WAXING AND WANING MOON

The moon appears to grow and decay. What really happens? It is just an interplay of light and shadow.

Like earth, half of the moon's surface is illuminated by sun light always. The moon circles the earth every 28 days. when it shows fully illuminated face, we say it is full moon day. When it shows night side(dark side), it is new moon day. If it shows partly night side and day side, it must be either in waxing or waning phase. The figure illustrate the concept beautifully.

When we see exactly half moon, the earth, the sun and the moon must form a right angled triangle as shown in the diagram. The angle suspended at the earth is 89.85 degrees.
The trigonometry says :

COS(89.85) = distance between the moon and the earth / distance between sun and the earth = .002617
Reversing both sides,
distance between sun and the earth / distance between the moon and the earth = 1/0.002617 = 382

Hence sun's distance is 382 times the moon's distance from the earth. The moon is roughly at 400000 km from the earth. So the sun is at 382 x 400000 km from the earth. The trigonometry always plays the important role in astronomical calculations.

Moon's cycle is used as measurement of time till date (a month). Moon's phases gave us romance; threatened us; made us quiet and artist. There are many beliefs that surrounds the moon's phases.

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