New Mexicans for Science and Reason


Simple, Inexpensive Experiment Proves Earth is Round!

by Dave Thomas

Online Horizon Calculator

New! Viewing Sandia Peak from atop M Mountain

Flat Earthers like to say that "Water finds its own level." For a few dollars, anyone can get some equipment that Proves the earth is round. You'll have to take it up to the mountains for best effect.

Theory: Use a Spirit Level as shown, to find True Level.

Here's how the above would look like to a viewer on the Flat Earth:

But, here's how the above would look like to a viewer on the Round Earth:

You'll want Maths! Here they are. R is the radius of the Earth (3960 miles), h is the altitude of the viewpoint (also in miles), and d is the distance to the effective horizon on a Round Planet. θ is the angle between True Level (straight ahead) and the Horizon (the visible edge of the Earth). Saying that the Horizon is Level is the same as saying θ = 0. But, θ is NOT Zero!! And the Horizon is below True Level.

Here's this experiment actually works out at Sea Level. Sea Level is just a hair below True Level.

Here's this experiment actually works out in the Mountains. At an altitude of almost two miles above sea level, the horizon is OVER a DEGREE below True Level.

New! Viewing Sandia Peak from atop M Mountain
On February 25th, 2018, four individuals drove to the top of M Mountain (Socorro, New Mexico), and measured the apparent elevation of Sandia Peak, some 84 miles to the North. Since Sandia Crest is over a half mile higher than M Mountain, if the earth was flat, one would have to look upwards to see the Sandias from Socorro. These measurements showed that Sandia Crest, as seen from atop M Mountain, appeared below True Level, which is only possible on a Round Earth.

M Mountain (a.k.a. Socorro Peak), just west of Socorro, NM. From on top of this peak, you can see Sandia Crest, some 84 miles to the north. M Mountain's peak is at 34.07N, 106.958W, elevation 7,200 feet.

The Sandia Mountains, east of Albuquerque, NM. This splendid photo is courtesy Frank Etscorn. Sandia Crest is located at 35.21N, 106.45W, elevation 10,600 feet.

Top: Our view of the Sandias, from atop M Mountain. Photo courtesy Matt Thomas. Bottom: view of the Sandias from Belen, some 40 miles north of Socorro. Photo by Dave Thomas.

This panorama by Matt Thomas shows the Sandias off to the North (1/3rd of way from left), and spirit level and theodolite experiments underway.

A side view of a simple Spirit Level. It's a tube, with some colored water inside. Since Water finds its own LevelTM, you can measure the angle of True Level by sighting along the tops of the two water columns.

The Spirit Level in action.

Here, the image above has been annotated to show True Level.

Here, the Sandias have been outlined. Since the Sandias appear below True Level, we are looking down on them. But, the Sandias are 10,600 feet in elevation, two thirds of a mile higher than M Mountain, at 7,200 feet elevation. If the Earth were Flat, you would be looking UP from M Mountain to Sandia Crest, 3,400 feet above.

Stephen T. Senn brought a theodolite! We found Level with this instrument, and then observed that Sandia Crest was below True Level as viewed from atop M Mountain, somewhat between 0.15 and 0.35 degrees.

Finally, I used a simple altimeter to measure the dip of the Sandias. Here, I am looking directly at Sandia Crest, and the device shows I am looking Downward by a good-sized fraction of a degree, confirming the other two results.

The expedition crew. Dave Thomas, T Reese Janca, Matt Thomas, and Stephen T. Senn. Sponsored by The Round Earth Society.

New Online Calculator!! Enter the number of feet in the cell, then tab or click outside to see the dip angle and distance!

English           Metric

Height above surface h = feet
Radius of the planet R = 3960 miles

Height above surface, h = miles

Dip Angle, θ = degrees

Distance to Horizon d = miles

Distance to Horizon d = km


Height above surface h = meters
Radius of the planet R = 6371 km

Height above surface, h = km

Dip Angle, θ = degrees

Distance to Horizon d = km

Distance to Horizon d = miles

Kudos to madmelon101. This photo was my original inspiration.

Think this is CGI? Get a plastic tube, go to the mountains, and see for yourself!

Flat Earth: 0           Globe: 4

As you can see, up in the mountains, the visible horizon is below True Level. Send in your pics, I will post them here!

Last Update: March 4th, 2018

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