Because Earth is a sphere, the horizon always lies below eye level. We cannot see it near Earth’s surface with the naked eye. But with a precise instrument like a theodolite, we can observe the dip of the horizon.
Flat-Earthers claim that the horizon always rises to eye level. In reality, even from very close to Earth’s surface, it is still possible to observe that the horizon lies below eye level.
Continue reading “Theodolite and the Dip of the Horizon”
A ship disappearing from the bottom first is an effect of Earth’s curvature. It is not a direct observation of the curve itself. We can only directly see the curve from a high altitude, not from near the surface.
Flat-Earthers present this reality as if it is a dilemma: 1. Earth is too big for us to see the curvature, but 2. We can see ships go over the curvature. It is a false dilemma. Ships disappearing from the bottom first is an effect of Earth’s curvature. Such an observation is different from directly witnessing the curve itself.
Continue reading “Curvature Dilemma”
Because of a perspective effect, an observer in space can see more of Earth’s surface if they are farther from Earth.
Flat-Earthers noticed the different visible Earth’s surface in different Earth images and used it to “prove” they are fake. In reality, it is just a perspective effect caused by the fact that the Earth was seen from a different observer distance.
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A selenelion is a rare lunar eclipse where the Sun and the Moon are both visible at the same time. An even rarer form of selenelion occurs if it is a partial lunar eclipse, and the upper part of the Moon is eclipsed. Some call this an “impossible eclipse.”
Flat-Earthers claim that such an eclipse should not be possible to occur because the Earth’s shadow is in the wrong position. In reality, it is possible to happen because the observer is looking slightly downward due to the dip of the horizon and atmospheric refraction.
Continue reading “The Impossible Eclipse”
If a distant boat is not visible, then it is because of at least one of these reasons:
- Our eyes have limited angular resolution and are unable to resolve the ship at that distance.
- The atmospheric condition is limiting our visibility.
- The curvature of the Earth obscures the ship.
Flat-Earthers like to demonstrate that a previously invisible ship at a distance can be made visible by zooming in. They would use it to disprove Earth’s curvature. They are wrong. There are reasons other than Earth’s curvature that can obscure a distant boat.
Continue reading “Zooming In On Distant Boats Does Not Disprove Earth’s Curvature”
The fallacy of ‘appeal to definition’ is using the definition of a term to support an argument as if the term cannot have other meanings or even conflicting meanings. Flat-Earthers often use this fallacy, for example, over the word “theory.”
A communication problem can occur when a term gets misinterpreted to mean other than what was intended. A simple clarification should quickly correct the problem. The appeal to definition arises if the clarification is refused, and the person insists on using the wrong & unintended meaning of the term, and use it to support their arguments.
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We can determine if a star is visible from a specific location using the declination of the star and the latitude of the observer, subject to other conditions like observer’s topology, the magnitude of the star, weather conditions, etc. It is possible to do this because Earth is a rotating sphere.
If the Earth is flat, every star would have been visible all night from every location. We don’t see the same stars every night because some of them are below the horizon and obscured by the Earth.
Continue reading “Determining the Visibility of a Star From Its Declination and the Observer’s Latitude”
Due to Earth’s curvature, ships traveling over an ocean disappear from the bottom up. This fact is one of the first evidence to confirm the Earth is a sphere, and one of the first facts of which flat-Earthers had to invent various “explanations” for.
Some of the popular “explanations” are: refraction, perspective, zooming reveal distant ships and visibility limitations. None can explain away the fact.
Continue reading “Ships Disappearing Over the Horizon and the Various “Explanations” Invented by Flat-Earthers”
A circumpolar star is a star, as viewed from a given latitude on Earth, that never sets below the horizon due to its apparent proximity to one of the celestial poles. Circumpolar stars stay up there in the sky, even during the day.
Flat-Earthers claim the Earth is stationary because the same stars are always visible in the sky. They are wrong. Only circumpolar stars are always in the sky. There are others that are not circumpolar. Some are only visible during certain times in a year.
Continue reading “Circumpolar and Non-Circumpolar Stars”
Astrolabe is an astronomical instrument for measuring the altitude of the sun or stars, and to determine the solution of various problems in astronomy, time, and navigation. Astrolabe was used from classical antiquity, about 2nd century BC, until the age of discovery where it was superseded by the more accurate sextant, star charts, and time-keeping devices.
Flat-Earthers claim that astrolabes can only work because the Earth is flat. They are wrong. Astrolabes were designed using the spherical Earth model. To use an astrolabe, a good understanding of the spherical Earth model is required.
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There are two kinds of the horizon:
- Astronomical horizon: the horizon at the eye level.
- True horizon: the line that visually divides the Earth and the sky.
Because the Earth is a sphere, the true horizon always lies below the astronomical horizon, or the eye-level. The angle between them is the dip of the horizon. The higher the observer, the larger the dip of the horizon.
Flat-Earthers claim there’s no dip of the horizon. They are wrong. It is not hard to observe the drop of the horizon and prove the curvature of the Earth.
Continue reading “The Dip of the Horizon”
A crow’s nest is a structure in the upper part of the ship, especially old-fashioned ones. It is used as a lookout point and positioned high above to increase visibility over the curvature of the Earth.
On the deck of a ship 4 m (13 ft) above the surface of the ocean, an observer can spot a 20 m (66 ft) high ship from at most ±25 km (16 mi). On the other hand, from a 35 m (115 ft) high crow’s nest, an observer will be able to spot the same ship from ±40 km (25 mi) away.
Continue reading “Crow’s Nest on Ships”
We can’t directly observe and subjectively perceive the curvature of the Earth from a position close to the surface. And this matches the expectations in the spherical Earth model.
Flat-Earthers often take the fact we can see the curvature by standing on a beach as ‘evidence’ the curve doesn’t exist. They are, once again, wrong.
Continue reading “The Reason We Cannot See Earth’s Curvature When Standing on a Beach”
A fisheye lens distorts images. It results in images having barrel distortions. In a fisheye lens, a straight line can appear curved. But some flat-Earthers don’t realize that the opposite is also true, a fisheye lens can easily make a curved line look straight.
Continue reading “Fisheye Lenses Can Make Curved Lines Appear Flat”
Light waves are not always moving in a straight line. When it passes through a medium of a different refractive index, the waves will deviate. The phenomenon is called refraction and described according to Snell’s Law.
Earth’s atmosphere has variation in air density that depends on the altitude. As the refractive index changes with the density of the medium, light waves passing through Earth’s atmosphere also experience refraction.
Continue reading “Atmospheric Refraction”
Having the total height of about 830m, Burj Khalifa is the tallest building in the world. It is so tall that we can observe the sunset at the base of the building, then rush to the upper floors and watch the same sunset again for the second time on the same day.
This phenomenon can only happen if the Earth is a sphere. On a higher position, we will observe the sunset later than when we are closer to the ground.
Continue reading “Sunset at Burj Khalifa”