‘Super blue blood Moon’ lights up the sky

West to East: The Moon rises over hills in Vladivostok in Russia's Far East. © Getty

Why are coincidences so interesting? Yesterday morning a large, reddish Moon heralded an incredibly rare celestial convergence. What do coincidences say about the way we think?

For the first time in 152 years yesterday, star-gazers in North America, as well as parts of Asia and the Pacific, were treated to the rare site of a super blue blood Moon.

It sounds apocalyptic, so let’s break it down into its component parts.

Super. A supermoon is when the Moon is full at the same time as its perigee — the closest point of the moon's orbit to Earth. The result is that the moon appears larger than normal. NASA is predicting this one will be 14% brighter than usual.

Blue. You will know the phrase “once in a blue Moon”. The idiom refers to the instance when there is a second full moon in a calendar month. The last full moon took place on January 1st.

Blood. A blood Moon is the moment during a lunar eclipse when the moon, in the Earth’s shadow, takes on a reddish tint.

Taken individually, none of these events are especially remarkable. Combinations of two, such as a super blue Moon, are reasonably rare. But the three happening simultaneously is a genuinely extraordinary coincidence. A super blue blood Moon has never been photographed.

People react in many different ways to coincidences, but most share “a feeling that the fabric of life has rippled”, in the words of Julie Beck in The Atlantic.

Some are almost unbelievably unlikely. The author Mark Twain was born on the day of the appearance of Halley’s Comet in 1835, and died on the day of its next appearance in 1910.

In the 1920s three Englishmen were travelling on a train in Peru. One man’s last name was Bingham, and the second man’s last name was Powell. The third man announced that his last name was Bingham-Powell. None were related in any way.

“What are the chances of that?” Well, very low. But then, as the statistician David Hand says, “Extremely improbable events are commonplace,” given the huge number of things that happen on Earth. Picking six correct lottery numbers is an incredible coincidence. But we take it for granted that someone, somewhere will.

So why are we so entranced by coincidences?

Beating the odds

Their sheer unlikeliness, reply some. Simply trying to work out the infinitesimal chance of a super blue blood Moon happening is fascinating. The surprising regularity of coincidences reminds us of the vastness of reality, while also making the world seem very small indeed.

They are interesting because of what they say about us, others respond. People can be very liberal when they think about coincidences — you might consider it a coincidence that another friend shares your birthday, even though this is quite likely. Coincidences are remarkable in how they straddle science and belief. People have surprising experiences, and they are desperate to find meaning out of them.

You Decide

  1. Why are coincidences so interesting?
  2. Is probability the most important branch of maths?


  1. Find a famous historical coincidence and try your best to work out the probability of it happening.
  2. Each person in the class describes the most extraordinary coincidence which has happened to them. Take a class vote on whose story was the most unlikely.

Some People Say...

“A coincidence is in the eye of the beholder.”

Professor David Spiegelhalter

What do you think?

Q & A

What do we know?
Yesterday an extremely rare celestial event took place. It has been dubbed a “super blue blood Moon” and combines three unusual, yet relatively common happenings. People experience coincidences all the time, and react in different ways to them. We can be certain that, due to the vastness of humanity and the universe, many outrageously unlikely things do in fact happen.
What do we not know?
Whether humans will ever overcome their incredulity at coincidences, given that they are bound to happen thanks to the laws of probability. Many scientists believe that confirmation bias (which means we interpret what happens in the light of what we already know) is deeply ingrained in our psyche, and that we will never be able to look at coincidences completely rationally.

Word Watch

North America, as well as parts of Asia and the Pacific
Unfortunately the occurrence will not be visible from Britain as it will be below the horizon. Americans on the US west coast will be able to see the eclipse in the small hours before sunrise, while people in Asia and the Pacific will see it later in the day.
The most recent supermoon took place on December 4th 2017. It was the only such event of the year and was visible in much of the United States.
Blue Moon
It occurs, on average, every two and a half years, although there will be two blue moons in 2018, one yesterday and one on March 31st.
Lunar eclipse
This occurs when the Moon passes directly behind the Earth into its shadow. It can happen only when the Sun, Earth, and Moon are aligned in "syzygy", with the Earth in the middle.
Mark Twain
Most famous for writing The Adventures of Tom Sawyer and its sequel, The Adventures of Huckleberry Finn.
Halley’s Comet
A comet which is visible from Earth every 74-79 years. It will next be sighted in 2061.

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