Exposing PseudoAstronomy

April 14, 2014

As We Approach the Era of the Blood Moon Tetrad, Here’s What You Need to Know


Coming out of the 2012 (Mayan apocalypse) non-event, many of us wondered what the next doomsday would be. At the time, I said in several interviews that I didn’t know. This “blood moons” thing, however, seems to have grasped the attention of many, and since it has another 18 months to play out, I anticipate it might grow considerably. I hope not, because it’s silly, but we’ll see.

For those just coming here from an internet search, and you haven’t followed this blog at all, a few months ago I put out a podcast episode that thoroughly addressed this issue. I suggest it as a starting point.

The purpose of this blog post is to briefly summarize those issues again, and to go over a few small things that I did not address in that episode. And to say, once again, there is absolutely nothing to worry about, the whole thing smacks of people for thousands of years fearing comets or eclipses because they didn’t understand them. This time, we understand them, but some people still irrationally fear them.

Edited to Add: Conspiracy Skeptic Karl Mamer interviewed me and got the interview up really fast. It’s an hour:15 about these issues.


Tetrad: Lunar eclipses can be penumbral (it just dims a bit), partial (only part of the moon is in total shadow), or total (full moon is in Earth’s shadow). They can happen in any order or combination, but when four lunar eclipses in a row are total, that’s called a “tetrad.”

Blood Moon: A spooky/scary -sounding name for a total lunar eclipse because the only light that can reach the moon is filtered through Earth’s atmosphere, leaving only long wavelengths of light, the red light. So, the moon appears dark and red. Yeah, scary.

Lunar Eclipses

Very briefly, the moon orbits Earth, and the plane of its orbit is tilted about 5.1° relative to Earth’s path around the sun. So, it crosses that path twice in its orbit (called nodes). Only on those points could an eclipse possibly occur. And, only when those points happen during a new or full moon do you actually get an eclipse.

When it happens during a new moon, that’s a solar eclipse. Full moon, it’s a lunar eclipse. If a part of the moon would see the sun partially eclipsed by Earth, that’s a penumbral eclipse and you just get a small dimming. If a part of the moon would see the sun totally eclipsed by Earth, then that part is totally eclipsed, called an umbral eclipse. When the whole moon is in an umbral eclipse, it’s a total eclipse.

Eclipse Seasons

Because of the way the moon’s orbit works and the nodes line up, if you have an eclipse, you will likely have the other kind (solar or lunar) 2 weeks earlier or later. And, then they go out of alignment. Six months later, they’re back in alignment, and so you’ll usually get another 2 or 3 eclipses, 2 weeks apart.

And, the whole thing repeats something like every 18.6 years.

Jewish Calendar and Holidays

The Jewish calendar is a lunar calendar, meaning that new moons start a new month and full moons are in the middle of the month.

Most Jewish holidays are tied to the Jewish calendar and happen on either the first of the month or on the middle day of the month.

Therefore, by definition, most Jewish holidays will happen during either a new moon or a full moon. Therefore, by definition, the likelihood of a lunar or solar eclipse happening exactly on a Jewish holiday is much, much higher than for holidays based on a solar calendar.

Aside: Who’s Behind the Phenomenon?

That would be Pastor Mark Biltz. He originated this back around 2008, and it got very little attention. That’s changed.

Biltz’s story is that he went to NASA’s website and saw that there were these eclipses and tetrads, he saw that some of the tetrads happened during Jewish holidays, in his mind he thought that some of those resulted in doom (more on that later).

When he relates the story, he makes a big deal about how the data all comes from NASA in an apparent argument from authority. While it’s true that you can get a whole bunch of eclipse data from NASA, Pastor Biltz apparently has some issues reading big bold text. For example, he claims that NASA posts eclipse data for the “past 5000 years.” Except, it’s for the past 4000 and next 1000.

It’s a minor issue, but it calls into question how good he is at reading even less obvious signs which is the entire basis for his claims. (And Pastor Biltz claimed that Christopher Columbus was Jewish – he insisted on it – despite the fact he was a Roman Catholic. Again, signs of poor scholarship and a willingness to warp something to fit his ideas.)

More to This Phenomena: How Often Do Lunar Eclipses Occur?

Pastor Biltz claims that NASA data shows that 3479 total lunar eclipses have happened in the past 5000 years. It’s actually past 4000 and next 1000, but, whatever. He says that this means you only get an average of 1 total lunar eclipse every 1.5 years (it’s 1.4, but moving on), but OMG we get 4 in the space of only 18 months this time!!!!

This sounds like it’s way over the average. Which it is. But, using an average is the wrong statistics for this on the short-term. Eclipse seasons and the way the orbits work out mean that you typically get these occurring in spurts. You get a lot of penumbral, then a few total. Or, 2-3 total, then 1 partial, 2 total, 5 penumbral. Before this April, we had 1 partial, 1 penumbral, 1 partial, and 2 penumbral. No total eclipses for 2.5 years!!!!

My point is that it’s fine to say that, on average, these happen once every 1.5 years over the long term. But, then going ahead and using that to say that a particular year, two years, or even decade is above or below “average” is an abuse of the statistics.

More to This Phenomena: How Often Do Tetrads Occur?

There’s no nice, simple formula predictor that gives you a way to figure this out. Happily, Universe Today has a nice table. It shows that during the 11th-13th, 17th-19th, 23rd-24th, and 28th-29th centuries, there are 0. 14th there were 6, 15th there were 4, 16th there were 6, and 20th there were 5. This century, we get a whopping 8, and next century we get 4.

So, they are not exceedingly rare, but, they’re not that common. This generation has or will see several. Our great-great-great-great grandparents saw none.

More to This Phenomena: How Often Do Tetradal (is that a word?) Eclipses Occur on (Major) Jewish Holidays?

Well, because tetrads are relatively rare, and they tend to precess through the months (because lunar eclipses precess through the months), it is somewhat more rare than tetrads. But again, by definition, it is likely that they will happen on Jewish holidays. Not necessarily major ones, but on Jewish holidays. This time, they just so happen to fall on major ones.

More to This Phenomena: What Happened Last Time?

So, the last time the tetrad happened during Passover, Sukkot, Passover, Sukkot, was April 24, 1967 – October 6, 1968. Pastor Biltz says the big thing that happened to Israel during that time was the 6-day war, which was June 5-10, 1967. So, during the “blood moon season,” but not during or even really near any eclipse (in fact, about as far as you could get – 3 months before and 3 months after the next/last one). And, based on an objective look at the history, Israel won. And Israel increased its land holdings significantly. I wouldn’t call that a “bad” thing for Israel.

What about before that? The previous tetrad also happened over two successive Passovers and Sukkots, and that was April 13, 1949 – September 26, 1950. What does Pastor Biltz point to as the major bad event concerning Israel that this Sign in the Heavens pointed to? Israel was founded. May 14, 1948. 11 months before the first eclipse in that tetrad.

Ummm … not a bad thing for Israel, and the fact that he has to search nearly a year to find something significant makes me, well, skeptical.

Retrodiction, Prediction, Cherry-Picking …

By this point, it should be very clear how I feel about this issue. But, let’s put it another way: You have a somewhat rare event, and you find something bad (or good) that happened during or within a year of that event, and say the two are related (correlation = causation fallacy). That is what Pastor Biltz has done. Nothing more, nothing less.

Why do I say this? Well, I took a simple internet search of “Timeline of Jewish History” and, nicely, Wikipedia has something on that. Yeah, some of you may not like Wikipedia, but regardless, you can still use it as a starting point. And, gasp!! pretty much every year, something important happens to Jews. Or, same thing with a timeline of Israeli history.

My point is that if your criteria is vague (“something” has/will happen) and you’re allowed to include events that happened practically within a year of the event that already lasts 18 months (so you have 42 months, or 3.5 years to find something), well, I’m unimpressed. Now, if something catastrophic that was a once-in-a-lifetime event happened exactly on the date that these tetrads started but only on the tetrads that coincided with the major Jewish holidays, then I might be more interested and look more closely.

But, let’s take a look at the last tetrad: May 4, 1985 – October 17, 1986. Biltz doesn’t say anything about that because the cycle happened +1 month from the Jewish holidays. Looking at those timelines of Jewish and Israeli history, the First Intifada started in 1987, just a year after the tetrad ended!

Or what about the importance of 1982, when Israel withdrew from the Sinai Peninsula? Or 1956, the war which brought Israel into the Sinai in the first place?

And Yet, There’s More!

Pastor Biltz has many other bits and pieces that feed into this. For example, that 2015 is a Shemittah year, every 7 years when Jews are supposed to let their fields lie fallow. Oh, and all debts, except foreign ones, are remitted.

Biltz claims that the last one (Sept. 13, 2007 – Sept 29, 2008) finished just as the Dow fell 7%! And the one before that (Sept. ?, 2000 – Sept. 17, 2001) the Dow fell 7.1%! Not being able to carry this much further, he pointed to the one in 1994 (Sept. ?, 1993 – Sept. 5, 1994) when, not on the last day of the Shemittah, but sorta in the middle, Comet Shoemaker-Levy 9 hit Jupiter with 21 fragments (it was actually many more than that, but hey, 21/3 = 7 so we get 7 again, so don’t let facts get in the way) in July 16-22, 1994.

Again, retrodiction.

Final(?) Thoughts

This is a really long post. And there’s a lot of stuff that Biltz and many others (such as John Hagee) have heaped onto this non-significant (but still neat!) astronomical event. I’ve tried in this post and the podcast to cover the major components and claims, and hopefully set some of you (who may have come here from an internet search for more information, or referred here by a friend) at ease.

Let me try to summarize more succinctly: The Jewish calendar is defined such that most holidays must happen during new or full moons, and lunar eclipses can only happen during full moons. Total lunar eclipses are called by fear-mongers “blood moons.” Yes, a tetrad is somewhat rare, and because elf the way things line up, it’s more rare that it will happen on the Jewish holidays, but not ridiculously rare because of the way the calendar is defined. But besides that, nothing bad happened the last two times. The time correlation that he and others have attempted to draw is flimsy and reeks of vague retrodiction to fit the story he/they want to tell. In fact, based on the events named, good stuff happened for the Jews and Israel.

So, I recommend that if you’re in a part of the world where you can enjoy this and the weather cooperates, go outside, take a look up, take your camera, and enjoy this not-everyday neat celestial event.


  1. I’m too far west to see the whole thing but I’ll certainly be looking up tonight, this will be my third or fourth lunar eclipse (They tend to blur together after time.)

    Still trying to work out how people can freak out over it though.

    Comment by Graham — April 14, 2014 @ 8:05 pm | Reply

    • [Non-PC answer, because I’m tired:] Lots of people are idiots. Oh, and true fact — at least 50% of people a=have below-average intelligence.

      Comment by Stuart Robbins — April 15, 2014 @ 4:55 pm | Reply

      • Turned out to be too far west to see the eclipse, when the moon rose it was full and bright (Perfect werewolf weather according to Robert E. Howard).

        Comment by Graham — April 15, 2014 @ 8:18 pm

  2. -menon

    Idiot means loner, the opposite of polit for feler. Insult mòrons, not idiots.

    Comment by alysdexia — April 25, 2014 @ 9:17 pm | Reply

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