3 min learnDelhiUp to date: Might 21, 2026 01:48 PM IST
Now we have typically heard the idiom “as soon as in a blue moon,” which suggests one thing that’s vanishingly uncommon. However blue moons should not as uncommon because the idiom suggests.
On Might 1, the sky supplied us a full moon. One other will seem on Might 31 this yr, making Might 2026 a real blue moon month.
The calendar is formed by two totally different cosmic cycles: the lunar cycle, primarily based on the Moon’s orbit across the Earth, and the photo voltaic yr, primarily based on the Earth’s orbit across the Solar. The 2 cycles don’t align completely. A calendar yr is round 11 days longer than 12 lunar cycles.
Over time, this hole accumulates, sometimes leading to two full moons occurring inside a single calendar month. This phenomenon seems roughly each two to 3 years. Underneath the trendy definition, the second of those two full moons is named a blue moon.
Two definitions
The time period “blue moon” has existed for hundreds of years, however the fashionable definition turned standard in 1946 when author James Hugh Pruett misinterpreted outdated copies of the Maine Farmers’ Almanac and described a blue moon because the second full moon in a calendar month. That definition is the one mostly used at this time.
The older definition is barely totally different. Astronomers check with it as a seasonal blue moon, which happens when an astronomical season comprises 4 full moons as a substitute of the standard three. In that case, the third full moon of the season is named a blue moon. The subsequent seasonal blue moon will happen on 20 Might 2027.
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So why name it blue?
The identify “blue moon” has nothing to do with the Moon’s precise color. In contrast to white, gold, or orange moons, whose look will depend on how moonlight travels by way of the Earth’s environment, a blue moon is just a calendrical time period.
The longer the gap moonlight travels by way of the environment, the extra particles scatter sure wavelengths of sunshine, affecting the Moon’s obvious color.
When the Moon actually turned blue
One of many uncommon events when the Moon genuinely appeared blue adopted the Krakatoa eruption in 1883. The catastrophe killed greater than 36,000 folks, principally because of the tsunamis it triggered.
The large eruption despatched large portions of smoke and dirt into the environment. Some particles had been roughly 1 micron huge, a measurement able to scattering crimson mild whereas permitting blue mild to cross by way of extra simply.
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For a number of years after the eruption, observers around the globe reported seeing a bluish Moon within the night time sky.
Among the many broadly shared fashionable pictures of a blue moon are pictures captured through the blue supermoon of August 2023 by Indian photographer Soumyadeep Mukherjee in Kolkata and by Taranjot Singh in Sydney.
For skywatchers in India, the blue moon on 31 Might 2026 will rise within the jap sky shortly after sundown, and will probably be seen with out a telescope.
(This text has been curated by Seekriti Saha, who’s an intern with The Indian Categorical)
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