Planets are not stars. On casual observation, both planets and stars appear as bright dots in the night sky. But with careful observation, we know planets are different from the stars.
Flat-Earthers insist that planets are just stars. In reality, we can easily observe many of the planets’ attributes that set them apart from the stars —using minimal efforts and equipment.
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Airy’s Failure was an experiment performed in 1871 in which Sir George Biddell Airy failed to confirm the aether theory by measuring stellar aberration. The phenomenon of stellar aberration, in itself, was the first direct evidence of Earth’s motion around the sun.
Flat-Earthers claim that the “failure” in “Airy’s Failure” is the failure of proving the motion of Earth. In reality, the experiment aimed to confirm the aether theory. The “failure” was in proving the aether theory. The experiment relied on the already accepted knowledge that Earth is in orbit around the sun.
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It is not impossible to build our own telescopes instead of buying off-the-shelf ones from a manufacturer. Amateur telescope making is a sub-group in the field of amateur astronomy where people build telescopes for personal enjoyment.
Some flat-Earthers claim that telescopes are programmed by the manufacturer to display fabricated images to the user. The possibility of making our own telescopes tells us that such a claim is false and ridiculous.
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Axial precession is the change in Earth’s rotational axis. It is a slow change with a cycle of 25772 years. As a result, the role of pole star will pass from one star to another.
Contrary to flat-Earthers’ assertions, due to Earth’s axial precession, Polaris has not always been the North Star and will not remain as the North Star. The star Gamma Cephei will replace Polaris’ place in 2000 years as the North Star.
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Ursa Minor is a constellation in the Northern Sky. It is traditionally important for navigation because of one of its member stars, Polaris, being the north star. Ursa Minor is always visible north of the 18°N and hidden south of 18°S. Polaris is located very close to the North Celestial Pole, and only visible north of the Equator. The visibility of Ursa Minor and Polaris is only consistent if Earth is a sphere.
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The pole star Polaris is used to locate the position of the north celestial pole because it is a bright star that is conveniently located very close to it. However, there is no corresponding bright South Star near the south celestial pole. To locate the south celestial pole, we need to observe stars around it.
There is no South Star as useful as Polaris in the north. Flat-Earthers use it to “disprove” the existence of the south celestial pole, which cannot possibly exist if Earth were flat. In reality, the south celestial pole can be easily shown and located. There is simply no bright star near it.
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Angular resolution is the minimum separation between distinguishable features in an image. Objects smaller than the angular resolution are indiscernible in the picture. The theoretical maximum angular resolution is determined by the diameter of the aperture of the optical instrument.
Flat-Earthers like to demand images of the lunar landers taken with a telescope as proof that the Apollo Moon landings did occur. In reality, no optical telescope on Earth is large enough to resolve the landers.
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The Solar System is in motion around the Milky Way galaxy, while the planets in the Solar System are in orbiting motion around the sun. As a result, from an observer outside the Solar System, planets will appear to move in a helical motion. Someone created an animation of this helical motion; it went viral and had a lot of media attention.
Flat-Earthers noticed the animation and use it to reinforce their arguments. They claim if the animation is correct, then stars should appear moving & star trails should be impossible. In reality, the animation does not show us the vast distances to the stars.
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Apparent motion is the appearance that celestial objects move due to the motion of Earth. If all the objects that appear in the sky are moving similarly, then it is far more likely that the movement is only apparent and caused by the motion of the observer.
Flat-Earthers claim that the motion of celestial objects “proves” that Earth is stationary, and the celestial objects are moving. By the same “reasoning,” we can conclude that the train we are in is stationary, it is just all the objects outside, as luck would have it, are moving in a very similar fashion.
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Stellar aberration is the apparent shift of stars about their actual positions, depending on the direction Earth is moving in its orbit around the sun. It occurs because the speed of light is finite; it takes time for light to reach the observer.
Stellar aberration was discovered in 1727 by James Bradley. It was the first direct proof of heliocentrism, that Earth is in orbit around the sun.
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Stellar parallax is the apparent shift of the position of a nearby star against the background of distant stars. It is the result of Earth’s orbital motion around the Sun. It is tiny and difficult to observe. Successful measurement of stellar parallax was done only after the 19th century.
Some flat-Earthers claim that stellar parallax has never been successfully observed, and they use it as ‘evidence’ Earth is stationary. In reality, stellar parallax has been successfully measured in 1838 and is now used as the basis for measuring stellar distances.
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Proper motion is the apparent motion of stars, caused by the movement of the stars themselves, relative to the solar system. Stars will appear to shift over time, relative to other, more distant stars.
Flat-Earthers assume stars are only in motion around Polaris, or the north celestial pole. They are wrong. Stars have other apparent movements, one of which is proper motion.
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The Andromeda Galaxy is the nearest major galaxy. It is visible to the naked eye on dark nights and the easiest deep-sky object to capture even without special equipment.
There are many images of Andromeda on the Internet because it is not that hard to capture it. Flat-Earthers assumed the pictures are the Milky Way and immediately claimed those pictures as fakes. In reality, the galaxy in the photographs is the Andromeda, and it is not hard for anyone to take a picture of it. The “you are here” sign on some pictures of the Andromeda Galaxy is silly and an obvious spoof. It was merely an attempt on a joke.
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In 24 hours, the Earth makes slightly more than one full rotation due to its motion around the Sun. We call it one day or one synodic day. On the other hand, a sidereal day is the period of one rotation relative to distant stars.
Flat-Earthers claim that if the Earth is in orbit around the Sun, after six months, at the same hours, then the day would turn into night and night would turn into day. In reality, it would have been true if we are using sidereal day, not synodic day, or just “day” in our everyday language.
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On each day, we can observe stars to drift about 1° in their motion around the celestial pole. In a month, they will appear to have moved about 30° when observed at the same time in the night. In a year, they will be back to their original positions as the same day in the previous year. The observation is the basis of the solar calendar system we are using today.
Some flat-Earthers claimed that the stars appear the same every night, and they would erroneously conclude that the Earth is stationary. In reality, stars are shifting about 1° every day.
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Orion is a prominent constellation located on the celestial equator, and therefore, visible throughout the world. The angle Orion makes during rising and setting corresponds to the observer’s latitude, and so does its altitude during culmination. All the observations are only consistent if Earth is a sphere.
Flat-Earthers claim the visibility of Orion from the entire world disproves spherical Earth. This only comes from their difficulty in understanding the geometry involved. By understanding Earth’s rotation and where Orion is located, it is not hard to conclude that the visibility of Orion is consistent with the spherical Earth model.
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Due to its almost +90° declination, Polaris practically cannot be seen from the south of the equator, and the fact is consistent only with the spherical Earth model. There is a prevalent myth in the flat-Earth community that claims Polaris is sometimes visible from the south of the Equator. The origin of the myth was an erroneous interpretation of a news article by flat-Earther Samuel Rowbotham, 1½ centuries ago.
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The Sweden Solar System is the largest scale model of the Solar System in the world. We can use it to get a better sense of the sizes and distances in the Solar System.
Flat-Earthers like to claim that we never see a scale model of the Solar System, and use it to “prove” the failure of science to explain the world. The Sweden Solar System proves them wrong, and also gives us an idea about the problem of making a scale model of the Solar System.
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Some people are confused that the crescent moon can be visible at night, even though during the time, the Moon is closer to the Sun than Earth, and the part of the Earth is facing away from the Sun.
Many flat-Earthers have the same visualization difficulties, but they take it a step further and use it as ‘evidence’ as a ‘failure’ of science to explain the fact. In reality, the phenomenon can be readily explained in the spherical Earth model.
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The Southern Cross or Crux can be observed from the south of 26°N, and it is always visible south of 26°S. On a flat Earth, it should be visible from the outer parts on Earth at the same time, but not from the central areas, disproving the flat model. The visibility of Crux is only consistent with the spherical Earth model.
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