Phases of the Moon

By: Samuel Martin

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What is the Lunar Cycle?

The lunar cycle the path of the sunlit portion of the Moon as seen by a person on Earth. The lunar phases change as the Moon orbits the Earth, moving with the positions of the Sun relative to the Earth.

In the lunar cycle, there are 8 distinct phases, which includes New Moon, Waxing Crescent, 1st Quarter, Waxing Gibbous, Full Moon, Waning Gibbous, 3rd Quarter, Waning Crescent, and then it repeats. The moon takes 27.3 to orbit Earth, but from New Moon to New Moon, it takes 29.5 days.

What are the 1st and 3rd quarter?

The 1st and 3rd Quarter are phases of the moon, in which you can only see (from Earth) half of the moon.

When a quarter is Waxing, the light we can see is getting bigger, as in the 1st Quarter. When a phase is Waning, the sunlit area is getting smaller, like shown in the 3rd Quarter.

Differences Between 1st and 3rd Quarters

The 3 main differences between these two phases of the moon include, but are not limited to:

  • Time of Day: The 1st quarter always happens in the night/evening sky, while the 3rd quarter takes place in the morning. At first quarter, the moon in its month-long orbit has just passed the sun, where lots of people see it, but since the last quarter rises around midnight, fewer people see it.

  • Sunlight in the Moon: At first quarter, the illuminated area of the moon is growing (waxing). Every night the moon's sunlit area gets larger, becoming a gibbous, until a week later the moon is at the full phase. At last quarter it is getting smaller (waning), until the moon has shrunk to nothing (New Moon).

  • Features of the Moon: At first quarter, we see the western part of the moon's face (when viewed from earth). Landmarks like the Sea of Serenity & Sea of Tranquility are shown. The last quarter shows the eastern half (still as viewed from earth), with features such as the Sea of Rains and the Sea of Clouds.

SImilarities Between 1st and 3rd Quarters

Some of the similarities between these phases of the moon include:

  • Sunlight in the Moon: When the moon is in these phases, you can only see 50% of the moon (from Earth).

  • Location Around the Earth: When looking at a diagram of the moon phases, these two phases are located directly at 90 Degrees from the New and Full Moon Phases.


My perspective on Earth is different from that of an astronaut in space, because I can only see the part of the moon that is lit by the reflected sunlight, but when an astronaut looks at the moon, they can see the whole moon, even the backside, that most of us will never see. Another thing that only astronauts will see is how the moon will always be halfway lit. At any phase in the cycle we can see the 'phase', but they only see half of the moon being lit.