The time when the full moon occurs (usually but not always around the 14th or 15th of the month) has always fascinated people. In order to fully understand what actually happens, some background information is needed.
How and Why it Happens
The only time this celestial phenomenon can happen is when the moon is on the other side of the planet. That is, it is opposite the sun. In astronomical terms, this would be when the degree difference of the sun and moon is 180 degrees longitude.
The Lunar Month
The lunar month refers to the period between two new moons. There are many different types of lunar months, and different calculations are used. Some determine it using the moon’s orbital period. Others use the space between the new moons. Most however, are between 27 to 29 days. For this reason, when the full moon occurs it’s usually every 29 days or so.
The various lunar months can make for some different calculations. Some of them include the following.
The Sidereal Month
The calculation is derived from the time the moon passes a star upon the sky. The time is 27 days and 7 hours.
The Synodic Month
This period is between two new moons. A new moon takes place when its ecliptic longitude is nearly equal to the sun. At 29 days and 12 hours, it is longer than the sidereal month.
The Anomalistic Month and Others
There is also the anomalistic month. The measurement is derived from its orbit when it’s nearest the planet. It is 27 days long. The draconic month lasts 27.21 days. The calculations are determined when it gets back to a specified point in its orbit.
The tropical month is also about 27 days long. It is measured in terms of the time it gets back to the ecliptic longitude. While the lunar months vary, the time when the full moon occurs will not be that too far from each other.
Checking the Dates
Today there are several calendars or software that help you calculate the time the phenomenon takes place. When using them, always check the dates they use. If a calendar shows the date in a different time zone from your own, it could get confusing. A look at a calendar will show that on June 7 2009 there will be a full moon. However it may be June 6 or 8 in your area of the world.
A lot of the calendars that have been used by various civilizations are based on when the full moon occurs and its other phases. These include the Chinese, Hindu and Mayan calendars. While there are some differences in the days, their calculations and usage of days mean that when the phenomenon occurs, it’s on the usually on the 14th or 15th of the month.
Several feasts and events mark this event, among them Easter and the Chinese Mid Autumn Festival. There are also several myths and folklore surrounding this celestial event. They can be found in legends in various cultures.
Even to this day there are still religious groups that hold special ceremonies when the full moon occurs. Others look forward just to marvel at its beauty. What seems clear is that people’s interest with this celestial event will continue.