Solar eclipse 2017

A solar eclipse occurs when the moon passes between the earth and the sun. A total eclipse occurs when the moon fully blocks the sun; these are quite rare as they only exist along a narrow path on the surface of the Earth. Other types of eclipses are annular and partial when only part of the sun is obscured.

Solar eclipse [2017] 03

On 21 August 2017 the US will experience a total eclipse. This is a big event as the last total eclipse observable in the continental US was in 1979 (when, in fact, the weather was not the best). And the last solar eclipse whose path of totality moved from coast to coast (as it will in 2017) was back in 1918. Of course, this being the United States, the Americans will no doubt play the whole thing down and it may pass many by without being noticed at all.

It can be a scary thing when the sun suddenly disappears in the middle of the day and in olden times people would become fearful at the time of eclipses. Various stories were told to explain the terrible event. Many of these myths involved the sun being eaten by a large animal, for example in Vietnam people believed that a giant frog was devouring the sun (has this actually ever been truly disproved?) Customs developed to chase away whatever was eating the sun by banging pots and pans ­ so far this has proved a remarkably successful strategy and has worked every time.

Scientists (slayers of myths, and general killjoys) claim that there is no evidence that solar eclipses affect human behaviour, health or the environment.

But is this true?

The above table lists all the total solar eclipses seen in the US since 1900, with in each case a sparkline showing the Dow Jones Industrial Average for the four days around the eclipse (the eclipse is on the 3rd day).

And the following two charts plot the returns of the Dow Jones Industrial Average on the days around the 15 total solar eclipses that have been visible from the United States since 1900. S(-1) is the day before the eclipse, S(0) the day of the eclipse, and S(+1) the day after. The following chart plots the average return for the three days…

Solar eclipse [2017] 01…and the chart below plots the proportion of days that had positive returns.

Solar eclipse [2017] 02

It can be observed in both the sparklines and the bar charts that on the day before the eclipse, and on the day itself, the market tends to be weak (investors fearful of the big frog). But on the day after the eclipse the market bounces back ­ the frog has gone and the sun is back.

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