'What is a blood moon?' and other fun questions about the upcoming apocalypse

The internet's got end-of-the-world fever: here's what's really happening

A 'blood Moon' from 2011. The coppery hue is caused by light from the sun refracting through the Earth's atmosphere and striking the surface of the Moon - it's the same mechanism that makes sunsets and sunrises appear red. (ADALBERTO ROQUE/AFP/Getty Images)

Tetrads, blood moons and the apocalypse: sometimes it seems that there’s just too many mystical-sounding buzzwords floating around not to throw your hands up and start proclaiming the end of days.

At least, this seems to have been the inspiration for apocalypse-mongerers who have been busy greeting a fairly rare (but completely foreseeable) astronomical event as the fulfilment of an ancient prophecy of global catastrophe.

To explain what’s happening as succinctly as possible: on the 15th of April you’ll be able to see the first total lunar eclipse in a series of four (a phenomenon known as a tetrad to astronomers), which will also happen to coincide with the Jewish festivals of Passover and Sukkot in 2014 and 2015.

Lunar eclipses in general are sometimes called ‘blood moons’ because the light bouncing off the moon is refracted through the Earth’s atmosphere giving it a coppery hue (it’s the same mechanism that make sunsets and sunrises look red).

From Revelation 6:12: “I watched as he opened the sixth seal. There was a great earthquake. The Sun turned black like sackcloth made of goat hair. The whole Moon turned blood red."

At some point however, some individuals decided that although on their own these phenomena aren’t incredibly noteworthy, in aggregate they make for a decent bit of apocalypse mongering. Add in some suitably Dan Brown-esque bible soundbites (“The sun will be turned to darkness, and the Moon to blood before the great and dreadful day of the LORD comes”) and you’re halfway to the New York Times’ Best Seller list.

The main culprit in all this is American pastor and author John Hagee, whose 2013 book Four Blood Moons: Something Is About To Change seems to have popularised the notion that four successive ‘blood moons’ is an event of some significance.

“Every time this has happened in the last 500 years, it has coincided with tragedy for the Jewish people followed by triumph,” Hagee told The Daily Express. “And once again, for Israel, the timing of this Tetrad is remarkable.”

The tetrad has previously occured during the Six-Day war between Israel and the neighbouring states of Egypt, Jordan and Syria.

Hagee goes on to say that each of the next four total lunar eclipses will coincide with Passover (15 April in 2014, 4 April in 2015) and Sukkot, otherwise known as the Feast of the Tabernacles (8 October in 2014 and 28 September in 2015).

This is certainly unusual but hardly surprising given that the Jewish calendar is based partly on lunar cycles: Passover is always marked by a full moon and a lunar eclipse cannot – by definition – happen at any other time apart from a full moon.

Writing over at Universe Today, David Dickinson spells it out clearly: “Eclipses happen, and sometimes they occur on Passover. It’s rare that they pop up on tetrad cycles, yes, but it’s at best a mathematical curiosity that is a result of our attempt to keep our various calendrical systems in sync with the heavens.”

Dickinson also notes that tetrads aren’t actually that unusual. They occur when there are four successive total lunar eclipses separated by six month periods, with the Earth placed directly between the Moon and the Sun, first refracting sunlight through the atmosphere onto the Moon (this is what makes it ‘red’) and then blocking all direct illumination (this the actual eclipse).

A composite image showing the various stages of a lunar eclipse from 2007.

However, this isn’t even the first tetrad of this century (that was in 2003-2004) and including this next quartet there will be seven more before the year 2100.

Although it's certainly rarer for all four eclipses to coincide with Passover and Sukkot (this has happened only eight times since 162 CE) it's still a frequent enough occurrence to make events of 'historical significance' happening on the same nothing more than coincidence. Throw a dart at a calendar and you’ll find something of ‘historical significance’ happening on that day - it’s just what history is like.

So, although the thought of watching a good lunar eclipse is pretty exciting (simply head outside on the night of the 15th – no special equipment necessary) the end-of-the-world stuff is about as credible as the Mayan prophecies back in 2012. If you survived them then you’ll probably be A-OK over the next couple of weeks. We promise.