THE IMPORTANCE OF THE MOON
The moon has been important to man ever since he recognised it appeared and moved in a regular cycle just as the Sun appears to do. The moon has been used as the basis for many calendar systems. On our site we have incorporated a Moon Phase predictor to tell anyone who is interested, the current phase of the moon, it's age (in days since the last New Moon) how far through the current lunar cycle we are (as a percentage) whether it is Waxing or Waning, (and also if it is Crescent or Gibbous - see below) as well as the date of the next New Moon and Full Moon events.
This article is intended to provide a very brief explanation of why things appear as they do - of course, you don't need to understand any of the mechanics to use the information. Our Moon Phase predicition is very accurate (within a minute or so of the actual events).
We've also provided a table of accurate times for the the New Moon, 1st Quarter, Full Moon and Last Quarter events for the current year so you can plan ahead if you need to.
SOME COMMON FACTS
As most people are probably aware by now, the earth is not flat, it's a sphere (or at least very nearly). It is continuously orbited by a satallite which we call the Moon and both the Moon and the Earth are are illuminated by the Sun (from some 93 million miles away).
For about half of every day the moon is actually in the field of vision of an observer at any point on the earth (you can't always see it of course - particularly during the hours of daylight).
The amount of the moon which is visible at any point in time is the same for any observer on earth. This can be anything from from no moon illuminated at all (New moon or dark of the moon), to the full disc illuminated (Full Moon). The orientation does appear to change for any observer and is different at all latitudes - this is explained a little later.
Because the motion of the Moon and Earth are cyclical, it is possible to predict mathematically how much of the moon will be visible at any time in the future (or the past). We've done all the hard sums for you and so the picture shown on our moonphase gadget is more or less what would see if it was visible to you.
WAXING AND WANING
In the northern hemisphere the from a New moon (when nothing is visible) the first crescent appears from the right and grows bigger each day until it reaches the full disc position (Full Moon) during this period, the Moon is said to be Waxing. After the full moon, the disk starts to shrink again, this time towards the left, until the final crescent disappears off the left hand side ready for the next New Moon. During this latter period, the Moon is said to be Waning. In the southern hemisphere, exactly the opposite happens (ie the crescent appears to grow from left to right).
This Waxing - Full - Waning cycle gives rise to the Triple Goddess symbol )O( seen so much in wiccan circles.
The moon is said to be Gibbous when its phase lies between the 1st and last quarter (ie. when more than half of the moon disc is visible).
HOW LONG EACH CYCLE TAKES
As observed from the Earth, the Moon takes around 29.5 days to go from Full Moon to Full Moon (this is known as the Synodic month if you are interested). So that's how long it takes the Moon to orbit the Earth, Right? - Well no actually; If the Earth and Sun were in fixed positions in space, we would observe that the Moon actually takes about 27.32 days to orbit the Earth (this is known as the sidereal month).
So why the difference? Well planetary motion is a complex thing and the truth is, while the Moon is orbiting the Earth at a fixed rate, the Earth itself is orbiting the Sun and so the light source which illuminates the moon is apparently changing its position (The earth moves about a degree along its path around the sun every day). This has the affect of extending the period we observe for the lunar cycle.
It all sounds very complex and the mathematics of prediction is horrendous. Luckily you don't need to understand any of that to use our site but perhaps we should admire the incredible brains of the scentists who figured it all out over the centuries. And just imagine the feelings of the engineers at NASA who sent spacecraft to the moon - this involves firing the capsule towards some point in outer space and hoping that about 4 days later, the moon gets there at the same time. If they had got the sums wrong, the Apollo astronauts would have had an endless journey to the edge of our Universe. Luckily, the moon did arrive when it was supposed to and the rest is history.