A Blue Moon appeared in the sky over Guangzhou on the nights of August 21-22, 2021! Through the video, you can watch a full moon passing by the Canton Tower in the night sky. This full moon is very special, it is a seasonal Blue Moon!

There are two different types of Blue Moon. The seasonal Blue Moon is the third full moon in an astronomical season with four full moons. The monthly blue moon is the second full moon in a calendar month with two full moons.

Photo: Nanfang Daily

Is the moon really blue?

The words "once in a blue moon" usually refers to something that rarely happens. The blue moon rarely appears in the night sky, which gave rise to this phrase. But what is a Blue Moon?

A blue moon is extremely rare, it has nothing to do with the calendar or moon phase, and it does not have to be a full moon. The blue color of the moon is the result of particles being thrown into the atmosphere by water droplets in the air, certain types of clouds, or natural disasters (such as volcanic ash and smoke). In addition, the blue moon in the photo was processed with a special blue filter or post-processing.

Two types of blue moons

Seasonal Blue Moon: An additional full moon that occurs during an astronomical season. Three full moons usually occur in one season. If there are four full moons in a season, then the third full moon (not the fourth one) in the season may be called the Blue Moon.

Calendar Blue Moon: The second full moon in the calendar month. The moon needs about 29.5 days to complete a phase cycle. If the full moon occurs on the first day of the month, there will be a second full moon at the end of the month. Then the second full moon is also called the Blue Moon (except February).

The next calendrical Blue Moon will happen on August 30, 2023, as the second full Moon in that month. The next seasonal Blue Moon after this is also known as a Sturgeon Blue Moon. It will take place on August 19/20, 2024.

Photo: Nanfang Daily

The following seasonal Blue Moon:

1) August 19, 2024

2) May 20, 2027

3) August 24, 2029

4) August 21, 2032

5) May 22, 2035

6) May 18, 2038

7) August 22, 2040

Source: NASA, timeanddate, EarthSky

Photo: Dong Tianjian, Luo Yifei

Author: Alice