MadSci Network: Other

Re: Full Moon and Not enough Dirt

Date: Fri Aug 19 17:29:15 2005
Posted By: John Christie, Faculty, Dept. of Chemistry,
Area of science: Other
ID: 1124399629.Ot

Is it true that if you dig a hole in the ground when there is a full moon, there won't be enough dirt to fill it back up? If so, can you explain why? Thank you.

Hi Ashley.

I am fairly sure that it is not true (but I cannot guarantee it 100%). If it is true, then I cannot explain why, and I doubt that you would find another scientist who could.

In science, when you are looking for a cause and an effect, there has to be some plausible connection. The suggestion that the moon could have a significant effect on the dirt you have dug out of a hole is a bit like suggesting that Fred in Miami gets red ears every time Bill in Seattle sneezes!

Perhaps the best thing would be to try it out -- dig a hole, putting all the dirt on a canvas sheet to make sure you do not lose any, and then fill it in. You neeed to do it at least twice. Once, the moon should be full, the other time it should be near new. Everything else should be matched as closely as possible. Similar soil, similar weather conditions, same time of day, same size of hole. But do not re-dig the same hole, because the state of soil compaction is an important factor.

What I think you will find is that both times you will have some soil left over, because when you put the soil back in the hole it will not be as efficiently nor tightly packed. I think there will be roughly, but not exactly the same amount left over each time.

What plausible effect could the moon have on the soil? Well, the moon's gravity has an effect roughly three millionths of that of the earth's gravity at the earth's surface. That means that 1 kilogram of soil would weigh 0.999 997 kg wt when the moon is overhead, and 1.000003 kg wt when the moon is on the other side of the earth. However, these conditions are not the same as full moon and new moon. If the full moon is overhead, then it must be the middle of the night, and so the sun's gravity is pulling in the opposite direction to the moon's, and the soil would weigh more about half of a millionth of a kilogram weight more, say about 0.999975 kg wt. But none of these things are nearly as large as the difference between the earth's gravity at the equator and at the poles, which makes a difference of a few parts per thousand, or about a thousand times as much!

Apart from gravity, there is no other influence described by current scientific knowledge. Perhaps there is some (alleged) astrological influence of the moon on the soil, but that is not part of science.

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