Forest Preserve District of Cook County, Illinois
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The Moon
Nature Bulletin No. 253-A   January 21, 1967
Forest Preserve District of Cook County
Richard B. Ogilvie, President
Roland F. Eisenbeis, Supt. of Conservation

On January 22 there will be a full moon and, unless it is cloudy, this "circled orb" will rise in the eastern sky, a little after sunset, like a broad round golden mirror. That' s what it really is: a sort of mirror that reflects the light of the sun back to us. People used to plan their work, journeys and festivities according to the sign of the moon so that they could use its light. In every kitchen there was an almanac which showed the days of the week and month, the times of sunrise, sunset, moonrise and moonset, the signs of the moon, the eclipses, and the signs of the zodiac. Certain crops were planted only "in the light of the moon"-- others, like potatoes and turnips, only "in the dark of the moon". Some superstitious folks would not have their hair cut, butcher meat, trim vines or shingle a house except when the moon was "right".

After "full moon", it rises later and later each evening -- an average of about 51 minutes later each day -- until, at the end of a week, it doesn't rise until about midnight. Then, partly turned away from the sun, half shaded and half bright, it is said to be in its "last quarter". Another week later, the moon is "dark", rising a little before sunrise with only a feebly-shining slender crescent along the one edge. A day or two later, it is seen in the west just after sunset and is said to be a "new moon". A week later it is overhead at sunset, is half lighted, and is in the "first quarter". The time between one new moon and the next averages 29-1/2 days, varying somewhat according to the season and the latitude.

The moon's path around the earth is an ellipse, so that its distance from us varies -- averaging about 240,000 miles. The sun is over 90 million miles away. Occasionally, as the moon moves directly in front of the sun, its shadow sweeps across a rather narrow strip somewhere on the earth's surface, producing an eclipse of the sun. Within that shadow it becomes so dark that chickens go to roost and we turn the street lights on. Likewise, the earth's shadow occasionally falls on the face of a full moon to produce an eclipse but, because the earth's diameter is four times greater, that eclipse is sometimes visible all over the world.

The moon ' s path around the earth is not quite in line with the plane of the earth's path around the sun. Because of this tilt, the "full" and "dark" moons are usually above or below the line between the earth and the sun. Otherwise, every new moon would eclipse the sun and every full moon would be eclipsed by the earth. The plane of the moon' s orbit swings back and forth, which explains why in some years it ranges farther north and farther south in the sky than in other years. These and other irregularities combine to make it a most difficult task to chart and predict the phases and eclipses of our celestial playmate.

Recently, pictures have been taken of the moon and there are plans to visit the satellite in the near future. It has no air, no clouds, no water. The sun shines for about 15 days, followed by 15 days of darkness. During the long moon day, the starts would shine in an inky black sky and the barren surface would be hotter than boiling water. At night the temperature would plunge to about 460F. degrees below zero. A 200-lb. athlete would weigh only 33 pounds and could easily jump over a house.

No one has ever seen the other side of the moon. On our side it has very steep mountain ranges rising over 30,000 feet, and is pocked with thousands of circular craters, some of which are 100 miles across. The broad dark patches that the ancients thought were seas, and which suggest the "man in the moon" to imaginative people, are flat deserts covered with lava or volcanic ash.

It is responsible for our tides and most June weddings.

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