|Blood moon, Jerusalem 2008|
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…