Question

What is crescent moon?

Answer 1

Hy
Here is your answer
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A crescent shape is a symbol or emblem used to represent the lunar phase in the first quarter, or by extension a symbol representing the Moon itself. It is used as the astrological symbol for the Moon, and hence as the alchemical symbol for silver.

Answer 2

HEY!!

A crescent moon is one of the phases of the Moon. Like it's name, it looks like a crescent. 

In one lunar phase [See related Link - Crescent Moon] you will see two crescents. One just after the Moon comes out of the Earths shadow (New Moon), and one just before the Moon disappears into the Earths shadow. See related Link - Phases of the Moon for a pictorial representation.