2.a Making Eratosthenes’ measurement

Performing the experiment described in 2. Eratosthenes’ measurement.

The equinox here in Sydney occurred on 21 March, with local noon at 13:02 local time. Unfortunately the day dawned grey and rainy, with bands of heavy rain blowing in from the south.

As midday drew closer the rain eased off tantalisingly, and there was even a glimpse of blue sky, only to be followed by more heavy rain. Undaunted, a friend joined me for an expedition to a suitable location to make the measurement. I took with me my handy wizard staff to serve as the vertical stick, and a spirit level and tape measure.

We found some flat ground near the McMahons Point ferry wharf, and waited for a break in the clouds. My friend suggested that if we encountered any police and they asked why we were carrying around a quarterstaff, we should say, “Ohhh, just doing a little weather experiment”.

Waiting for the clouds to clear

Waiting for the clouds to clear.

Magically, about 15 minutes before solar noon, the clouds parted and a hot sun shone down out of the sky. We took some quick measurements in case the patchy clouds obscured the sun at the critical time, and they drifted across the sun, turning it on and off as we waited.

Fortunately, around 13:02, there was a good few minutes of uninterrupted sunshine and we measured the shadow of the staff carefully a few times, making sure the staff was held vertical with the spirit level.

Sunshine at local solar noon

Sunshine at local solar noon. Boldly doing Science!

Science successfully done, we headed to a nearby Japanese restaurant for a well-earned lunch!

I’ve been receiving measurements from all across the world today, and have run some preliminary numbers to get results. They look pretty good! But I’ll wait until everyone’s measurements are in before presenting a full report.

5 thoughts on “2.a Making Eratosthenes’ measurement”

  1. I’m sorry to say we had a fair bit of hazy cloud today so I didn’t get a measurement – I’d been eyeing off a nice sharp corner on a garden wall (to serve as a pre-planted stick) in the rooftop basketball court opposite work all week but today wasn’t the day I wanted. Nonetheless I’m pleased to hear that other measurements are rolling in and you had enough sun to get your own!

  2. I tried to do it. I even brought a 5 foot (approximately) length of PVC pipe to work to measure.
    I live in Las Vegas, which has on average, 350 sunny days a year. Yesterday was so overcast that there were no visible shadows at all. Had the same weather last year when there was that spectacular full solar eclipse that everyone was so excited about. 🙁

  3. Heavy…
    Would be interesting to see a rough breakdown of all the data points by country/city

    1. Yes, I’ll be supplying detailed stats on the measurements after I’m sure they’ve all been sent to me.

  4. I had to go to a meeting at work during the local solar noon, and it was not quite as much fun as measuring the shadow of a stick.

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