Many people ask that question, because that is how they believe the moon influences the markets.
There's often some nice trends at the time of the full moon, but it's not for the reason that you would assume.
Perry Kaufmann is a financial market mathematician, so it's all very statistically based, and in his book 'Trading Systems & Methods' this is what he says:
"It is known that the moon's effect on our planet is great - it is vitally connected with the movement of all fluids. Because of its large presence and close proximity to the Earth, the moon is also believed to affect human behaviour in strange ways, especially during a new or full moon.
"In an experiment conducted on an arbitrary set of futures markets for the year 1972, it was shown that short-term movements of prices react with some uniformity with respect to the phases of the moon. In fact, the markets chosen for observation - silver, wheat, cattle,cocoa and sugar - showed an uncanny ability to form a rising market following a full moon and a falling market after a new moon."
However, that's not the way any confirmed lunatic uses the moon to trade - there are a few on these boards. However, just put up an intraday chart for the date of a full moon, and days either side of it, and see for yourself.