Expert: Steven LJ Russo - 5/2/2007

Question
Hi!
Can you clarify my doubt below. i will be grateful to you if you could devote your time and effor for this.

I would like to know how a full moon and new moon occurs. Let's take Asia and Americas as example. If it is new moon in Asia, it is the same in Americas.
If moon wanes because of earth shadow, it wanes from right to left and it again waxes from left to right. how this is possible. if earth's shadow hides moon then the moon should wax from right to left and not from left to right.

Is this because of rotation of moon and earth. can you please explain this?


Regards
T.S.Sudharsan  

Answer
A Full Moon is when you have the Sun, Moon, and Earth in a "straight line, and from the Earth, we see the Moon fully lit by sunlight.

When we have a new moon, the Moon is in between the Earth and the Sun, so the lit up side of the Moon faces away from us.

The Moon Waxes from New Moon to Full Moon and the "right side is lit up".  It Wanes from Full to New, and the left side is lit up.

It is NOT the Earths shadow that causes the phases, but how much of the Moon is lit up as seen from the Earth.

See this link:

http://www.astro.wisc.edu/~dolan/java/MoonPhase.html

Steve