Image credit: Pixabay/jeanvdmeulen
Image credit: Pixabay/jeanvdmeulen
The blood Moon, or blood wolf Moon, will be at its closest point to Earth in its elliptical orbit around our planet on 20 and 21 January. It will also be the last total lunar eclipse visible for the next two years.
The next total eclipse will grace us with its majestic beauty on 26 May 2021 and only from Europe. So, make sure you don’t miss out this Monday!
If you do miss it, you’ll have to make do with a few partial lunar eclipses over the coming years, but that’s not really the same. Total eclipses happen only when the Earth moves precisely between the Sun and Moon. A partial lunar eclipse occurs when the Sun, Earth and Moon are not perfectly aligned.
The term “blood Moon” has evolved over the years. It used to refer to a series of four total eclipsed Moons in a row. Also known as a lunar tetrad. Two Christian pastors used the phrase in a book about an upcoming lunar tetrad which would bring about the apocalypse.
Before that, it was another name for a Hunter’s Moon. Different types of full moons have different names: Wolf Moon in January, Snow Moon in February, Worm Moon in March, and so forth. Hunter’s Moon occurs in October. But it’s not red.
Today, the term blood Moon is simply used to describe the phenomenon when the Moon eclipses totally and appears reddish in colour.
The short answer is that the red hue occurs when the sunlight filters through Earth’s atmosphere and gets refracted in the process.
Because the Moon does not have any light of its own – it only reflects the sunlight – the moon’s light supply will get cut off when the Earth moves between the Sun and Moon. Due to this, the Moon’s surface takes on a red glow before it goes completely dark.
Why red, you ask? This is where it gets complicated. The red hue is due to a phenomenon called “Rayleigh scattering.” It’s the same phenomenon that gives sunrises and sunsets its orange hue, and the reason why the sky in daylight appears pale blue.
The official scientific explanation for Rayleigh scattering: “Rayleigh scattering, named after the British physicist Lord Rayleigh, is the predominantly elastic scattering of light or other electromagnetic radiation by particles much smaller than the wavelength of the radiation. Rayleigh scattering does not change the state of material and is, hence, a parametric process.”
Well. Now you know.
Another reason it goes red is Earth’s atmosphere. When sunlight enters our atmosphere, it hits all the particles that are smaller than the light’s wavelengths. (You know now that it’s called Rayleigh scattering.) Because not all particles are scattered equally, colours with shorter wavelengths, the blue hues, are removed from the sunlight.
The red wavelengths then pass through our atmosphere, is refracted around our planet before it hits the moon’s surface during an eclipse. Only a fraction of the blue wavelengths will make it through, and these can sometimes be observed right at the beginning and the end of the eclipse, as can be seen in this image:
First, we need to look at the three distinct parts of a shadow created by a light source: Umbra, penumbra and antumbra. Umbra is the innermost darkest part of a shadow where the light source is completely blocked.
Penumbra is the region where only a portion of the light is obscured. The antumbra is the lighter part of the shadow that forms at a certain distance from the object casting a shadow.
So, on 20 January, the Moon will enter the Earth’s outer shadow, known as the penumbra. This is the phase where the Moon will “lose” its brightness. Then, it will enter Earth’s central shadow where it will become partially eclipsed. The Moon will only take on its red hue when it eclipses totally.
The views from Earth will be spectacular, but it’s a pity we’re not on the Moon this January. If we were on the Moon as Earth began to block the sun’s light, it would be completely dark with a ring of bright light in the darkened sky above.
The sunlight will illuminate the rim of the atmosphere around Earth. In essence, while we are observing a lunar eclipse, someone stationed on the Moon – Lunarian? Mooninite? – would be witnessing a solar eclipse.