Measurement of Time Monthly Events

Strictly speaking in order of time, the first class of uniformities from which the measurement of time proceeded were in all probability the lunar phenomena, from which we got the grouping of days into months and weeks (quarter months).

There are still backward peoples who have not learned to reckon in years of equivalent length. The recognition of the month is wellnigh universal even among hunting tribes with no settled agriculture. Moonlight is a circumstance of enormous importance in the everyday life of people who have crude means of artificial illumination. Even today in remote parts of the country the time of full moon is chosen for a long night journey.

An interval of roughly thirty days separates one full moon or new moon from another. The two half moons, the first "quarter" when waxing and the third "quarter" when waning, complete the division of the month into quarters, which roughly correspond to our week. Near the sea it is noticed that the tides are exceptionally), high when the moon is invisible through the whole night (new moon) and when it is full. At first and third quarter (half moons) the high-water mark is exceptionally low. The most important thing connected with the changing appearance of the moon is that as the moon waxes and wanes it rises towards the east a little later every day. At first quarter it is already high in the heavens at sunset, setting about midnight. The full moon rises about sunset, is at its highest about midnight, and sets towards sunrise. At the third quarter the waning moon does not rise till about midnight, is seen at its highest point ("crosses the meridian") about sunrise, and is visible during the morning by daylight.

The moon seems to partake of the general motion of the celestial sphere, rising in the east and setting in the west. If it rises at the same time as a particular star cluster on a particular night in the month, the same constellation will rise a little earlier than the moon on the night following. A week later it would already be above the pole at moonrise. Thus the moon itself seems to be slipping backwards in the opposite direction to the apparent rotation of the sun and fixed stars, so that it gets back to where it was before after a definite interval of days and nights, i.e. what we call roughly a month. Alternatively we may say that it rotates round the earth in about a month in the same direction as the earth's axial or diurnal motion. Whichever way we look at it, the moon has a motion of its own, independent of the apparent motion of the fixed stars.

No comments: