Phases of the Moon
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flagWhat you'll discover
- arrow_forwardExplain why the Moon seems to change shape
- arrow_forwardName the eight Moon phases in order
- arrow_forwardBust the myth that phases are Earth’s shadow
- arrow_forwardConnect purnima and aunsi to Full Moon and New Moon
Half the Moon is always lit
The Moon makes no light of its own — it only reflects sunlight. At every moment, the half of the Moon facing the Sun is bright and the other half is dark, exactly like Earth’s day and night sides.
What changes during the month is not the lighting, but our viewpoint. As the Moon travels around Earth, we see different amounts of its lit half. That changing view is what we call the phases.
Not Earth’s shadow!
Many people think the Moon’s phases are caused by Earth’s shadow falling on it. That is a myth! Earth’s shadow only touches the Moon during a lunar eclipse, which is rare.
Prove it in the simulation: drag the Moon to the first-quarter position. Earth is not between the Sun and Moon at all, yet we still see only half a bright Moon. The dark part is simply the Moon’s own night side turned toward us.
The eight phases
Starting from New Moon (the Moon sits between us and the Sun, its dark side faces us), the lit part grows — waxing. We see Waxing Crescent, First Quarter, Waxing Gibbous and then Full Moon, when Earth is between... no wait, when the Moon’s lit side fully faces us.
Then the light shrinks — waning: Waning Gibbous, Last Quarter, Waning Crescent and back to New Moon. The whole cycle takes about 29.5 days, which is why "month" and "Moon" are related words.
The Moon in the Nepali calendar
Nepali life follows the Moon closely. Purnima is the Full Moon and aunsi is the New Moon, and the lunar fortnights between them set the dates of festivals: Buddha Jayanti on Baisakh Purnima, Janai Purnima, and Laxmi Puja near Kartik aunsi.
So when you drag the Moon to the "Full" position in this simulation, you are looking at a purnima night — the same Moon that lights up festival nights across Nepal every month.