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I can never spell Eratosthenes right on the first go. Yes, I have done so enough times that it's an actual repeat phenomenon.

Hey, want to do some mass science? David Morgan-Mar (PhD, LEGO®©™etc)’s new sci-comm projects (cf: yesterday) is looking to see if we, in the modern age, can figure the size of the Earth and distance to the sun using the same methodology as Eratosthenes (that is to say, a stick, a piece of string, and math), but perhaps with more accuracy:

[prep steps omitted]
On the equinox date, at the exact time of your local solar noon: If it’s sunny, place your stick vertically on your flat area. Do this as accurately as you can — use a spirit level or inclinometer if you can. If you don’t have one, let the stick dangle from the top, with the bottom just barely touching the ground. With the stick vertical, measure the length of its shadow cast by the sun, again as accurately as you can manage. Using a friend to help you will make things easier.

Once you have the shadow length, you’re ready to report your data! I need to know: (1) Where you were — city, state, country — enough that I don’t get it wrong. (2) The length of your vertical stick. (3) The length of the shadow you measured. Send these three bits of data to me by email [dmm at], by the end of March.

As luck would have it, I already have a stick from a couple of years ago when Radiolab crowdsourced ground temperature data¹ to predict when the 17 year cicadas would come up. I also live in a somewhat perplexing microclimate where massive meteorological events will suddenly split in half, go around town, then rejoin on the far side.

The other part of this situation is that everything in the sky that is interesting — lunar eclipses, solar eclipses, astronomical conjunctions and convergences — invariably happens behind a thick bank of clouds. But I’ll give it a try as best I can, and I invite you to do the same. Five minutes of looking stuff up on the internet, two minutes of holding a stick and making a measurement, one minute to send an email. It’s for science.

Spam of the day:

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You want to pay me to put up with the sort of visitors who would sell their clicks? Sure, I’ll accept them for a half-hundo.

¹ A stick with a temperature sensor, attached to an Arduino and a string of LEDs, no less. For Morgan-Mar’s deal, you just need a stick.

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