Astrology: moon phases and how to tell the time from the moon
Astrology The Moon - Phases and Telling Time
.Ken Ward's Astrology Pages
|While we have only mentioned one way of telling the time at
night using the stars, there are many ways of doing this. You can, however, tell the time
at night in areas where the sun isn't visible by observing the moon. The table below shows
drawings of the moon from the new moon to the waxing crescent. This page contains:
When the moon is gradually showing more and more of its illuminated surface, we say that it is waxing, which also means "to grow in size, strength and power". When the moon is gradually showing less and less of its illuminated surface, we say it is waning, which also means "to decrease in size, strength and power."
The moon is gibbous when it is more than half illuminated and less than full. The word gibbous means "humpbacked".
The moon repeats its cycle approximately every 29½ days. This figure is slightly less than the average number of days in a month, so occasionally there are two full moons in a month. This occurs approximately every 2.7 years. When this second occurrence of the moon in a month occurs, it is called a blue moon. It therefore follows that "once in a blue moon" means once every 2.7 years :-)
Each season normally has 3 full moons. Occasionally, there are four. For religious purposes, it is the third moon in a four moon season that is considered the odd one out. For more information see Sky and Telescope.
You can tell the time from the moon, because the phases of the moon are the result of the relative position of the sun and the moon. This means that the position of the sun below the horizon can be determined by the phase of the moon. When the moon is new, the sun is behind the moon, and the moon sets and rises approximately at the same time as the sun. When the moon is full, the sun is opposite the moon, and the moon rises when the sun sets (approximately). In these case, the sun is 180 degrees opposite the position of the moon. In other cases, where the moon is a crescent, quarter or gibbous, the sun's position can be determined from the moon's position. And by knowing the sun's position, we can determine the time. The moon, therefore acts as an indicator of the sun's position. The following diagram shows this in greater detail. Half of the moon is always illuminated by the sun (barring eclipses, etc). So the moon phases appear to us as crescents, gibbous, etc, because of the angle between the moon and the sun.
The diagram above, which isn't to size or scale, of course, considers the sun to be stationary and the moon to move. When the moon is in line with the sun and between it and the earth, then there is a new moon. When the sun and the moon are in line with the earth in between, then there is a full noon. Between this are the other phases. When is the moon is at 90º to the sun, then it will be a half-moon (a quarter of the moon is visible to us). The crescent and the gibbous are at 45º and 135º respectively.
Because the moon isn't always visible at night (unlike the stars, which almost always are visible, weather permitting), the moon is less useful as a means of telling time. For example, when there is a new moon, the moon and the sun set at almost the same time, so the moon no more available than the sun.