Familiar with the phrase “once in a blue moon?” well, the meaning embedded in the phrase is quite literal in the astronomical sciences although it does not have its roots in the discipline. By contemporary definition, a blue moon is a phenomenon where there are two full moons within the span of a month. The original
definition, however, states that the blue moon is the third of four full moons in a season. By virtue of the contemporary definition, we can begin the countdown as we expect to sight
the Blue moon on July 31 2015.
The disparity between the moon’s orbit and months in our calendar is responsible for this astronomical marvel. On average, it takes the moon about 29 days to wax and wane through its four
different phases. Except for February, most months have more than 29 days, which logically explains the phenomenon of two full moons within the same month. The first full moon sighting for July 2015 was on the 1st, we will have the blue moon on July 31 2015,which will be the second full moon of the month.
Blue moons do not occur every year. As a matter of fact, a study of lunar calculations over time reveals a 2.7 year gap, with small deviations between blue moons. It is also not uncommon to have two blue moons within the same year. The last double blue moon year where there were two months, January and March with blue moons was in 1999,while 2018 is the next year where the phenomenon of double blue moon is expected. It is important to understand that while the concept of “blue moon” relates to the rarity of the phenomenon, there are instances when the moon is literally blue in color. The moon, full or in any of its other phases may appear blue after an ash volcanic eruption, dust storm or forest fire when the atmosphere is packed with smoke and dust particles of different shapes and sizes slightly less than 1.0 omicron in width. In addition, the blue appearance of the moon is attributable to the integration of ice crystals to form a ring around the moon on some cold winter nights.
Depending on the timing of the blue moon, it is suffice to say some places in the world will not technically experience the phenomenon due to the technicalities that time zones represent. Different time zones may experience the blue moon at different times, and in some cases during different months.