The moon on Sunday, when Indians will celebrate the festival of Raksha Bandhan, will be a blue moon, the American Astronomical Society has predicted. Contrary to what folklore tells us the moon does not actually turn blue on such nights but rather a ‘blue moon’ is the third full moon in a season containing four full moons, rather than the usual three, according to Sky & Telescope magazine.
Read on to find out more about this rare event:
1. The terminology was once inaccurately interpreted by amateur astronomer Hugh Pruett, who incorrectly assumed that the definition provided in the Maine Farmers’ Almanac meant blue moons refer to the second full moon in a month. Pruett, who was a regular contributor to Sky & Telescope magazine, helped popularise this modern-day definition but the magazine admitted the mistake in their March 1999 issue.
2. The National Aeronautics and Space Administration (Nasa), however, believes that there are two types of blue moons-monthly and seasonal. Pruett’s definition of a blue moon is what Nasa terms the monthly blue moon. “A monthly Blue Moon is the second Full Moon in a calendar month with two Full Moons. Then, there’s a seasonal Blue Moon – the third Full Moon of an astronomical season that has four Full Moons,” the federal space agency wrote in a blog post on their website.
3. Editors and contributors to Sky & Telescope continue to use the term blue moon to define the third full moon in a season of four full moons. “Introducing the ‘Blue’ Moon meant that the traditional full Moon names, such as the Wolf Moon and Harvest Moon, stayed in (sync) with their season,” said Diana Hannikainen, Sky & Telescope’s observing editor, in a news release.
4. The term ‘Blue Moon’ does not mean the moon changes its colour that can happen only due to water droplets in the air, certain types of clouds, or particles thrown into the atmosphere by natural catastrophes, such as volcanic ash and smoke, and that’s an extremely rare event. “Blue-colored Moons appeared for years following the 1883 eruption (of the Indonesian volcano called Krakatoa). Many other volcanoes throughout history, and even wildfires, have been known to affect the color of the Moon. As a rule of thumb, to create a bluish Moon, dust or ash particles must be larger than about 0.6 micron, which scatters the red light and allows the blue light to pass through freely. Having said all of that, what we call a Blue Moon typically appears pale grey, white or a yellowish color – just like the Moon on any other night,” says Nasa.
5. This Sunday might be your one chance to catch a ‘once in a blue moon’ event as the next one will happen in August 2023.