Sun Outage

A Sun outage is a disruption of geostationary satellite signal caused by interference of the sun when it falls directly behind a satellite with which a receiver is communicating. Sun outages occur around the March equinox and September equinox.

Flat-Earthers fail to understand how the schedule of a Sun outage depends on the satellite and the receiver’s location. And they use it to discredit the fact. In reality, it is not difficult to visualize how a Sun outage occurs, and it will be consistent with the expectation.

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Observing Mercury and Venus

Mercury and Venus are inferior planets. Their orbits are closer to the Sun than Earth. We can see these planets if they are above the horizon, and it will be easier if the Sun is below the horizon. Generally, both planets can be seen early or late in the night.

Flat-Earthers claim we should not be able to see Mercury and Venus as they are closer to the sun, and at night we are facing away from the sun. In reality, early and late in the night, we can look toward the general direction of the Sun & observe both planets.

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Geometry of a Full Moon

Some people are confused that we can see a full moon all night. They expect if the full moon is the result of the opposition of the moon from the sun, then a full moon should be visible only at midnight.

Flat-Earthers with such a spatial cognition problem go a step further and use it to “disprove” spherical Earth. In reality, we can easily explain the phenomenon in the spherical Earth model.

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ISS Size Compared to an Airplane in a Photograph

Flat-Earthers compared the apparent size of the ISS and an airplane that appeared in photographs and then incorrectly concluded that the ISS could not be 410 km above us. Their mistake was equating altitude with distance and failing to account for both the ISS’ and the airplane’s downrange distance.

If an airplane is at an altitude of 12 km, it does not mean its distance from an observer is also 12 km. Its altitude and distance are equal only if the airplane is directly above the observer. If the plane is not directly above, then its distance is greater than its altitude.

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Solar Eclipse: Length of the Umbra & Earth-Moon Distance

The distances to the Sun and the Moon are 149,600,000 km and 384,400 km. These figures are average values, and the actual values are around these averages. In a solar eclipse, the actual distances determine whether a total or annular solar eclipse occurs.

Flat-Earthers calculated the geometry of a solar eclipse using these average distances and discovered the umbra does not reach Earth’s surface. They wrongly concluded that an eclipse should not occur. In reality, the numbers are only averages, not the real values. And if the umbra does not reach Earth’s surface, it will still produce an annular solar eclipse.

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Ursa Minor

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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 Impossible Eclipse

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.

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Umbra, Penumbra, and Antumbra in an Eclipse Diagram

Light generally travels in a straight line. We can use this property of light to determine the umbra, penumbra, and antumbra part of a shadow by drawing lines from the edges of the light source toward and past that of the occluding object.

Flat-Earthers regard the lines in an eclipse diagram as a violation of the fact that a light source emits light in every direction. In reality, the lines are there only to determine the boundaries of the shadow’s regions in an eclipse diagram.

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Orion

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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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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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Crux

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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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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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Visibility of the Moon from Two Opposing Locations on Earth

Some flat-Earthers are confused that two observers on the opposing locations on Earth can observe the Moon at the same time, and they would use it as ‘proof’ that the Earth is not a sphere. It is merely a spatial cognition problem by the flat-Earthers.

Any observer on Earth’s surface has 180° vertical field of view over the entire sky. They can observe objects low on the horizon, not just objects above them. Observers on the opposing sides of the Earth would have no problem seeing the Moon at the same time.

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Lunar Phase: Earth’s Shadow has Nothing to do with It

It can be surprising that many people believe that the lunar phase is caused by the Earth casting its shadow on the surface of the Moon. Flat-Earthers are no exception. But they take it one step further and use the misconception do “disprove” the fact that Earth is a sphere. They are wrong. The lunar phase is the shape of the sunlit part of the Moon seen from the observer.

On the other hand, the phenomenon where the Earth casting its shadow on the surface of the Moon is called the lunar eclipse. Moon phase occurs all the time and undergoes a monthly cycle, while a lunar eclipse happens only a couple times in a year.

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The Varying Earth-Moon Proportions in Different Pictures

How an object appears in a photograph depends on perspective —the position of the camera relative to the object—, and field of view of the camera. The farther the object, the smaller the object will appear in the resulting image; and conversely, the closer the object, the larger it will appear. The narrower the field of view, the larger the object will appear in the image; and conversely the wider the field of view, the smaller the object will appear.

Flat-Earthers take the varying proportions of the Earth & Moon in different pictures as a glaring inconsistency. They are wrong. The pictures were simply taken from a different perspective and field of view.

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Determining the Visibility of a Star From Its Declination and the Observer’s Latitude

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.

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Observations of Sunspots From Multiple Locations on Earth

Sunspots are darker spots on the surface of the Sun. The location where sunspots appear is unpredictable, but the appearance of sunspots is always the same when observed from anywhere on Earth; only the orientation is different on different observer location. Observers on the opposite position on the Earth will see the sunspots reversed. The reason is that the Earth is a sphere. Any two observers on Earth’s surface are not standing on the same plane.

Some flat-Earthers have spatial awareness difficulties and present the difference of the appearance of sunspots as ‘evidence’ the Earth is not spherical. They are wrong. If the Sun were close as in the flat Earth model, we would see the different appearance of sunspots on the different observer location. In reality, everyone on Earth observes the same appearance of sunspots, only with the different orientation that corresponds to the position of the observer.