Lunar calendars are based on the lunar cycle, which goes as follows: new moon » first quarter » full moon » last quarter » new moon. In these calendars, a month refers to the period between two full moons or two new moons, depending on which lunar calendar is taken into consideration. In the Hindu calendar, for instance, the month starts with a full moon and ends with the next full moon. In the Chinese lunar calendar, in contrast, the month starts with a new moon and ends with the next new moon.
Once in a Blue MoonWe often use the phrase 'once in a blue moon', but did you know that the term 'blue moon' actually refers to the second full moon of a calendar month?
While most of us use the Gregorian calendar, there do exist some communities which use the lunar calendar or moon phases calendar even today. The Islamic calendar (or Hijri calendar) consisting of 12 lunar months is one of the best examples of the same.
Full Moon Days of 2015
Before we get into the details, you need to note that the time mentioned here is the Coordinated Universal Time (UTC). You might have to refer to the UTC offset to convert it to your local time. In North America, for instance, the Eastern Standard Time (EST) is UTC−05:00/UTC−04:00 (DST) and Central Standard Time (CST) is UTC−06:00/UTC−05:00 (DST).
Phases of the Moon Explained
In order to understand how lunar calendars work, you need to get well-versed with the different phases of Moon; the full moon and new moon in particular. The four major phases of the Moon are ...
An illustration of the lunar cycle.
Basically, a new moon occurs when the Sun, Moon, and the Earth come in a straight line with the Moon in between, in such a manner that its dark side faces the Earth. As a result of this, it is not visible to the naked eye when seen from the Earth on a new moon day. The full moon, on the other hand, occurs when the Earth is in-between the Sun and Moon. In this case, the Sun's light gets reflected on the Moon, and the side facing the Earth gets illuminated, thus making it appear very bright.
The full moon doesn't occur on the same day of every month as the Moon takes 29½ days, and not specifically a month, to orbit the Earth. (Due to this, we witness two full moons in a single calendar month every three years.) It's precisely because of this that the month of February may not have a full moon at times. The last time it happened was in 1999. The next time it will happen will be in 2018.
On the day of the full moon, it is at its best, appearing very bright and full from the planet. On a new moon day though, it appears as if there is no moon in the sky, unless you use a telescope to get its glimpse.