the waxing crescent.

Problem 2

About how many days does one full cycle of moon phases take, from new moon back to new moon?
Answer and explanation

29.5 days

One synodic month is about 29.5 days.

Problem 3

A student argues that first quarter must show one quarter of the lunar disk lit and every new Moon causes a solar eclipse. Correct both statements with geometry.
Answer and explanation

First quarter describes about one-quarter of the phase cycle and the visible disk is roughly half lit. New Moon alone does not guarantee a solar eclipse because the tilted lunar orbit usually misses the shadow line; alignment near a node is also needed.

First quarter describes about one-quarter of the phase cycle and the visible disk is roughly half lit. New Moon alone does not guarantee a solar eclipse because the tilted lunar orbit usually misses the shadow line; alignment near a node is also needed.

Response criteria

  • Use the stated measurements or conditions, with correct units.
  • Connect the result to the physical mechanism or evidence relationship.
  • Identify the assumption, model limit or further evidence requested.

Problem 4

Independent chapter check: A student argues that first quarter must show one quarter of the lunar disk lit and every new Moon causes a solar eclipse. Correct both statements with geometry.
Answer and explanation

First quarter describes about one-quarter of the phase cycle and the visible disk is roughly half lit. New Moon alone does not guarantee a solar eclipse because the tilted lunar orbit usually misses the shadow line; alignment near a node is also needed.

First quarter describes about one-quarter of the phase cycle and the visible disk is roughly half lit. New Moon alone does not guarantee a solar eclipse because the tilted lunar orbit usually misses the shadow line; alignment near a node is also needed.

Response criteria

  • Use the stated measurements or conditions, with correct units.
  • Connect the result to the physical mechanism or evidence relationship.
  • Identify the assumption, model limit or further evidence requested.

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