A blue moon is not a moon that appears blue to the eye, but rather a special phenomenon in the astronomical calendar.

On average, blue moons occur once every 2.4 years. Some years have no blue moons, while others have two. When two full moons appear in a single month, the second one is called a "blue moon."

The term "blue moon" does not refer to the moon's color. Instead, it originated in Western countries to describe the fourth full moon that occurs in a season—spring, summer, autumn, or winter. In astronomical calendars and almanacs, when four full moons appear in a season, the third one is given the mysterious and romantic name of the "Blue Moon." While the blue moon is a rare astronomical phenomenon, it is not extremely unusual.

According to the calendar, full moons occur every 29.5 days. However, the Gregorian calendar has 31 days for large months and 30 days for small months, which creates a time difference that allows for two full moons to appear in a single month. On average, a blue moon occurs once every two and a half years.

In everyday life, the phrase "once in a blue moon" has been used since the late 19th century to describe an infrequent event.

NASA scientists, along with the Institute for the Search for Extraterrestrial Intelligence and the British astronomical and biological communities, have used computer simulations to identify two extraterrestrial objects that could exist in the Milky Way galaxy and possibly harbor life. These objects are named "Aurelia" and "Blue Moon." According to scientists, the blue moon has a day that lasts 240 hours and orbits a giant planet. Its atmosphere is four times denser than that of Earth. The high density of the atmosphere and small gravitational force make flight easy, so scientists imagine that "flying whales" could constantly soar in the sky. The concentration of carbon dioxide on the blue moon is 30 times higher than on Earth, which allows a "pagoda tree" to grow up to 1.6 km high.

On the planet Aurelia, as envisioned by astronomers, there are no seasons or day and night. The dark side is covered with ice, while the luminous side has vast rivers and plains due to the presence of the necessary atmosphere for life. Scientists speculate that the most dominant animal on the planet would be an armadillo-like creature, which is present in large numbers in the lake.

NASA launched the Kepler program in 2008, which allowed scientists to search for Earth-like planets orbiting other stars.

Folklore has it that a blue moon is a harbinger of disaster. According to historical records, true blue moons have indeed appeared, often accompanied by disasters. A true blue moon in the night sky is caused by forest fires, volcanic eruptions, and other disasters that produce smoke and dust particles that collect in the Earth's atmosphere and refract light indirectly.

In 1883, the volcano Krakatoa erupted in Indonesia, and the ash drifted high into the Earth's atmosphere, turning the moon blue when people saw it that night. However, the blue moon phenomenon is caused by the natural laws of celestial movement, and its association with natural disasters has no scientific basis.

Astronomers say that people in the United States, Canada, Europe, South America, and Africa can see a blue moon on New Year's Eve. Those in Australia and Asia will not see the full moon until New Year's Day, and they will experience a blue moon in January 2010. Meanwhile, people in the Eastern Hemisphere can observe a partial lunar eclipse on New Year's Eve, while the United States will not see a partial lunar eclipse.