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Why does the Moon keep changing its shape ?

The alignment of the Moon and the Sun determines the phase of the Moon.

The waxing crescent moon grows till it is about half full in the phase we call first quarter. From there it grows to full moon and then begins to shrink back to third quarter, waning crescent and finally back to new moon.

pahase of the moonNorthern Hemisphere
Phases of the moon as seen in the Northern Hemisphere

Northern Hemisphere
Phases of the moon as seen in the Southern Hemisphere

The images below show the different phases of the moon in one Lunar month for the Northern Hemisphere


 Waning crescent

Last quarter
(Half Moon)

  Waning gibbous

Day 25
Day 21
Day 17

    The Moon is 90 degrees west of the sun  
The Sun

New Moon
Day 0


The angular distance of the sun and moon is small, less than a few degrees.

Full Moon
Day 14

The moon is 180 degrees from the sun.

The Earth




Day 3

Day 7

Day 10

Waxing crescent

First quarter
or Half Moon

Waxing gibbous
    The Moon is 90 degrees east of the Sun  

When the bright part is getting bigger, the Moon is waxing.

When it is getting smaller, the Moon is waning.

When the Moon is more than half-lit, it is called a gibbous Moon.

When the moon is less than half-lit, it is called a crescent Moon.

Times for the main phasesnext page
previous pageIntroduction to the different moon phases
icon moon Introduction to phases icon moon Tips for Moon watching
icon moon Shapes of the Moon icon moon Moon around the world
icon moon Time to see each phase icon moon Facts about the Moon
icon moon Moon Calendar icon moon Moon animation
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I teach computers at The Granville School and St. John's Primary School in Sevenoaks Kent.