A rare Blue Moon will be spotted in the sky on October 31, that is, on Halloween this year. It is being called a Blue Moon because it will be the second of two full Moons to occur in a single calendar month. The last Blue Moon by this definition of the term happened on March 31, 2018.The last time the Blue Moon was spotted on Halloween day, that is, October 31, was in the year 1944.
What is a Blue Moon?
If you are wondering that the colour of the moon will change to ‘Blue’ on October 31, you are wrong! The term ‘Blue Moon’ has nothing to do with the colour of the moon and is used to indicate a second full moon in the same month. The first full moon was sighted on October 1, 2020, and was called ‘Harvest Moon’. The second moon will be sighted on October 31, 2020– on the date of Halloween.
Colours of the Moon
The colour of the rising Moon appears reddish but when the Moon is well above the horizon, it loses that red hue and looks white with many shades of grey. According to experts, this is due to the scattering of light by the Earth’s atmosphere, which is made up of nitrogen (78%), oxygen (21%) and argon (0.9%). The remaining 0.1% of the atmosphere consists of carbon dioxide, methane, water vapour and dust particles. When a ray of light enters the atmosphere, it is scattered in different directions by air molecules. The blue part of the light is scattered the most and the red the least. Closer to the horizon, when the Moon is rising or setting, this light has to pass through a thicker layer of atmosphere than when it is well above the horizon. By the time the ray of light reaches us, most of the blue component is scattered away and only red light remains. So, the rising and setting Moon appears reddish. This phenomenon is also applicable to sunrise and sunset. The scattered blue component of sunlight that is reflected in all directions makes the sky look blue. When the Moon is seen through smoke and dust caused by a forest fire or volcanic eruption, most of the red component is blocked and only the blue rays reach us, giving the Moon a bluish hue.