Skywatchers are in for a rare astronomical spectacle as a Blue Moon is set to light up the night sky this weekend (May 31). Visible across several parts of the world, including India, the event is expected to offer a breathtaking view during dusk and moonrise.
Contrary to its name, the Moon will not actually appear blue. Instead, a Blue Moon refers to the second full Moon occurring within a single calendar month, a rare event caused by the mismatch between the Moon's cycle and the calendar.
The lunar cycle spans approximately 29.5 days, slightly shorter than a typical month. Because of this timing difference, an extra full moon occasionally appears, earning the title "Blue Moon." This rare occurrence is also the origin of the popular phrase "once in a blue moon," used to describe something that happens infrequently.
Why This Blue Moon Is Special?
This weekend's celestial event comes with an added twist - it will also be a micromoon, meaning the Moon will be near apogee, the farthest point in its orbit from Earth.
Since the Moon's orbit is not perfectly circular, its distance from Earth changes throughout the month. As a result, this Blue Moon will appear slightly smaller than usual, though experts say the difference may be difficult to notice with the naked eye.
According to NASA, the Moon will be approximately 252,334 miles away from Earth, compared to its average distance of about 238,855 miles, making it the most distant full micromoon of the year.
Interestingly, the last calendrical Blue Moon in 2023 was the exact opposite - a supermoon, which occurs when the Moon reaches perigee, its closest point to Earth.
When and Where to Watch in India
For skywatchers in India, the Blue Moon will be visible on Saturday evening, May 30, during dusk. At moonrise, the Moon is expected to appear larger and glow with a warm orange hue near the horizon, gradually transforming into its familiar bright white colour as it climbs higher into the sky.
Experts suggest moonrise - typically between 5:30 p.m. and 6:30 p.m., depending on location - as one of the best times to witness and photograph the event, especially while the sky still holds soft evening blue tones.
Can the Moon Actually Turn Blue?
Although extremely rare, the Moon can occasionally appear blue under unique atmospheric conditions. Scientists say that when smoke or dust particles in Earth's atmosphere are slightly wider than 900 nanometres, red wavelengths scatter, making the Moon look bluish.
One of the most famous examples occurred in 1883, when people reported seeing a blue Moon following the eruption of Indonesia's Krakatoa volcano.
A Rare Celestial Calendar Event
A year can sometimes witness two Blue Moons, though such events are uncommon. The last instance happened in 2018, when both January and March hosted two full moons, while February had none. The next occurrence of this unusual calendar pattern is expected in 2037.
Astronomers also recognize a seasonal Blue Moon, which happens when four full moons appear within a three-month season instead of the usual three. The next seasonal Blue Moon is expected on May 20, 2027.
Highlights:
Blue Moon visible in India on May 30 during dusk
Second full Moon in a calendar month
Will also be a micromoon - the farthest full micromoon of the year
The moon may appear orange at moonrise before turning white
Next rare double Blue Moon year expected in 2037
