The Big Dipper is a bright asterism in the northern celestial sphere. It is always visible north of 41°N and hidden south of 41°S. Flat-Earthers noticed that the Big Dipper is visible all year and use the fact to ‘prove’ a flat Earth. In reality, the visibility of Big Dipper depends on the latitude of the observer.
The Sun is 1,391,016 km (864337 mi) in diameter and 146,600,000 km (93,000,000 mi) from us. These facts are consistent with everyday observations.
Flat-Earthers have a different idea about the distance and the size of the Sun. However, on careful examinations, the numbers are inconsistent with everyday observations.
Light travels in a practically straight line over a short distance. We often use this property of light to determine if an object is flat or straight from visual observation.
Some flat-Earthers start with the wrong assumption that a specific object is flat, then attempt to redefine how our vision works from that. They are wrong. From visual observation, we can determine if an object is flat, not the other way around.
The angle (or altitude) to Polaris approximately corresponds to the latitude of the observer. This fact is observed on every location on Earth where Polaris is visible.
By tracing the path to Polaris from multiple locations on the flat Earth model, the lines will not point to a consistent position of Polaris. The reason is that the Earth is a sphere and the flat Earth model does not represent reality.
Observing Earth’s curvature is more difficult when we are too close to Earth’s surface. The highest place within reach of the general public is a commercial passenger flight. Even then, it is still difficult to casually discern the curvature of the Earth from an airplane. With some effort, it is possible to observe the curve of the Earth from a location closer to the surface, as long as we are willing to do some planning and careful observation.
Stars are not visible in photos of the Moon –including those taken from the lunar surface— because the Moon is sunlit. The exposure needed to take a photograph of the Moon is not that much different from that used to take a photo in daylight on Earth’s surface.
To demonstrate this, we can try taking a picture of the Moon with stars visible, on the conditions: 1. The lunar features, like the craters, are correctly exposed, not overexposed. 2. Taken in a single exposure, not HDR, and not the result of editing. Even if we are using the best camera available today, the stars can’t show up in large enough quantity.
Everyone on Earth observes the same face and phase of the Moon at the same time, provided the Moon is visible from the location of the observer. This fact is contrary to what the flat Earth model requires. It rules out the possibility of a flat-Earth and that the Moon is a sphere hovering a few thousand miles above Earth’s surface.
Different locations on a comparable latitude can have some similarities. However, the latitude is not the only factor that decides seasonal changes, biodiversity, temperatures, and other conditions. The conditions can be vastly different even on places on the similar latitudes.
Flat-Earthers highlight the differences between locations on a similar latitude to the North and South of the Equator and conclude Earth must be flat. They are wrong. There are factors other than latitude that determine the differences.
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.
Muslims perform their prayers by facing the Qibla —or the direction to the Kaaba in Mecca, Saudi Arabia. The direction of the Qibla is traditionally determined from the direction to the Sun when the Sun is directly overhead the Kaaba. If during the time the Sun is visible, it will indicate the direction of the Qibla.
If the results of the observation are drawn on the so-called ‘flat-Earth map’, the Qibla will not consistently point to the Kaaba. Only the calculation using the spherical Earth model will give us consistent results that conform to centuries of observation, from various locations on Earth. The reason is that the Earth is a sphere.
Because the Earth is a sphere, the surface of Earth obstructs distant enough objects. Climbing to a higher altitude allows us to see farther and more of the previously obstructed objects will become visible, starting from the tops first.
This phenomenon would not occur if the Earth were flat. In a flat Earth, it would not be possible for Earth’s surface to obstruct more of an object —starting from the bottom portions first— if the observer is closer to the surface.
The same thing also happens for objects nearby a large body of water. The surface of the water —which is obviously lower than the object— can obscure the object if the viewer is far enough. Flat-Earthers often invent the “explanation” that Earth’s contour causes the obstruction. This phenomenon can easily prove them wrong.
The Cavendish experiment was the first experiment to measure the force of gravity between masses in the laboratory and the first to yield accurate values for the gravitational constant.
Flat-Earthers are in a constant effort to discredit the Cavendish experiment. They would invent various “explanations” to “explain” the result of the experiments. However, the experiment was not only done once by Henry Cavendish in 1797-1798, and has been replicated numerous times by multiple independent parties for centuries, all yielding consistent results.
On many flights, they would give away leveling devices to all passengers for free, so that everyone would be able to observe the dip of the horizon and proves Earth is a sphere. And as a nice side effect, to quench our thirsts, too!
Such devices are called ‘bottled water’. Using these simple ‘instruments’ on a flight, we can demonstrate that Earth is a sphere.
Earth’s curvature is hard to observe from the surface. Even from the altitude of a commercial passenger flight, about 30000-40000 ft, Earth’s curvature is still too small to notice. However, under careful observation, it is not impossible to confirm the curve from the cruising altitude of a jet airliner.
If the Earth were flat, then the Sun has to be visible above the horizon all the time, from the entire Earth. This does not occur, and the simple fact should have been sufficient to rule out any possibility of a flat-Earth.
But instead, flat-Earthers invented various convoluted chain of ad-hoc hypotheses and presented them as “explanations” to prevent the flat-Earth model from being falsified. None of the “explanations” are proven nor correspond to the way our world works.
The apparent size of the Moon remains constant in a single day. This can only happen if the Moon is practically at the same distance all day.
In the flat-Earth model, the Moon is thought to be moving in a circle above the flat Earth. Such a notion should cause the Moon apparent size to vary in a day. However, in reality, the Moon appears in the same size all day, and it proves that the flat-Earth model does not represent reality and that the Moon is much farther.
The Moon is tidally locked. Half of the Moon is always facing the Earth. However, due to libration, we can take a glimpse of areas of the moon that are not always visible.
Flat-Earthers invented many “scenarios” to “explain” how the so many lunar-related phenomena can happen on the flat Earth model. Some of these “explanations” include “transparent Moon”, “hemisphere-shaped Moon”, “flat circular Moon”, etc. Lunar libration rules out the majority, if not all, of these “explanations.”
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.
At any time, the Sun illuminates one half of the Moon and the other half dark. The phase of the Moon is the shape of the sunlit portion of the Moon as viewed by observers on Earth.
The phase of the Moon can never be adequately explained using the flat Earth model. To deal with this inconsistency in their theory, some perpetrators of flat Earth invented an ‘explanation’ that the phase of the Moon is not caused by sunlight. They are wrong. We can observe the Moon very carefully using telescopes of high-zoom cameras, and it will be evident how the lunar craters are lit. And this can only happen if the Moon is sunlit.
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.