A pretty rare astronomical event known as a ‘blue moon‘ will be happening on Friday, July 31 ~ tonight.
But why is it called a blue moon? Every month has a full moon, but since the lunar cycle takes 28 days, it doesn’t line up precisely with calendar months. Therefore, every three years, we get a second one in the same month.
Peter Drew said:
A blue moon occurs when two full moons can be seen in the same month of a given year.
As the moon’s period is 28 days it is possible for this to happen in any month other than February which is too short a duration.
Due to the moon’s orbit this phenomenon doesn’t happen every qualifying month so the occurrence is infrequent, the last one was on August 31, 2012.
Needless to say, the moon will not appear blue, it’s the frequency that causes the interest.
However, the moon does take on a bluish hue, but this phenomenon only occurs when there are large quantities of smoke or dust particles — such as during a huge volcanic eruptions — in Earth’s atmosphere.
Often, when the Moon is hanging low, it looks red for the same reason that sunsets are red,
NASA said on their website.
The atmosphere is full of aerosols much smaller than the ones injected by volcanoes. These aerosols scatter blue light, while leaving the red behind.
An example of blue moon happened in 1883 when the Indonesian volcano Krakatoa erupted, spewing so much ash into the atmosphere that the mooon took on a cerulean tinge for years, night after night.
The term ‘blue moon’ can be attributed to Sky and Telescope writer back to 1946, who posited the phrase “once in a blue moon” which was used to refer to the rare occurrence of an extra moon in a month.
This astronomical phenomenon will happen again in January 2018. So, don’t forget to take a look outside tonight.
Ps: We encourage people to share their best moon photos on our facebook’ page.