In the feed of one online cult, its leader declared himself a messiah, conceived and born “in the only tetrad perfectly aligned with the cycle of Jewish holidays,” and named the date: October 18, 1967, blood moon, Sukkot. There is one word worth checking in that claim — tetrad. The rest belongs to a realm where astronomy is powerless.
A tetrad is four total lunar eclipses in a row, two in one year and two in the next, with no partial eclipses in between. The word sounds like astrology, but it means dry arithmetic: a lunar eclipse is possible only at full moon, full moons run on a schedule, and that schedule is known in advance — five thousand years ahead, down to the minute. That was the hook. A prophecy about a sign in the sky rests on a table compiled not by preachers but by two astronomers, and it is publicly available.
That leaves three questions. How many tetrads there really are. Why they land on Passover and Sukkot at all. And what the people looking at the Moon for scientific reasons were doing at the time.
The plane of the Moon’s orbit is tilted about five degrees to the plane of Earth’s orbit, so eclipses do not fall on every full moon: the windows open twice a year, in seasons. A total eclipse is when the Moon passes entirely into Earth’s shadow. Four totals in a row, without a single partial between them, are already rare — but a calculable kind of rare: the interval within a series is about 177 days, or six lunar months.
The scale is set by NASA’s catalog, which covers the period from 2000 BCE to 3000 CE. Over those five thousand years, Earth will see 12,064 lunar eclipses, 3,479 of them total — 28.8%. Any given year has between two and five eclipses, most often exactly two. Tetrads arrive in clusters, with long gaps: three hundred years may pass without a single one, then another three hundred will accumulate a dozen and a half. The cycle of these clusters — the tetrad cycle — stretches across roughly 586 years.
When NASA told readers about the beginning series in March 2014, the agency did not play it up: it states outright that this was the second of eight tetrads in the 21st century, while eclipse specialist Fred Espenak added that in the current lunar-eclipse cycle, tetrads are “a fairly common occurrence.”
Espenak and Jean Meeus also completed the Five Millennium Canon of Lunar Eclipses — a reference work listing, for every century, the number of eclipses of each type and, in a separate column, the number of tetrads falling within that century. The column looks like this: 1401–1500 — four, 1501–1600 — six, 1601–1700 — zero, 1701–1800 — zero, 1801–1900 — zero, 1901–2000 — five, 2001–2100 — eight, 2101–2200 — four, 2201–2300 — zero.
Hence the famous line about the lull: according to Espenak, there were no tetrads at all between 1600 and 1900. Howard Cohen, a Florida astronomy professor, measures the same pause slightly differently in an article on a “Jewish festival of eclipses” — from 1582 to 1908 — and adds that there will be sixteen between 1909 and 2156. Popular retellings shift the boundaries even further: a 2015 analysis in The Conversation says there were “no tetrads between 1400 and 1900.” The table does not bear that out — there were four in the 15th century and six in the 16th. Even careful authors differ over the numbers here: some, it seems, count only up to the present day, others go to the end of the catalog, where future tetrads are already mapped out.
The totals differ too: “fifty-seven tetrads since the first year of the Common Era” versus “sixty-two.” Most likely, the difference is whether to include those that have not happened yet. That is exactly the detail that makes any talk of a series’ “uniqueness” impossible to verify: it is unclear what you are comparing it to.
Elsewhere, though, the catalog leaves no room for interpretation. NASA’s page on the eclipses of 2025 gives a minute-by-minute schedule: on March 14, the total phase lasts from 06:26 to 07:31 GMT, magnitude 1.1784; on September 7, the maximum comes at 18:12:58. All of it was calculated long before it became news.
The Jewish calendar is lunisolar, and both key holidays begin on the fifteenth day of their month — that is, always at full moon. A lunar eclipse is likewise possible only at full moon. The overlap of those two conditions produces the effect preachers call a sign: according to figures cited by EarthSky, roughly one sixth of all eclipses fall on Passover or Sukkot.
Since the first year of the Common Era, eight tetrads have coincided with both holidays; between 1949 and 2051 there are eight tetrads, and in each one the spring eclipses fall on Passover, with those following them falling on Sukkot. But not every tetrad lands on the holidays. Of the eight series in the 21st century, only 2014–15 coincided fully with both; in the 2032–33 tetrad, only two of the four eclipses will fall on holidays, while the century’s other series have no such coincidences at all.
People noticed this calendar overlap before, without any eschatology. Cohen describes the evening of April 3, 1996, in Gainesville, Florida: Rabbi Allan Lehman interrupted the Passover dinner, and the guests went out into the field behind the synagogue — to watch the full moon rise above the trees. Instead of the familiar bright disk, a dim crimson sphere hung over the horizon: the full moon had fallen in the middle of a total eclipse. Dinner resumed.
The modern version of this story begins with two American preachers. Mark Biltz published Blood Moons: Decoding the Imminent Heavenly Signs, while John Hagee, founder of Cornerstone Church in San Antonio, published Four Blood Moons: Something Is About to Change — and it was his version that made the most noise. The book spent more than 150 days in Amazon’s top 150; by mid-April 2014, it stood fourth on The New York Times bestseller list in the advice category. Hagee explained to his flock: “The heavens are God’s billboard, and when something big is about to happen, He gives the Earth a sign.” In the same speech, he cited NASA as an ally: the agency, he said, confirmed that the event was coming.
Hagee’s scheme rests on three historical points: tetrads supposedly accompanied the expulsion of Jews from Spain, the creation of the State of Israel, and the Six-Day War. The arithmetic, though, is a mess. The expulsion took place in 1492, while the tetrad began in 1493; Israel came into being in 1948, while the tetrad began in 1949. A year this way, a year that way — in a sermon, it sounds like “those very years.” The tetrads beginning in 162, 795, 842, and 860 go unmentioned in the scheme altogether, as does the fact that there was no tetrad around the Holocaust.
The criticism did not come only from astronomers. Two Baptist professors took apart Hagee’s scriptural references: apocalyptic literature, they said, uses cosmic imagery as a figure of speech, while the apostle Peter in Acts applied Joel’s prophecy of the “moon into blood” to the Pentecost that had already happened, not to some deferred future.
Astronomers added their own point: three of the four eclipses in that series were not visible from Israel at all, and only the very end of the last one was. The panic, meanwhile, was real: people in Utah were buying up supplies, and before September 2015 a rumor spread online about an asteroid impact, which NASA’s Near-Earth Object office chief Paul Chodas had to debunk. The Geological Society of London separately explained that earthquakes have no connection to the Moon’s phases, while the tide from a “supermoon” is at most ten centimeters higher than usual.
It is worth returning to the date in the cult post, because it can be checked. Sukkot 5728 began on Wednesday, October 18, 1967 — the calendar confirms it. And there really was a total lunar eclipse that day: magnitude 1.1426 (a magnitude of one would mean that the Moon had entered the shadow by exactly its own diameter; here it went deeper), the total phase lasted 59 minutes 45 seconds, and maximum came at 10:15 GMT. It was the second eclipse in the 1967–68 tetrad, between the eclipses of April 24, 1967, and April 13, 1968.
One more thing lined up: the Six-Day War was fought in June 1967 — precisely in the interval between the first and second eclipses of that series. The same tetrad preachers have spent half a century using as proof also became the birth date of yet another messiah.
There is one difference. The eclipse of October 18, 1967, was visible over northeastern Asia, western North America, and the Pacific Ocean. In Jerusalem it was noon: the Moon was below the horizon, in Earth’s shadow, and astronomically speaking, there was no way to see its “sign” from there. Whoever named that date simply read the table — the very one where everything is laid out in advance.
Nothing. The tetrad ended on September 28, 2015, with its final eclipse — also the series’ only “blood supermoon”; the previous such coincidence was in 1982, and the next will come in 2033. The world did not change, but the word outlived the prophecy: in 2025, it appeared without fuss in headlines about the September 7–8 eclipse, whose total phase lasted 82 minutes and which some six billion people in the Eastern Hemisphere could see.
That was when it also became clear that the “sign” was not a sign at all. How red the Moon turns depends on how much dust and volcanic aerosol is in the atmosphere: in 2025, the air was relatively clean, and astronomers expected a bright orange-red disk. The sky works in two modes here: it gives you a schedule, and it serves as an instrument. It is just that the second mode scares no one.
On October 8, 2014, while Hagee was working his way through the print run, the LRO spacecraft orbiting the Moon was running observations with its Diviner instrument. It used the eclipse as an experiment: deprived of incoming heat, the Moon begins cooling rapidly, and from the rate of cooling it is possible to calculate the thermal inertia of the regolith’s uppermost layer. The geometry happened to line up neatly that time — the spacecraft’s orbit lay about thirty degrees from the subsolar point, and before the eclipse began the surface had been heated almost uniformly: around Kepler crater, to about 380 kelvins. The observations were taken in seven thermal-infrared channels, in a strip six kilometers wide and at a resolution of roughly 250 meters.
So a total lunar eclipse is an instrument too. The Moon cools in shadow on schedule, and its rate of cooling reveals what covers its upper layer.
The next tetrad is in 2032–33, and its schedule is already sitting in the public catalog, accurate to the minute. Someone will write about a sign again. You can do something else: in April 1996, a rabbi in Gainesville pulled his guests away from their Passover dinner, led them outside, and showed them what a full moon looks like when it falls into Earth’s shadow. Nothing happened.