The rare full moon of 2021 shines in our sky this weekend

Set aside a few minutes on Sunday evening to see the night sky. When Jupiter and Saturn are visible from dusk to dawn, Venus will be at night, near the western horizon. As for the full moon, that night will be special: blue and the third in the fourth season.

Blue Moon: An “extra” moon

There are two types of blue moons. The first is visible when there are two full moons in a calendar month. We last saw Halloween in the fall of 2020. Other types of blue moons appear in a season with three full moons per year. But, the full moons of this season happen once in four years or every three years.

This occurs when the first full moon of the season occurs a few days before the start of the season. Then, since the time interval between full moons is only 29.5 days, the next three occur in the previous and respective months. So it will take place before the end of the fourth season. In the summer of 2021, the season begins on June 20 and ends on September 22, so full moons peak on June 24, July 24, August 22 and September 20. Of the four full moons, Sunday, August 22 – This is the blue moon.

NASA visualizes the blue moon on August 22, 2021. Credit: NASA Science Visualization Studio

Is this moon really blue?

The moon star does not have to be blue, it is a transcription of a popular English-speaking expression that represents the rarity of this type of full moon. Often, when we see the moon change color, it will be orange or red. A lunar eclipse may be due when the full moon passes through the shadow of the earth. The shadow is red because when sunlight passes through the atmosphere, air molecules and various dust, particles and water droplets scatter at very short wavelengths of light at first. Thus, only red tones are visible in space.

We can also see this kind of color change when smoke or ash particles are in the air. In this case, the short wavelengths of the moonlight are quickly dispersed, allowing only the orange and red wavelengths. From time to time, we may not always be filled with the idea that the moon is blue, and we can still feel it today. According to NASA, this phenomenon occurs when there are many particles in the air that are slightly larger than the wavelength of red light (0.7 microns) and no other size. It occurs when volcanoes emit clouds like wildfire. The veil formed when viewed from Earth will give the moon a blue color.

See also: Thursday you have never seen!