Perhaps when you first dressed up as a ghost and went round the houses asking for sweets you thought to also ask what was the meaning of Halloween and why are we doing this? In case, like me, you didn't, I can share for you that Halloween is a smush together — or portmanteau — of hallow, of old English origin meaning Saint, and e'en, a contraction of the Scots word even meaning eve. So it's really the night before All Hallows or All Saints' day on the 1st of November when Christians celebrated the lives of past Saints and martyrs. It's also part of the season of events called Allhallowtide including All Souls' day on the 2nd of November and sometimes days beyond.

The other Halloween traditions come from a mix of sources over hundreds of years that are both complex and somewhat disputed. I did like that the Jack O'lantern, before transferring itself to a pumpkin in the US, was originally carved out of turnips. And I also read that a mighty one quarter of candy sold in the US is sold for Halloween.

Some of the better, sources, explaining the origins of Halloween.

Halloween

It might seem straightforward to pull out a map and measure the distance between two distant points, however, the larger the distance the bigger the distortion caused by traveling on the curved surface of the Earth as opposed to flat 2D space. So while the distance you measure to your neighbouring town won't be too bad, if you're measuring between London and Rio the curvature of the Earth will make a big difference to the distance that you'll travel. To help figure out the correct distance there's the haversine formula.

The haversine formula allows you to calculate the shortest distance between two points on a sphere using their latitudes and longitudes — this will be the arc between them on the great circle that includes both points. A great circle is a circle on a sphere with the same centre as the sphere, like the Equator. The haversine formula isn't perfect in practice, as Earth isn't a perfect sphere — see the 3 tallest mountains.

It was invented around two hundred years ago, together with tables to speed any calculations, to help sailors navigate.

The haversine formula

An average car, sat idling, can produce exhaust emissions to fill 150 balloons. That's a lot of balloons to imagine puffing away out of the cars idling outside a school for a pickup, say. Other tests have found (pdf) that for any time over 10s fuel use and emissions are always greater when idling than turning off the engine and restarting. Spread the word.

Of course, if you have an electric car this won't apply.

I did draw 150 balloons, but a few of them didn't fit on the page.

Idling