‘Super blue Moon’ will not appear blue in colour! So, why the name?

The upcoming full Moon set to appear on Wednesday will be a super Moon, a blue Moon, and Rakhi Purnima or Raksha Bandhan – the Hindu festival celebrating the bonds between siblings. However, contrary to the name “blue Moon” – it is known that the celestial body will not actually appear blue in colour. The reason it’s called so is due to the definition introduced by Sky & Telescope magazine in 1946, which defines the blue Moon as the second full Moon in a calendar month.

“The older definition of Blue Moon, dating back to at least the 1500s, is the name for the third full Moon in a season with four Moons. By this definition, the full Moon in August 2024 will be the Blue Moon…Neither of these definitions has anything to do with the colour of the Moon…,” NASA explained on its website.

The rare moon will appear full for three days around its peak, from Tuesday night to Friday morning, the American space agency further said.

‘Super Moon’

The NASA further said though the definitions of what qualify as “super” Moon varies among publications, “but all agree that in 2023 the two full Moons in August qualify”.

‘A real blue Moon’

In the 19th century, blue moons appeared for many days and the reason behind them was Indonesian volcano Krakatoa’s ash.

The sun’s light travels in waves, and different colours of light have different physical properties such as wavelengths. The scattering of sunlight in the atmosphere contributes to the colours we see. When Krakatoa exploded in 1883, some of the ash-clouds were filled with particles about 1 micron (one-millionth of a metre) wide–the right size to strongly scatter red light, while allowing other colours to pass, the NASA said. This led to the moonbeams appearing as blue and sometimes green.

Another similar event occurred in 1983 after the eruption of the El Chichon volcano in Mexico.