This Halloween is a ‘once-in-a-blue-moon’ event as it happens to be the night the rare Blue moon will appear in the sky. However, unlike Blood moon or Red moon, the Blue moon isn’t named for its colour, therefore, one must not expect a giant blue orb in the night sky.
While full moons occur every month, which brings the total to 12 full-moons a year, some full moons are more special than others.
The Blue moon is generally the third full moon of a season. However, NASA says there is a myth around the blue moon where most people wrongly assume it’s the second full moon of the month. However, due to widespread cultural influence, now both of these full moons- third of a season and second of a month- are considered as ‘Blue moons.’ The one to show up in the night sky today is the monthly kind; as there was already a full moon on October 1 (Or October 2 in other time-zones). And this year’s Blue moon is extra special as it’s extra rare to have this full-moon on Halloween night! The last time this happened was in 1955.
It will also be visible globally, another rare event. The 1955 Blue moon on Halloween wasn’t visible in Western hemisphere countries like the USA.
But why call it a blue moon? Well, it may be traced back all the way to late 1800s when a volcano exploded in Indonesia, expelling tall plumes of darken ash clouds into the lower atmosphere. The particles may have scattered red light away (if you remember high school Physics, “white” light is made up of all the visible spectrum colours). Because of this, a blueish tinge dominated the sky and the full moon appeared blue in colour.
The rare event gave rise to the saying- one in a blue moon- as in something that is rare to occur.
Just like leftover day hours keep adding up to give us February 29; the twelve moons are separated by 29.5 days. The half a day adds up once a year to give us a rare month with two full moons- every once in a blue moon.
While the Blue moon on October 31 will be bright, white and silvery, there still might be a chance for a blueish tint in certain atmospheric conditions. Be ready to view it any time after 8:15 pm IST.