TUNGSTEN VALLEY — Want to measure the entire Universe? You do it on six rungs of a distance ladder, starting with measuring the earth and then working upward and outward. We’ll climb those rungs together, one-by-one, for the next few months.

The journey of 13.8 billion light years begins with a single step. Or rather, a single turn of a wagon wheel.

About 2,200 years ago, Greek-Egyptian scientist-astronomer Eratosthenes combined a known north-south distance between two places on the earth with a pair of sun-angle measurements to compute the earth’s circumference to within a few percent.

The approach? Simplicity itself: Differing sun-angles between two north-to-south locales tells you the fraction of a circle they subtend. If you get the mileage of that fraction, then the mileage for the entire earth falls right out.

Eratosthenes knew that on a given day the sun was directly overhead at one place, Cyene, shining straight down a deep well. At another place, Alexandria, that same day it was 7.5 degrees off vertical. The north-south mileage between the two came from an odometer-equipped cart. (Roman engineer Vitruvius describes the ancient device, geared to a calibrated wagon wheel.)

Some commenters get hung up on the absolute accuracy of Eratosthenes’ answer, debating the exact size of the unit he used, the stadia. This completely misses the point that his method inherently gives a highly accurate answer; the length of his particular stadia is beside the point.

Re-creating Eratosthenes’ experiment would make an excellent high-school level student project. The idea is that the students work with their hands and their brains to plan the work, build the gear, take the data, analyze the results, and write their conclusions. Working in multiple teams, they prep and plan locally with adult guidance and supervision. 

Then, chaperoned, some of them go to Liberal, Kansas, while others drive (are driven) from there to Bismarck, North Dakota. They use odometers to measure their northward run. Established in the two places, the independent teams (perhaps two in Liberal and two in Bismarck) make simultaneous (down to the minute!) observations of the sun’s elevation with calibrated sticks.

They cannot use: clocks, watches, glass optics, smart phones, computers, or any AI. Only vertical sticks and odometers are allowed. The road-trip part can be done over a holiday weekend in the school year, or else a few days in the summer.

What do the students gain? They learn to think and work through a complex problem, and a scientific challenge, from beginning to end. They learn to overcome the challenges of designing, building, and using measurement gear to obtain precise data. And they learn that the job’s not done until they’ve written up (published) their results.

This correspondent doesn’t know whether this kind of project comports with the current mania for rote teaching for tests; taking tests; and then prepping for the next round of tests. Instead, this project teaches creative thinking and doing. Is there room for that anymore?

In September skies:

The sun begins the month in Leo (and then Crater), entering Virgo on September 16. On the fall equinox (4:47 p.m. in Nederland on September 22), days equal nights at 12 hours each.

The moon’s dates are: Last Quarter September 4; New September 10; First Quarter September 18; Full (Harvest or Corn Moon) September 26.

September Meteors: The epsilon-Perseid shower (parent of an unknown retrograde comet with ~ 1,000 year period) peaks on September 9.

Best Sky Viewing Nights (Minimal Moon): September 1-17.

Sunset (Mid-Month): Deneb is nearly overhead in the east; Vega is overhead; Altair is in the south-southeast. Hercules with its striking M-13 globular cluster is overhead. Sparkling Sagittarius, with our nebula-rich galactic center, is low in the south.

Midnight (Mid-Month): Auriga (the Charioteer) with brilliant-white Capella is in the northeast. Perseus is high in the east. Pegasus is nearly overhead while Altair sets in the west.

Sunrise (Mid-Month): Orion is due south. Procyon (Star Before the Dog) is high in the southeast. Cetus (the Whale) is low in the southwest.

Mercury, moving from Leo to Virgo, is very low in the west at sunset.

Venus, Virgo and then Libra, is the Evening Star, very low in the west at sunset.

Mars, in Gemini next to Castor and Pollux, rises at 1:40 a.m. and is high in the east at sunrise.

Jupiter, in Cancer, rises at 3:40 a.m. and is low in the east at dawn.

Saturn, in Pisces, rises at 8 p.m., is high in the south at 2 a.m. and is low in the SSW at sunrise.

New power diet for Voyagers: As Voyagers 1 and 2 probe interstellar space, their plutonium power sources are sputtering at half their original output. To prolong the probes’ lives, mission engineers are uploading a “Big Bang” program that deactivates some systems and starts lower-power alternatives for others. This new power diet should extend the probes’ lives by another year. 

Frank Sanders, a spectrum scientist, takes astronomy-related inquiries at backyardastronomy1@gmail.com.