## Sunset on Mountains

During a sunset, mountain peaks lose sunlight later than areas around them. From a viewer observing a mountain, a shadow can appear ascending from the base to the peak. And conversely, during a sunrise, mountain peaks get sunlight before the areas around them and a shadow can appear descending from the peak to the base.

This phenomenon occurs because the Earth is a sphere. As the altitude increases, the hours of daylight become longer. It makes the sun rise earlier and set later.

## The Alignment of Mountain Peaks is Evidence that Earth is a Sphere

From the top of a mountain, we can easily see the other peaks afar. And from the visibility and the orientation of the peaks relative to each other, it is easy to conclude that the Earth is a sphere.

## Level, Higher and Lower

A higher position is farther up, away from the center of the Earth, relative to sea level. Conversely, a lower position is closer toward Earth’s center, relative to sea level. Two positions are level if they are at the same height from sea level.

Some flat-Earthers are unable to understand this. To them, ‘level’ means straight. They are wrong. In Earth sciences, height is measured from a plane of reference, usually the sea level.

## Suez Canal

The Suez Canal is a waterway connecting the Mediterranean Sea to the Red Sea. The level of water on both seas is practically the same, and the Suez Canal contains no locks system.

Flat-Earthers are claiming that the Suez Canal was constructed without accounting for curvature. They said if the Earth were spherical, then the middle of the canal should have been 1666 ft deep. This is merely a misconception. The surface of the water is equipotential. It has roughly the same distance to the Earth’s center of gravity. It is not necessary to dig 1666 ft in the middle of the Suez Canal. The engineers only need to ensure the base of the canal is below sea level for sea water to flow.

## The False Dilemma of the Figure of the Earth

There are several models explaining the figure of the Earth. These models vary in the way they are used, in their complexity and in the accuracy with which they represent the size and shape of the Earth. These models are sphere, ellipsoid, and geoid.

Flat-Earthers often take the existence of these multiple models as evidence of disagreement among scientists, and that the shape of the Earth is still in contention. They are wrong. All these models are valid models, only with different complexity and accuracy.

## Al-Biruni’s Method to Determine the Radius of the Earth

In the 11th century, Al-Biruni successfully determined the radius of the Earth. He accomplished that by measuring the dip of the horizon from the top of a hill. From the measurements, he was able to calculate the radius of the Earth.

In the 21st century, we can easily repeat the same experiment with practically no effort. We just need a smartphone and an opportunity to observe the horizon from a high altitude, like during a flight.

## Seismic Waves: Mapping the Interior of the Earth

Seismic waves are waves of energy that travel through the Earth’s layers and are a result of earthquakes, volcanic eruptions, massive landslides and large human-made explosions. Some types of seismic waves travel through the interior of the Earth and are detected by seismic stations on the other side of the Earth. By analyzing the types of waves that are received by seismic stations, we can determine the interior of the Earth.

Flat-Earthers are often seen saying that it is impossible to determine the interior of the Earth as nobody has gone there. They are wrong. Using seismology, we can determine the interior of the Earth without going there physically.

## The Earth is Spherical and The Nile Never Flows Uphill Anywhere

The Nile never flows uphill, or in other words, ascend to a location farther from sea level anywhere in the Nile basin.

Flat-Earthers often claim that if the Earth is spherical, then the Nile will have to flow uphill to overcome the curvature of the Earth. They are wrong.

## Grid Corrections — How the Spherical Figure of the Earth Affects Land Partitioning

Some countries decided to partition their territories into a rectangular or square grid. But the Earth is spherical, and it is not possible to divide a spherical surface into a perfect rectangular grid while maintaining the perfect angles, distances, and areas.

To solve this problem, land surveyors implemented grid corrections. Every certain distance, parts of the grid are shifted away from each other. Therefore, an equal area in each division is maintained as much as possible by giving up an entirely lined up grid.

If the Earth is flat, it is not necessary to have this compromise. It would be possible to divide the land into a perfect square grid system.

## “Earth is a Sphere” Semantic Games

The Earth is spherical, but not perfectly spherical. Its diameter is longer across the equator than between both poles. The shape is called ‘oblate spheroid’. The difference between both diameters is tiny, only about 0.33%. It is perfectly fine to say that the Earth is round or spherical.

Some flat-Earthers take this issue very seriously. They think if that’s the case, then we can’t say the Earth is spherical. They are wrong. If we can’t say the Earth is a sphere, then we can’t describe every other spherical object as spherical, because nothing is perfectly spherical.

## Neil deGrasse Tyson and His ‘Pear-Shaped’ Analogy

In a talk show, Neil deGrasse Tyson explained the figure of the Earth. He told the audience that the Earth is practically round, but it is a little farther from the center near the equator compared to the poles. And that in the southern parts, it is a bit farther from the center than in its northern regions. To illustrate the fact, Neil used the analogy ‘pear-shaped.’

Flat-Earthers really love to ridicule the ‘pear-shaped’ analogy. But they are mistaken. If they watch the entire unaltered video, they will find Neil explained the fact very clearly.

## The Earth is Spherical and The Mississippi River Never Flows Uphill Anywhere

The Mississippi River never flows uphill, or in other words, ascend to a location farther from sea level anywhere in the Mississippi River basin.

Flat-Earthers often claim that if the Earth is spherical, then the Mississippi River will have to flow uphill to overcome the curvature of the Earth. They are wrong.

## The Eratosthenes Experiment: Proving the Earth is Spherical

In 205 BC, Eratosthenes successfully determined the circumference of the Earth by measuring the length of the shadow cast by a rod. He did the measurement in Alexandria and timed it to coincidence when the Sun is directly overhead Syene.

2222 years after that, some flat-Earthers tried to refute the Eratosthenes experiment. They say the experiment can be applied to the flat-Earth model.

## The Earth is Spherical and The Amazon Never Flows Uphill Anywhere

The Amazon never flows uphill, or in other words, ascend to a location farther from sea level anywhere in the Amazon basin.

Flat-Earthers often claim that if the Earth is spherical, then the Amazon will have to flow uphill to overcome the curvature of the Earth. They are wrong.

## Equipotential: a Property of the Surface of Water

Gravity causes water to seek the lowest potential, which can be simplified as the position as close as possible to the Earth’s center of gravity. As a result, the surface of the water will have equipotential surface and form an approximately spherical surface which has the same center as the Earth. Every location along the surface has the same potential.