Tuesday, August 14 , 2018, 4:27 am | Overcast 67º

 
 
 
 
Astronomy

Dennis Mammana: Flat Truth About a Spherical Earth Goes South

How far south can you see this week? Click to view larger
How far south can you see this week? (Creators.com illustration)

Believe it or not, there remain quite a few people who still believe we live on a flat Earth. How they’ve managed to escape exposure to the scientific advances of the past 2 millennia I’ll never know. Perhaps they think that these are all hoaxes perpetuated by “the guvment.” I wish I had an answer.

In any case, the idea of a spherical Earth is not at all new. The concept goes back to the sixth century B.C., when the Greeks began discussing the topic; and then, around 330 B.C., the wise philosopher Aristotle offered some observational evidence to support this round-Earth idea.

The matter was essentially resolved about a century later when the mathematician Eratosthenes noticed that on the summer solstice, shadow lengths were different in the Egyptian cities of Alexandria and Syene. From the length of these shadows he used geometry to not only show that the Earth was spherical but also calculate its circumference to within only a few percent of what we know today. Not too shabby for a guy in a toga and sandals!

We modern stargazers can use Aristotle’s technique to easily demonstrate the Earth’s curvature by simply looking skyward while traveling to different latitudes. In fact, a perfect group of stars to help us stands upright in the southern sky around 9 p.m. local time (9 p.m. in all time zones) this week. Its name is Orion.

Orion represents a great hunter, its vertical rectangle of bright stars marking his shoulders and knees, and its three equally bright stars in a straight line forming his belt. What’s nice about Orion is that it lies directly over the Earth’s equator and can be seen from everywhere on the planet.

This means that if we were to stand on the equator and look skyward, Orion would pass directly overhead; from the North Pole, these same stars would appear split by our southern horizon. And from viewpoints in between, Orion would appear at different heights above our southern horizon.

Right now, everyone in North America can see Orion during evening hours and trace its belt stars eastward toward the star Sirius — the brightest in all the nighttime sky. But another bright star lies south of Orion, and only those who live in or travel to more southerly latitudes can see it.

Named Canopus, this bright star is easily visible to stargazers near and south of the equator. But, if you live farther north than about 37 degrees latitude, you can never see Canopus in your sky.

At a latitude of 37 degrees, you’d need a perfectly clear view toward the south to get a glimpse of Canopus as it clears the southern horizon for only a few minutes during February evenings.

Farther south of 37 degrees, Canopus appears higher in the south and adds the nighttime’s second brightest star to an already sparkling February sky.

This demonstration is possible only because our Earth is not flat; if it were, we would see the same stars wherever on Earth we stood. But because our planet is spherical, traveling north and south changes the positions of familiar stars in our sky and brings a whole new set of stars into view.

Dennis Mammana is an astronomy writer, author, lecturer and photographer working from under the clear dark skies of the Anza-Borrego Desert in the San Diego County backcountry. Contact him at [email protected] and follow him on Twitter: @dennismammana. Click here to read previous columns. The opinions expressed are his own.

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