There will be a 'blue moon' this month.

Astronomy enthusiasts are about to witness the first "blue moon" in nearly two years, the second full moon in a month.

'Blue Moon' is coming

The blue moon will appear at the end of July. Photo illustration: Moms Clean Airforce

According to UPI, this July there will be two full moons, the first on July 2, and the second will appear on the last day of the month, July 31.

"Blue moon" is an English term used to refer to the phenomenon of a full moon occurring twice in a month, but it does not mean that the moon emits blue light. Some documents recorded that the moon was blue in 1980 and 1991 due to air pollution (dust particles scatter blue light, making us see the moon as blue).

The last "blue moon" appeared at the end of August 2012. It is predicted that it will be three years from now, in January 2015, before astronomy lovers around the world will be able to admire this phenomenon again.

"Blue moons" exist because the months in the Gregorian calendar do not coincide with the months in the lunar cycle. Normally, each year has 12 full moons corresponding to 12 months. But because the moon revolves around the earth in 29.5 days; while the months in the solar calendar have 30 or 31 days, each solar year has 11 more days than the lunar year. Therefore, after about 2-3 years, there will be a lunar year with 13 months, corresponding to 13 full moons.

According to Vnexpress.net