A rare event in the skies of Israel: A "mini blue moon" will reach its peak this evening

Around the world and in Israel, people are preparing for a particularly rare celestial spectacle that will take place this evening (Sunday): the "Blue Micromoon." Although the name sounds dramatic and sparks the imagination, the moon will not turn the sky blue, nor will it become a tiny dot. Nevertheless, it is an extraordinary event that occurs only once every few decades.

What is a "blue moon" anyway?

The term "blue moon" has two different scientific definitions, but this time it refers to the most common and simplest version: a calendrical blue moon.

"The most commonly known definition today is simply the occurrence of a second full moon within one calendar month," explained Dr. Greg Brown to The Guardian. An average lunar cycle lasts about 29 and a half days, so usually we see only one full moon each month. "But occasionally, the dates synchronize such that one month contains two full moons, and the second of these is the blue moon."

The second type, called the "seasonal blue moon," refers to a fourth full moon (instead of the usual three) that appears during a single astronomical season (the period between the equinoxes and the solstices).

And what makes it a "micro-moon"?

The second part of the phenomenon concerns the apparent size of the moon in the sky, which is affected by its elliptical orbit around the Earth. The distance of the moon from us is not constant.

"If a full moon occurs when it is at its closest point to us, we call it a 'supermoon,'" noted Dr. Brown. "And if the full moon occurs when it is at its farthest point from Earth, that is a micromoon."

Don’t expect to see a tiny, disappearing dot in the sky: Physics shows that a micro-moon appears only 14% smaller compared to a supermoon, and only about 6% smaller compared to a regular full moon. The average observer will have difficulty noticing the difference without aid, but in photographs the difference is very tangible.

How rare is this combined event?

While a "blue moon" alone occurs on average once every two and a half years, and a "micromoon" appears two or three times each year, the simultaneous combination of both ("mini blue moon") is much rarer and happens about once every 20 years.

Scientists emphasize that due to differences in time zones and the international date line, different regions around the world may not agree on the exact timing. For example, while in the USA and other parts of the world the next occurrence will take place in 2053, in Britain it will only be seen in 2066.

And will it really be blue? The answer is no. The moon will retain its usual white-yellowish color. However, Dr. Brown notes that there is an unrelated atmospheric phenomenon, in which massive forest fires or volcanic eruptions emit dust particles into the air. These particles cause light to scatter and give the moon a bluish tint, and this is apparently where the famous expression "once in a blue moon," denoting a very rare event, originated.