Keeping Time with the Skies
The phases of the Moon
Record the Moon's shape over a month and find the pattern in its phases.
Look over your records and a clear pattern appears.
From a full circle, the bright part shrinks to a half circle in about a week, then keeps shrinking for another week until you can't see the Moon at all. This two weeks of shrinking is the waning period, called Krishna Paksha in India. (Waning rhymes with yawning: the Moon is getting sleepy and going to sleep.)
| Day | Name |
|---|---|
| the Moon is a full bright circle | full Moon, Purnima |
| the Moon can't be seen at all | new Moon, Amavasya |
After the new Moon the bright part grows back: to a half circle in about a week, and to a full Moon in another week. This growing period is the waxing period, called Shukla Paksha. (Think: the Moon is fixing itself back to full.)
The shapes in between have names too:
| Phase | What you see |
|---|---|
| gibbous | more than half of the lit part, puffed out like a balloon |
| crescent | less than half, a thin C-shape |
Waning, then waxing, over and over: from one full Moon to the next takes about a month.
These changing shapes of the Moon's bright part, from day to day as seen from the Earth, are called the phases of the Moon. The Moon itself never changes size; only the bright part we see changes.
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