140411163359-01-lunar-eclipse-0414-horizontal-galleryProphecy loves signs from the heavens, and they will deliver Tuesday with a moonlight spectacle.

What will happen could sound sort of like this:

The moon will turn to blood as it aligns with Earth and sun
Then do so thrice more ere a year and a half is done,
‘Tis not the herald of the apocalypses
Just the first of four total lunar eclipses.

In other words, get ready for an unusually beautiful moon to grace the night skies next week. There will be a total lunar eclipse Tuesday that will turn the moon a burnt reddish orange, NASA says.

It’s called a blood moon, and this one is just the first in a series of four consecutive total eclipses.

Within a year and a half, North America will be able to see a blood moon a total of four times. The moon takes on this color during the eclipse as it passes through the Earth’s shadow, which is the color of a desert sunset.

The four blood moons will occur in roughly six-month intervals on the following dates: April 15, 2014; October 8, 2014; April 4, 2015, and September 28, 2015.

With that frequency, one might be misled into thinking that they are commonplace.

There are about two lunar eclipses per year, NASA says. Some of them — penumbral eclipses — are so subtle, they are vaguely visible and go greatly unnoticed.

Other eclipses just cast a partial shadow on the moon but lend it none of that brilliant sunset hue.

Lunar eclipses — penumbral, partial or umbral — occur in random order, NASA says. Getting four umbral eclipses in a row is like drawing a rare lunar poker hand of four of a kind.

Just like the poker players, astronomers have a name for that lucky draw. It’s called a tetrad, NASA says.

“The most unique thing about the 2014-2015 tetrad is that all of them are visible for all or parts of the USA,” longtime NASA eclipse expert Fred Espenak said in a prepared statement.

In the 21st century, there will be many tetrads, but look back a few centuries, and you’ll find the opposite phenomenon, Espenak said.

Before the dawn of the 20th century, there was a 300-year period when there were none, he said. Zero.

That would mean that neither Sir Isaac Newton, Mozart, Queen Anne, George Washington, Napoleon, Abraham Lincoln nor their contemporaries ever had a chance to see one.

So, we’re in luck. To take advantage of it, you’ll have to stay up late from Monday night into Tuesday.

People in North and South America will be able to see the entire eclipse, while sky watchers in the western Pacific can catch only the last half. The moon will be setting in most of Europe and Africa during the eclipse, so residents there probably won’t see much.

For gazing geeks, NASA has set up a live web chat to answer questions about the eclipse starting at 1 a.m. Eastern Time.

The heavenly curtain rises on Tuesday’s lunar review around 2 a.m. ET, when the moon starts to slide into Earth’s shadow.

It should turn into a blood moon — a coppery red — about an hour later and stay that way for over an hour, NASA says.

Tuesday’s blood moon comes right on time for the Jewish festival of Passover, which commemorates the ancient Israelites’ exodus from slavery in Egypt. According to the Bible, God cast 10 plagues upon the Egyptians, the final plague being the death of the firstborn. The Israelites painted lamb’s blood on their doorways so that this plague would pass over their homes.

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What is a lunar tetrad? Both astronomers and followers of certain Christian pastors are talking about the lunar tetrad of 2014-2015. What is a tetrad? It’s four successive total lunar eclipses, with no partial lunar eclipses in between, each of which is separated from the other by six lunar months (six full moons)

Blood Moons in Biblical prophecy. We’re not experts on prophecy of any kind. But we’ll tell you what we know about the new definition for Blood Moon that has raised so many questions recently.

From what we’ve been able to gather, two Christian pastors, Mark Blitz and John Hagee, use the term Blood Moon to apply to the full moons of the upcoming tetrad – four successive total lunar eclipses, with no partial lunar eclipses in between, each of which is separated from the other by six lunar months (six full moons) – in 2014 and 2015. John Hagee appears to have popularized the term in his 2013 book Four Blood Moons: Something is About to Change.

Mark Blitz and John Hagee speak of a lunar tetrad as representing a fulfillment of Biblical prophecy. After all, the moon is supposed to turn blood red before the end times, isn’t it? As described in Joel 2:31 (Common English Bible):

The sun will be turned to darkness, and the moon to blood before the great and dreadful day of the LORD comes.

That description, by the way, describes both a total solar eclipse and total lunar eclipse. Sun turned to darkness = moon directly between the Earth and sun in a total solar eclipse. Moon turned to blood = Earth directly between the sun and moon, Earth’s shadow falling on the moon in a total lunar eclipse.

This book, published in 2013, is apparently what launched all the questions to our astronomy website about Blood Moons.  We confess.  We haven't read it.

Dates of Biblical prophecy Blood Moons in 2014 and 2015. These are the dates for the upcoming tetrad – four successive total lunar eclipses – in these years.

2014:
Total lunar eclipse: April 14-15
Total lunar eclipse: October 8

2015:
Total lunar eclipse: April 4
Total lunar eclipse: September 28

There are a total of 8 tetrads in the 21st century (2001 to 2100). But proponents of this Biblical prophecy regard the upcoming tetrad as especially significant because it coincides with two important Jewish holidays: Passover and Tabernacles.

The April 2014 and April 2015 total lunar eclipses align with the feast of Passover. The October 2014 and September 2015 total lunar eclipses align with the feast of Tabernacles.

The Jewish calendar is a lunar calendar. In any year, it’s inevitable that a full moon should fall on or near the feasts of Passover (15 Nissan) and Tabernacles (15 Tishri). Nissan and Tishri are the first and seventh months of the Jewish calendar, respectively.

It is somewhat ironic that three of these four lunar eclipses are not visible – even in part – from Israel. The only eclipse that can be seen at all from Israel is the tail end of the September 28, 2015 eclipse, which may be observable for a short while before sunrise.

How common is a tetrad of total lunar eclipses? Depending upon the century in which you live, a lunar tetrad (four consecutive total lunar eclipses, spaced at six lunar months apart from one another) may happen fairly frequently – or not at all.

For instance, in our 21st century (2001-2100), there are a total 8 tetrads, but in the 17th, 18th and 19th centuries, there were none at all. If we include all the centuries from the 1st century (AD 1-100) through the 21st century (2001-2100), inclusive, there are a total of 62 tetrads. The last one occurred in 2003-2004, and the next one after the 2014-2015 tetrad will happen in 2032-2033.

However, if we want to know which tetrads specifically fell on the Jewish feasts of Passover and Tabernacles, there appear to be a total of 8 in these 21 centuries:

1. 162-163 C.E. (Common Era)
2. 795-796 C.E.
3. 842-843 C.E.
4. 860-861 C.E.
5. 1493-1494 C.E.
6. 1949-1950 C.E.
7. 1967-1968 C.E.
8. 2014-2015 C.E.

Why is the term Blood Moon being used to mean a full moon of a lunar tetrad? We can’t really tell you why more and more people are using the term Blood Moon to describe the four full moons of a lunar tetrad. We don’t know why, exactly.

Here’s the definition of a lunar tetrad, again: four successive total lunar eclipses, with no partial eclipses in between, each of which is separated from the other by six lunar months (six full moons). There’s no obvious reason why Blood Moon should be associated with this term.

To the best of our knowledge, however, the use of the term Blood Moon to describe a lunar tetrad is of recent origin. It might have originated with John Hagee’s 2013 book.

We’re still not sure whether Blood Moon pertains to the full moon of any tetrad, or specifically to a tetrad that coincides with the feasts of Passover and Tabernacles.

Either way, I suspect the nouveau definition of Blood Moon will gain traction as we approach the tetrad, the four total lunar eclipses of 2014 and 2015.