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What is the blue moon? : Shortwave: NPR



On January 31, 2018, in San Francisco, California, a partially dimmed super blue blood moon is behind the Golden Gate Bridge. The “Super Blue Blood Moon” is a rare “Triple Moon” event, the first such lunar event in North America since 1

866.

Justin Sullivan/Getty Images


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Justin Sullivan/Getty Images

On January 31, 2018, in San Francisco, California, a partially dimmed super blue blood moon is behind the Golden Gate Bridge. The “Super Blue Blood Moon” is a rare “Triple Moon” event, the first such lunar event in North America since 1866.

Justin Sullivan/Getty Images

This year, Halloween will be full moon. This is the “Blue Moon” because it is the second occurrence in the same calendar month. This phenomenon usually occurs every 2.7 years. This may mean that events that occurred in “A Blue Moon” are actually not that rare.

However, the blue moon we know and love (two full moons can be seen in a month) is a relatively new definition.

As planetary scientist Corrine Rojas explained, the term “blue moon” usually refers to the third of the four full moons that occur in a season, especially the moon “between the vernal equinox and the winter solstice of the year.” This is because astronomers define seasons in terms of the vernal equinox and the highest point, rather than the three-month block used by meteorologists.

According to earthsky.org, this shift from a seasonal blue moon stems from oversimplification in 1946 Sky and telescope magazine. This error was obviously amplified in the radio show “StarDate” and later “Trivial Pursuit”.

In both cases, there is an additional moon.

To understand why both moons occur, understanding the lunar cycle is the key. It is shorter than most calendar months and only lasts about 29.5 months according to the religious council cycle. Therefore, it will eventually be the second full moon in the same calendar month.

More rare? It actually looks like a blue moon.

For the moon appear Blue is another matter. A specific substance of sufficient size must be kicked into the atmosphere to scatter the red light. The most popular example is the eruption of the Indonesian volcano Krakatoa in 1883. According to NASA, the eruption was so big that after many years, The moon appears bluish, sometimes green. The volcanic ash particles are large enough to block red wavelengths, while other wavelengths continue as usual.

Yellow moons are more common. When the moon is close to the horizon, the sunlight that illuminates the moon must spread farther. Along the way, blue wavelengths are scattered, leaving longer, redder wavelengths.

However, all of these are nothing more than lightness. Rojas said: “The moon will maintain the beautiful, brilliant colors we know and love.” Those are gray and white-just like the moon tomorrow.

For Rojas, the moon is beautiful regardless of the shadow. “I have always liked staring at the moon. I call it my first love.”

Other resources:

Follow Maddie and Rebecca on Twitter to get more scientific knowledge.McGrady @maddie_sofia And Rebecca’s @rebeccalramirez. Send you your celestial meditations and inquiries via email.we are at shortwave@npr.org.

This episode was produced by Thomas Lu, edited by Viet Le, and checked by Ariela Zebede.




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