On Friday we will witness the rare blue moon phenomenon which inspired the saying “once in a blue moon” that describes rare events. The blue moon is the extra moon which occurs in a year. Earth normally has twelve full moons: one for each month. However some years happen to have 13 moons, just like 2015 has now.
Even though the name of the phenomenon has nothing to do with the color the moon and the way in which is lights up the night sky is very beautiful. Even though the full moon appears to last whole night it is actually an instantaneous event which takes place at the moment when the moon, the Earth and the sun fall close to a straight line. Irrespective of the fact that the moon is above or below the horizon the event takes place at the same instant anywhere in the world. The blue moon on Friday, July 31 will take place at 6:43 a.m. EDT (1043 GMT).
The genuine color of the moon is still grey as we already know it from various pictures. If the moon ever seems to have a different color it would be due to events which take place on Earth and not in space. And the moon can only become blue only if particular air compounds like ash and pollutants are in the atmosphere of the Earth. This is possible in volcanic areas.
A real blue moon actually occurred when the Indonesian volcano Krakatoa erupted in 1883. Because of the plumes of ash which reached the atmosphere of the Earth the moon seemed to be blue and at times even green. According to Volcanologist Scott Rowland from the University of Hawaii the sun itself had a lavender hue.
A blue moon occurs on average every 2.7 years and it represents the second full moon which occurs in one calendar month. On July 2nd we had the first full moon. A hundred years ago the concept of blue moon would have had a totally different meaning and be the equivalent of a supermoon. The blue moon from Friday will most likely not be blue since it is after all only a spin-off between the calendar month and the lunar month, but it will still be a beautiful sight to enjoy.
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