Blood Moon Rising

Blood moon, Jerusalem 2008
There’s going to be a blood moon this Passover. I’m not really a numbers junkie – contrary to popular belief and I’m amused therefore by the flood of conspiracy theorists, amateur prophets and other assorted apocalyptically inclined savants who claim to attach meaning to so-called “blood moons”, in particular in groups of four, occurring on four High Holy Days or Jewish festivals.  These sporadic yet predictable sets of four closely timed eclipses, called tetrads, depend on a precise alignment of the sun, Earth, and moon. (To visualise an eclipse, imagine you’re standing on the moon watching the earth pass in front of the sun). In case people haven’t been paying attention, this Passover coincides with  the third of four of these “blood moons” – which NASA labels as the phenomenon of four full lunar eclipses in two years. The first was on Passover last year, the second on Succot last year and the final one is on Succot this September.

This particular tetrad is unusual, as all four of its eclipses are total, this one, unfortunately, only visible early Saturday morning from central Australia across the Pacific region perhaps as far as Hawaii.  During more common partial or penumbral eclipses, only the earlier, less-cool stages of the eclipse occur — there is no total blockage of the moon, and no eerie red glow, caused by Rayleigh or inelastic scattering which we can explain as follows. As white light passes through the atmosphere, shorter or bluish wavelengths are scattered from excited nitrogen and oxygen molecules and are lost in space. Longer wavelengths are more likely to make it through without being scattered and arrive at the moon. Since red light has the longest wavelength, so the moon ends up looking red – the same reason sunrises and sunsets look red – the more white light is filtered through our atmosphere, the redder it gets. When the sun, Earth, and moon are aligned perfectly, not all of the sun’s light will be completely blocked out by Earth, some will pass through Earth’s atmosphere and then hit the moon.

Of the eight blood moon tetrads since the time of Christ, Israel’s War of Independence and the Six Day War both occurred during these periods, which is why some people are casting around for meaning, particularly in light of the Jewish belief that blood moons are ‘a sign to Israel’.  The Internet is littered with candidates, so if you’re interested all kinds of possible historical attributions can be found, including juxtapositions of the ‘sign to the nations’ of a solar eclipse somewhere in the cycle.

Much as it may seem otherwise, I’m neither a scoffer nor a convert to any particular theory, so,  in conclusion, I’ll leave you with this. “And God said ‘let there be lights in the heaven’s firmament, to separate between day and night, and they will be for signs, and for festivals, and for days, and years.’”  (Genesis 1:14)

As it happens, the 21st century as a whole will see eight tetrads – an unusually high number, so perhaps the best plan is just to wait and see…

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