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:

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The Cavendish


Photo: “RichTea”

The Cavendish Laboratory at Cambridge has had more than its fair share of major scientific discoveries. In this old building (which the Laboratory no longer occupies) worked James Clerk Maxwell, Lord Rayleigh, J. J. Thomson, Ernest Rutherford, Lawrence Bragg, James Watson, and Francis Crick, among others. Their discoveries included the electron, the neutron, and the structure of DNA. I’ve always wondered: did the genius ooze into the walls? Would I become a better scientist if I could sleep a night inside the old Cavendish building? Or would I see ghosts performing experiments?

The Cavendish opened on 16th June 1874, receiving a write-up in the (then new) journal Nature (10: 139–142, 25 June). A description by William Garnett is also available here. The inscription “Magna opera Domini exquisita in omnes voluntates ejus” was placed over the doors. This is taken from Psalm 110:2 in the Clementine Vulgate (Psalm 111:2 in Protestant Bibles). The English version, “The works of the Lord are great, sought out of all them that have pleasure therein,” was placed over the doors of the Laboratory’s new building.

In 1882 the Cavendish accepted women on equal terms with men, although the University itself did not award degrees to women until 1948. Eleanor Sidgwick was the first woman to work at the Cavendish (1880–1882). Elsa Neumann joined in 1899, and Katharine Burr Blodgett in 1924.


Photo: William M. Connolley

The Bible

This classic visualisation by Chris Harrison shows 63,779 cross references within the Bible as coloured arcs. The bar chart at the bottom shows the number of verses in each chapter (the lengthy 119th Psalm stands out visibly).

Cross references are visible at several different scales. For example, a spray of yellow arcs terminating at the lower right marks the numerous Old-Testament references in the book of Hebrews. This diagram won an honourable mention in the 2008 International Science and Engineering Visualization Challenge.