Angular Resolution

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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Helical Motion of Planets

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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

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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

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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

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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

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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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Andromeda Galaxy

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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Synodic Day vs Sidereal Day

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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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Star’s Annual Motion

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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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The Myth That Polaris is Visible South of the Equator

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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Sweden Solar System

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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Geometry of a Crescent Moon

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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Stars in the Southern Sky: Evidence That the Earth is a Rotating Sphere

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If we look south in any location in the southern hemisphere, we will see the same set of stars. The stars are seen rotating around the south celestial pole, in the Octans constellation, near the star Sigma Octantis.

This phenomenon can never be explained in the flat-Earth model. Looking at the so-called ‘flat-Earth map’, we should see another set of stars on a different location in the southern hemisphere. The reason is that the flat-Earth model is a false representation of the Earth.

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Ptolemy’s Almagest and Earth’s Axial Precession

Due to Earth’s axial precession, the positions of Earth’s celestial poles shift gradually in a cycle of approximately 26000 years. These days, Polaris is very close to the north celestial pole. However, 19 centuries ago, Kochab is much closer to the celestial pole than Polaris.

Flat-Earthers claim that the stars are always in the same position proves the Earth is stationary. An ancient star chart like Almagest from the 2nd century shows them wrong. The stars today were not in the same place as stars 19 centuries ago.

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Big Dipper

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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.

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Polaris Altitude from Multiple Locations on Earth

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.

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The Moon and Stars in a Single Picture

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.

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An analemma is a photograph or diagram showing the position of the Sun in the sky, as seen from a fixed location on Earth at the same mean solar time, as that position varies over the course of a year. The diagram will resemble the figure 8.

The north-south component of the analemma results from the change in the Sun’s declination due to the tilt of Earth’s axis of rotation. The east-west component results from the non-uniform rate of change of the Sun’s right ascension, governed by the combined effects of Earth’s axial tilt and orbital eccentricity.

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