Preachers believe passages from the books of Acts and Revelation suggest the blood moon will accompany an ever-approaching end of days.

The 21st century's longest lunar eclipse will last almost two hours on July 27 and the moon will have a spectacular red tinge.

While stargazers enjoy the dazzling phenomenon, doomsdayers will be preparing for armageddon.

The theory was originally made famous by Christian ministers John Hagee and Mark Biltz who said the ongoing "tetrad" – four consecutive lunar eclipses which began in April 2014 with six full moons in between – is the indicator of the end of earth as described in the Bible in Acts 2:20 and Revelation 6:12.

However the tetrad ended in September 2014 and we're all still here.

The end-of-days preachers insist some sort of tragic event is set to hit earth and possibly wipe it out.

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The theory has been picked up by similar thinkers and the prophecy resurfaces weeks before every blood moon.

The "blood moon" theory is interpreted from the Book of Joel, which says: "The sun will turn into darkness, and the moon into blood, before the great and terrible day of the Lord comes."

A similar passage in the Book of Revelations reads: "And I beheld when he had opened the sixth seal, and, lo, there was a great earthquake; and the sun became black as sackcloth of hair, and the moon became as blood."

But it has been routinely dismissed by astronomers and other experts as a myth.

Scientists say the red tinge is due to Rayleigh scattering of sunlight through the Earth's atmosphere.

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It also causes the reddening of the sun at sunset.

Even though the myth has been debunked, YouTube is littered with videos from doomsdayers predicting the end of the world in just a few days time.

Endtime Ministries' Irvin Baxter, who has made a number of failed predictions since the mid-1980s, is among those who point to passages in the Book of Joel.

He has said: "The Bible teaches that end event is coming just ahead of us now and that will be the greatest prophetic fulfilment in the last 2,000 years."

The total lunar eclipse – when the moon passes behind Earth and into its shadow – will last one hour and 43 minutes over July 27 and 28.

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It will be visible across much of Europe and Asia, and in Australia, southern parts of North America, and South America.

Of course the warning about the upcoming rapture is the latest prophecy about the arrival of the apocalypse.

The predictions conflict other end of the world forecasts, including that of serial end of the world predictor David Meade – who said April 23 would mark the apocalypse.

He said a mythological planetary system known as Planet X or Nibiru would appear in the sky on that date.

He claimed it would then pass the Earth in October, causing the start of the Rapture with huge volcanoes and volcanic eruptions due to its gravitational force.

And not everyone is convinced with this latest theory.

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Last year, Meade also said the end was imminent. But the dates came and went.

“These [predictions] are not consistent with the biblical stories,” argued author Jonathan Sarfati of Creation Ministries International, referring to Meade.

“Everything Meade said about April 23 he said last year.

“At some point we have to stop believing people who keep crying ‘wolf.’

“I wish people would stop saying these things and stop scaring people.”

Sarfati says that such doomsday predictions reflect little understanding of astronomy and theology.

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He said that the movement of the planets, which Meade cited, occurs every few years — and the Earth continues to exist.

That’s not to debunk the belief and biblical teachings about an end and Judgment Day, experts say.

While people of different faiths believe that there will be some religious end to life on Earth, they disagree about how it will happen.

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Scientists have several theories about when Earth will be destroyed, although none of the data points to this Monday.

The most widely accepted theory is that the Sun, which is already gradually increasing in temperature, will expand and swallow up the planet. Some scientists believe this could happen as soon as 7.6billion years’ time.