Friday , January 27 2023

A strange “month of blood” appeared on New Year’s Day. Is 2021 destined to be a year of disasters? Use science to break the augury prophecy! -PanSci


On the night of January 1, 2021, many people in the south saw a round, red moon, even shining with a blood-red light. Such a strange color caused many people to panic: “A month of blood appears on New Year’s Day, is it a prediction from 2021? Will this year be a year of disasters? “

Is the celestial phenomenon commonly known as the “blood moon” really a precursor to disaster?

In fact, the blood moon, like the solar eclipse commonly known as the “Tengu Eclipse,” is nothing more than a special astronomical scene. The color myths about the moon are not just the blood months and even the so-called ” blue Moon”. Now, let’s use earth science to reveal the rumors about the blood moon and the blue moon!

That month of red and round blood

Why does the blood month happen? First of all, the “full moon” of the moon phase on that day is one of the reasons why the blood moon hangs in the sky.

The image below shows the relative positions of the sun, earth and moon. The sun and sunlight it emits come from the right side of the image. The earth is in the middle of the image, and the satellites of the earth surround the outer circle of the earth. –Month.

The relative positions of the sun, earth and moon and the phases of the moon we see. Figure / Wikipedia

The first circle on the outer periphery of the earth is the “sunlit surface of the moon.”

Because the volume of the sun is very large in relation to the earth and the moon, and the distance between the moon and the earth is farther than the image, so ifFrom the reader’s perspective, the sun will always shine on the right side of the moon.

What is interesting is that because the speed of the revolution of the moon is similar to the speed of rotation, the moon always faces the earth on the same side.The moon that people on earth see is always the same part!

The outermost circle is the “phase of the moon when people look up” at the earth.

When the relative positions of these three planets are “earth, moon, and sun,” the earth cannot see the sun illuminating the middle of the moon at all, so the lunar phase of the day is the “new moon” and “new moon” we often hear. “(Phase of the month at 3 o’clock in the image above), the time is around the first day of the monthly calendar.

And when they are “moon, earth, sun,” people on earth can see the sun illuminating half the moon, which looks like a round moon. The lunar phase of the day is what we call the “full moon” and the “full moon.” “(Phase of the moon at 9 o’clock in the picture above), the time of the full moon is around the fifteenth of the monthly calendar.

The month whose color gradually changes. Figure / wikipedia

The important thing is that at the full moon, because the relative positions of these three planets are “moon, earth and sun”, most of the sun’s rays “will first pass on the earth and then reach the moon”.

For the month of blood photographed by the public, it can be known from the full moon that it should be around the full moon at that time. After consulting the calendar, it can also be determined that the monthly date of the New Year’s Day is the 18th.

Colored sunlight, composed of different wavelengths

Light is a type of electromagnetic wave. Each celestial body emits electromagnetic waves of different wavelengths. When the wavelength of electromagnetic waves falls in the “visible light” band, we can see the light with the naked eye and light of different wavelengths will appear. different color.

The electromagnetic waveband emitted mainly by sunlight is the visible light waveband. In the visible light waveband, there are seven colors, such as red light with a longer wavelength, to purple light with a shorter wavelength, which are the seven colors of the rainbow we are familiar with.

The position of visible light in the electromagnetic spectrum. Figure / wikipedia

When our eyes receive light with a relatively long wavelength, the colors they see will be biased towards red and orange, on the contrary, the light with short wavelength will be biased towards blue and purple.

Sunlight “reformed” by the atmosphere!

When sunlight passes through the Earth’s atmosphere, it will be absorbed and scattered by air molecules in the atmosphere. Different wavelengths are scattered in different degrees. Short wavelength (blue) electromagnetic bands are easier to scatter, causing a large amount of blue light to scatter in the sky. It is covered with scattered blue light, forming the blue sky we see.

The above-mentioned scattering phenomenon caused by air molecules is called “Rayleigh scattering”.1.

At full moon, much sunlight will pass through the earth’s atmosphere and then reach the surface of the moon. During this process, most of the blue light will be scattered in the Earth’s atmosphere, letting the short-wavelength red light move forward, and eventually the red light will be refracted to the moon’s surface. It will make the surface of the moon look reddish.This is the cause of the bloody moon.

It can be seen that, in fact, each full moon will be more or less illuminated by red light, but in different circumstances, sometimes the color red is very obvious, and other times it is not so obvious.

For example, when there is a total solar eclipse, because almost all of the sunlight will be blocked by the earth, only long-wavelength red light can be refracted from the atmosphere to the moon’s surface, making the moon appear obvious red. .

All in all, the blood moon is not a precursor to disaster, but just a normal natural phenomenon!

In the shadow area is a total lunar eclipse, the earth will block all direct light from the sun and only red light can be refracted to the surface of the moon, showing a red moon; in the penumbra area, only part of the sun is blocked, ie partial or penumbral lunar eclipses. Figure / wikipedia

Not the bloody moon of the full moon, the red and red sunset

Although bloody months often occur during the full moon and lunar eclipses, there are other conditions that affect the color of the moon’s surface.

If the moon’s height angle is low, visible light will pass through a thicker atmosphere, making it easier for blue light to scatter into the atmosphere, making it more likely to see the red moon near ground level or when there is too much particles in the air. You may also see a reddish moon in the sky,

But in both cases, the “scatter” is the main reason why the moon looks red!

The orange sunset we see during the week is similar! As the sun gets closer and closer to the horizon, the thicker the atmosphere through which the sunlight passes, the more blue light will be scattered, becoming redder as the sun approaches the horizon.

The beautiful sunset also comes from the scattering! Photo / Pixabay

If there were other smaller particles in the atmosphere besides the air particles at that time, the smaller the particles, the stronger the scattering effect and a large number of particles reflecting red and orange light, which would make and the sky to look beautiful.

The blue moon is not the blue moon!

In addition to the blood moon, we also occasionally hear the “blue moon”.

Whenever the blue moon appears, the media or social networking sites will rush to report and add a big blue photo of the moon, so many people will wait to see the blue moon in the sky.

As everyone knows, Blue Moon is not a “blue moon” at all! The blue moon refers to the phenomenon of the “second full moon” in a month.

We are accustomed to consider the time that the moon revolves around the earth as a month, the big moon has 31 days and the small moon has 30 days, but in fact, the cycle of the moon orbiting the earth is 29.5303 days, the number of complete days of each month The time difference from the actual number of days is about 0,5303 days.

As the time difference between the two gradually accumulates, after every 2-3 years, there will be a full moon in a certain month, and this additional full moon is called the “blue moon”.

The volcano erupts, allowing you to see the true blue moon

Although the blue moon reported in the regular news does not refer to the “blue moon”, but occasionally, we can actually see a slightly blue moon.

During a violent volcanic eruption or forest fire, the air will be filled with suspended particles produced by volcanoes or fires. These suspended particles are larger in size and more numerous than usual. When they fill the atmosphere, they will cause the longer wavelengths of red, orange and yellow light to produce a lot of scattering and we call this scattering “scattering Me”2.

Mount St. Helena, Washington, USA, erupted on May 18, 1980. Figure / wikipedia

Because long-wavelength light is scattered widely, the moon will appear blue at that time. During the eruptions of Mount St. Helena in 1980 and Mount Pinatubo in 1991, people saw the true blue moon in the night sky. .

What are the special meanings of the blood moon and the blue moon?

Whether it’s a bloody month or a blue moon, everyone is given special meanings because they are very rare, and different cultures have many different interpretations of them.

Most cultures believe that the red moon has an ominous meaning. When the blood moon appears, there will be a disaster of blood and light. Therefore, when people see the blood moon hanging in the sky, they associate it with disasters.

The occurrence of blue moons is relatively rare, so foreign countries often use “Once a blue moon” to describe less easy or less frequent events.

  • Editor’s note: if you search “once in a blue month” on Google, you’ll get the frequency of the blue month: 1.16699016 × 10-8 Hz.
Look for “once in a blue month.”

I hope that when you hear the bloody moon or the blue moon in the news, you can remember their true cause and not make it ugly to turn people into a symbol of evil and disaster! Let’s fill our lives everywhere with the science of the earth!


  1. Rayleigh scattering: the scattering phenomenon that occurs when the particle size is less than 1/10 of the wavelength, such as visible air molecules and light bands.
  2. Scattering Me: Scattering when the particle size is equal to or greater than the wavelength, such as water droplets, pollutants and visible light.

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