The moon is one of the most important of the heavenly bodies. Her tide-raising force is of great importance to mankind. Her silvery light is always welcoming at night.
Origin of the moon
It is generally accepted by the astronomers that the moon and the earth were formerly one body which had probably been thrown off from the central body of the solar system. The appearance of the moon was caused by the attraction of the sun on the earth when it entered a danger zone during the course of her irregular movements.
The entire mass had, at the time, a high temperature and was in a fluid condition, and rotated rapidly about an axis. Gradually, it cooled and contracted with a corresponding increase in its rate of rotation. It is also held, although not so convincingly, that moon and the earth were originally separate bodies.
Surface structure of the moon
The important features on the surface of the moon were revealed by a small telescope. But for minor details better instruments are necessary. Our naked eye sees the figure of “man in the moon”. The giant telescopes show that it is a series of high mountains and craters, much like the rugged physical features of our own planet.
With the magnification of telescope, the moon is in effect brought to a distance of about 240 miles from the earth. Thus, we can see quite clearly the objects on her surface. On only one side of the moon, which can be seen, there are lofty mountain ranges, cracks, rills, craters, etc. the most numerous object to be seen on the moon are the so-called craters, mountainous ring formations which are to be found all over the visible surface.
The rills are narrow, deep valleys, usually not straight, they differ from the cracks and clefts which are perfectly straight and may run for hundreds of miles through mountains and valleys. The craters are said to have a volcanic origin.
Physical conditions on the moon
It has no atmosphere encircling its globe. It is known with certainty that it is a dead world. It is also certain that there is no water on the moon. There is little or no appearance of erosion or weathering on the lunar mountains or craters and there are no clouds to be seen at any time.
Although competent observers have occasionally seen patches of a greenish hue which have been thought to show signs of change during the course of the lunar month and have been contractually interpreted as vegetation, the existence of any vegetation is very improbable because there is no atmosphere or water for the existence of any vegetation.
The second Russian lunar probe, which succeeded in hitting the moon, contained a magnetometer to observe any lunar magnetism. This operated to within 50 miles of the surface, but recorded no magnetic field, suggesting that the moon can not have any appreciable magnetism. Supporting evidence is provided by the failure to observe any zones of intense particle radiation around the moon due to trapping by a lunar magnetic field.
The third Russian lunar probe passed behind the moon and took photograph of that part of the lunar surface which is never visible from the earth. These photographs were automatically processed and scanned for transmission by radio signal, on command from the earth, and the next point of closest approach of the vehicle to the earth. From these data the picture was reconstructed on the earth, showing for the first time some of the hidden features of the moon.
The most striking feature of the moon is its changing phases, its waxing and waning or the variation of its visible outline. It waxes from the position of new moon through crescent shape to new moon, after a full lunar month. The explanation of these phases is very simple. The moon has no inherent brightness of its own.
But owing to the high reflecting power of its surface, it is able to reflect back some of the light from the sun which falls upon it. It is by means of the light reflected from that portion of the surface which is illuminated by the sun that the moon becomes visible to us.
As it journeys round the earth, presenting the same phase to us at all times, we see different amounts of her illuminated surface on different days. The moon like other members of the solar system possesses two movements of rotation and revolution. The phase that we always observe her on the same surface, establishes that the periods of rotation and revolution are equal i.e. on the lunar surface a month is of one day.
At the seaside, it is noticed that the level stretch of sand or rock at the foot of the cliffs is now covered by the sea and now left bare. It tide comes in and goes out twice every day. Every month there is a great tide which occurs on the night of full moon. It is mainly due to the attraction excreted by the moon on the waters of the ocean that the tides are caused.
As the attraction of the moon on the water (fluid) is greater than its attraction on the earth (solid), water is heaped up at the point directly under the moon. The water level on the other side of the globe falls down at the same time. The sun has also an attraction on both the water and the land. But being far away it has no appreciable effect
It is the tides which reduce great rocks to fragments and keep the ocean water moving. They are also of enormous economic importance to mankind. Water can be stored in upraised tanks and allowed to run down in hydro-electric plants and turn the wheels of huge generators.
When earth comes directly between the sun and the moon, it becomes invisible, because the shadow of the earth falls on it, and the light of the sun is not allowed to fall on the it. A partial lunar eclipse occurs when shadow of the earth falls partially on it.
The eclipse does not happen every month, because the orbit of the moon is inclined at the angle of about 5 degrees to the ecliptic. Lunar eclipse takes place only at the time of full moon.
Eclipse of the sun and the moon are possible only when the sun is near one of the nodes of the moons orbit. In an interval of 6,585 days and 8 hours, i.e. 18 years 10 or 11 days, the sun and the moon return to approximately the same position with respect to one of the nodes of the moon’s surface.
The period is called the “saros”. The total number of eclipses in one saros is about 70, of which 41 are usually solar and 29 solar. Of the solar eclipses 14 are partial, 17 annular and 10 totals. Working on the saros basis, one can predict number of eclipses.
The age of the moon
It is held that the moon has not always been where it is now. In the distant past it was very close. George Darwin (son of the biologist Charles Darwin) established that the moon is constantly receding from the earth at the rate of about five inches every year.
In view of the fact that tidal waves running around and around our globe encounter resistance in the form of continents that stand in their way, and the body of the earth rotates between two break shoes, we as the axle of the wheel rotates between two brake shoes, we should expect that the rotation of the earth would be slowed down gradually. This would cause a gradual increase in the length of our day.
According to a fundamental law of mechanics, known as the law of conversion of angular momentum, this lengthening of the day must result in the lengthening of the rotation period of the moon (month) and in a gradual increase in it distance from the earth.
Dividing the present distance to the moon (239,000 miles) by the estimate rate of recession (5 inches per year) we find that the moon must have been practically in contact with the earth about four billion years ago. One surprising result of these calculations is that, at that time, the length of a month (moon’s orbital period) was equal to the length of a day ( earth’s diurnal period), both being equal to 7 present day hours.
Facts about the moon
The following are the facts about the moon:
- Distance from the earth
- Greatest-252,710 miles
- Mean 238,857
- Volume-1/81 that of the earth
- Mass-1/81 that of the earth
- Density-3/5 that of the earth
- Velocity of escape-i.5 map’s
- Temperature Noon-250F
- Temperature at night-215F
- Period of revolution around the earth 37 days, 7 hours.
- Period of axial rotation 43 minutes and 11.5 seconds
- Average velocity of moon around the earth is 2,287 M.P.H. or 3.350 feet per second.
- (In one hour the moon moves a distance about equal to its own diameter). Full moon gives about 1/465,000 as lighter as the sun.
- The geology of the moon is called Selenography.
- Over 3,000 craters are visible these include:
- Walled plains Diameter 60,150 miles; floor not much lower than outside.
- Rugged plains Diameter 10-60 miles: uniform and circular; floor usually much lower than outside.
- True craters Diameter 18 miles to less than 1 mile; deep and cone shaped; deepest is Newton’s crater with rim 23,800 feet above interior.
- Highest mountain is about five miles above average surface level.
- Rays Bright streaks 5- 10 miles wide and up to 1500 miles long. Rills Narrow crevices 10-300 miles long and less than 2 miles wide.
- Seas 14 recognized large, smooth, dark areas. Cover about half of visible area, predominate in the north.