2019 in science so far

This year in science so far (click to zoom). Clockwise from top left:


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Four blood moons? Really?

In recent times, there has been a degree of interest – particularly within the USA – in so-called “blood moons” (as in the above book). Although this phrase is intended to recall Biblical texts such as Joel 3:21 (“The sun shall be turned to darkness, and the moon to blood, before the great and awesome day of the Lord comes”), it actually refers to ordinary lunar eclipses. Lunar eclipses are great to watch (see photo below), but are actually not particularly uncommon – see this list.

Much has been made of the “coincidence” of lunar eclipses occurring on major Jewish holidays. However, the geometry of lunar eclipses (see below) requires the moon to be on the opposite side of the earth from the sun, which means that lunar eclipses only occur on full moons. Furthermore, the Jewish calendar is a lunar one, so that several major holidays – such as Passover (15th of Nisan), Purim (in Jerusalem, 15th of Adar), and Sukkot (15th of Tishrei) – always occur on full moons. Lunar eclipses have therefore occurred on major Jewish holidays many times over the past two millennia.

Basically, the whole theory makes about as much sense as the panic of 2012. But, of course, that’s no reason not to watch the next lunar eclipse, on 8 October: