Sun Observation
En una Tierra plana, un Sol que brilla en todas las direcciones iluminaría toda la superficie al mismo tiempo, y todos los lugares experimentarían el amanecer y el atardecer en el horizonte aproximadamente al mismo tiempo. Con una Tierra esférica, la mitad del planeta está a la luz del día en un momento dado y la otra mitad experimenta la noche. Cuando una ubicación dada en la Tierra esférica está a la luz del sol, su antípoda –la ubicación exactamente en el lado opuesto de la Tierra– está en la oscuridad. La forma esférica de la Tierra hace que el Sol salga y se ponga a diferentes horas en diferentes lugares, y diferentes lugares reciben diferentes cantidades de luz solar cada día.
Para explicar el día y la noche, las zonas horarias y las estaciones, algunos conjeturadores de la Tierra plana proponen que el Sol no emite luz en todas las direcciones, sino que actúa más como un foco, iluminando solo una parte de la Tierra plana a la vez.[56][57] Esta conjetura no es consistente con la observación: al amanecer y al atardecer, un Sol reflector estaría en el cielo al menos un poco, en lugar de en el horizonte donde siempre se observa. Un Sol reflector también aparecería en diferentes ángulos en el cielo con respecto a un suelo plano que con respecto a un suelo curvo.
Suponiendo que la luz viaja en línea recta, las mediciones reales del ángulo del Sol en el cielo desde ubicaciones muy distantes entre sí solo son consistentes con una geometría en la que el Sol está muy lejos y se ve desde la mitad diurna de una Tierra esférica. Estos dos fenómenos están relacionados: un Sol reflector a baja altura pasaría la mayor parte del día cerca del horizonte en la mayoría de los lugares de la Tierra, lo cual no se observa, pero sale y se pone bastante cerca del horizonte. Un Sol a gran altura pasaría la mayor parte del día lejos del horizonte, pero saldría y se pondría bastante lejos del horizonte, lo que tampoco se observa.
Sunrise and sunset
One difficulty with the flat Earth model is describing why the sun appears and disappears completely at night. The flat earth model maintains that the Sun is small and rotates around above the planet in a clockwise direction. This would imply that this star would always be visible, since it is constantly above the Earth, but it is during sunset when the Sun crosses the plane of the horizon and passes from the visible to the non-visible hemisphere, thus producing night with its absence.[58][19].
Some flat earthers invoke perspective and vanishing points to explain the occultation of the Sun, but perspective does not allow an object to be completely below the horizon if it is above it.[58][59].
Another answer is to claim that this phenomenon is an optical illusion produced by atmospheric refraction via a lower mirage, which requires less dense (warm) air just above the surface to refract the rays upward. However, the air at the Earth's surface is generally denser (colder), producing a superior mirage in which light bends downward (Fig. 17), causing the Sun (and Moon; see: eclipse selenelion) to appear approximately higher than its true position "a little more than half a degree lower than it appears as a result of this effect" (Fig. 18)[60] (See: false dawn and dusk). In addition, mirages produce turbulence or distortion in objects and only appear half a degree near the horizon. Because climatic conditions constantly vary, refraction is not an adequate explanation of this phenomenon either.[59][61][62].
Another observation described by Ptolemy in his Almagest as proof of the sphericity of the Earth is that "the Sun, the Moon and other stars do not rise and set simultaneously for everyone on the Earth, but do so earlier for those [found] further to the East, later for those towards the West."[63].
Changing the length of the day
Another piece of evidence for the sphericity of the Earth is based on the observation that the maximum day length increases with increasing latitude. The first person to measure latitude by the maximum length of the day was Pytheas.[43] Pliny the Elder described this observation in Historia natural "Natural history (work of Pliny)")[64] and Ptolemy in his Almagest.[6].
On a flat Earth with an omnidirectional Sun, all places would experience the same amount of daylight every day, and all places would receive daylight at the same time. The actual length of the day varies considerably, with places closer to the poles having very long days in the summer and very short days in the winter, with the northern summer occurring at the same time as the southern winter. Locations north of the Arctic Circle and south of the Antarctic Circle receive no sunlight for at least one day per year and receive 24-hour sunlight for at least one day per year. Both poles experience sunlight for 6 months and darkness for 6 months, at opposite times.
The movement of daylight between the northern and southern hemispheres occurs due to the axial tilt of the Earth. The imaginary line around which the Earth rotates, which runs between the North Pole and the South Pole, is inclined about 23° with respect to the oval that describes its orbit around the Sun. The Earth always points in the same direction when it moves around the Sun, so during half the year (summer in the northern hemisphere), the North Pole points slightly towards the Sun, keeping it in daylight all the time because the Sun illuminates the half of the Earth that is in front of it (and the North Pole is always in that half due to the inclination). For the other half of the orbit, the South Pole is slightly tilted toward the Sun and it is winter in the Northern Hemisphere. This means that at the equator, the Sun is not directly overhead at noon, except around the March and September equinoxes, when a point on the equator points directly at the Sun.
Length of day beyond the polar circles
Due to the tilt of the Earth's axis of rotation, the length of the day varies. As the Earth rotates, some places (near the poles) pass only a small bend near the top or bottom of half the sunlight; Other places (near the equator) travel along much longer curves through the middle. In places outside the polar circles, there are so-called "midnight suns" in midsummer, in which the sun is never more than a few degrees below the horizon in June, so that a bright twilight persists from dusk to dawn.[66] In Russia, Saint Petersburg uses this phenomenon in its tourism marketing.[67].
Twilight Duration
Longer twilights are observed at higher latitudes (near the poles) due to a smaller angle of the Sun's apparent motion compared to the horizon.
On a flat Earth, the Sun's shadow would reach the upper atmosphere very quickly, except near the Earth's nearest edge, and would always make the same angle with respect to the ground (which is not what is observed).
The length of twilight would be very different on a flat Earth. On a round Earth, the atmosphere above the ground lights up for a time before sunrise and after sunset they are observed at ground level, because the Sun is still visible from higher altitudes.
The "Spotlight Sun" conjecture is also not consistent with this observation, since air cannot be illuminated without the ground beneath it also being illuminated (except for the shadows of mountains, skyscrapers, and other surface obstacles).
Apparent size of the Sun
In the flat Earth model, the Sun is small and rotates around the planet together with the Moon clockwise. Then, sunrise and sunset would be products of perspective when the Sun approaches or moves away from the Earth in the same way that the streetlights on a long street seem to hide in the distance. Consequently, the apparent size of the Sun would change throughout the day, growing larger until midday and decreasing until sunset.
The apparent size of the Sun is constant throughout the day. This is because the Sun is actually about 90 million kilometers away, which means that its size barely changes during the day. During the year the solar semidiameter varies between a minimum of 15' 45" at apogee and 16' 17" at perigee.
One argument in support of a flat Earth is time-lapse videos of sunsets where the Sun appears to be waning. This is actually a product of the camera's glare in sunlight. To avoid this effect, you must adjust the camera's exposure "Exposure (photography)" manually and use solar filters (Fig. 19).[68][69].
This phenomenon also occurs with the Moon,[68] although it is erroneously stated that its size increases when it approaches the horizon. This is an optical illusion called the "moon illusion."
A common response from flat Earth advocates is that atmospheric refraction "makes the Sun and Moon look larger as they move away,"[70] but there is no evidence to support such a mechanism,[71] and it would apparently only affect celestial bodies (the Sun and Moon) but not other objects in the sky, such as aircraft. Atmospheric refraction can distort the solar and lunar disk, flattening its apparent vertical diameter as it approaches the horizon but the horizontal diameter remains constant (Fig. 20).
It has been theorized that due to the sphericity of the Earth, the atmosphere curved around its surface would act as a natural magnifying lens that would allow astronomical objects seen from about 1,360,000 km from the Earth to be magnified, a concept called "terrascope".[60].
daytime movement
As stated above, the Sun rotates clockwise around an axis passing through the North Pole on Earth according to the flat-earther model (Fig. 21). To explain seasonal temperature differences and the amount of sunlight each day it is argued that its radial distance changes throughout the year, being smallest at the summer solstice (moving along the Tropic of Cancer) and largest at the winter solstice (moving along the Tropic of Capricorn). Because of this, in the southern hemisphere the Sun would always be north everywhere on the December solstice, but this is not the case, since in countries like South Africa and Australia you can see the sunrise in the southeast and the sunset in the southwest. This observation fits the model of a round Earth with a tilted axis of rotation (see top right image).[72].
In this model the Sun would also be seen spinning clockwise in the sky when looking west during a sunset anywhere in the world (like the lights and columns in the second image below), but this prediction does not fit the observations. Due to the Earth's rotation, the Sun moves in arcs during the day, but its trajectory varies with respect to the position from where it is observed due to the sphericity of the Earth (Fig. 22).
Taking the central diagram (Fig. 24) as a reference, in the northern hemisphere north is to the left. There the Sun rises in the east (far arrow), culminates in the south (on the right) while moving to the right (Fig. 23) and sets in the west (near arrow). Both the starting and setting positions move towards the north in the middle of summer and towards the south in the middle of winter. On the other hand, in the southern hemisphere, south is to the left. The Sun rises in the east (near arrow), culminates in the north (on the right) while moving to the left (Fig. 25) and sets in the west (far arrow). Both the rising and setting positions move southwards in midsummer and northwards in midwinter.[73][74].
At the Earth's equator, the Sun sets vertically perpendicular to the horizon. In contrast, during the solstices the Sun does not set at one of the Earth's poles, which is called midnight sun (and polar night respectively, the opposite phenomenon, in which the night lasts more than 24 hours at the opposite pole). These two phenomena cannot be explained according to the flat Earth hypothesis.[75].
Observation of sunlight before or after seeing the Sun
From ground level it is possible to see the windows of nearby tall buildings illuminated by the sun a few minutes before seeing the sun rise or after watching the sun set. On a flat, non-curved Earth mass, it would only take a few seconds, due to a minuscule ratio (compare ~45 meters / 150 feet of a 14-story building with intercontinental distances). If such a phenomenon were caused by a prismatic property of the atmosphere on a flat world, with a relatively small light source rotating around the Earth (as in later maps of the flat Earth, dated 1800), it would contradict one's ability to see. a proper panorama of the starry sky at one point in the night, rather than a small but distorted "stretched" patch. Likewise, the top of a mountain is illuminated first at dawn and finally at dusk (Fig. 26 and 27). Even the Sun can project the shadow of the mountain in the sky (Fig. 28). This phenomenon is similar to the shadow of the Earth projected in the sky when the Sun hides below the horizon (Fig. 29).
Similarly, higher altitude clouds are illuminated before dawn and after dusk, as in the case of polar or noctilucent mesospheric clouds (Fig. 30).
On level ground, the difference in distance from the horizon between lying down and standing is large enough that you can see the Sun set twice by quickly rising immediately after seeing it set for the first time while lying down.[79] This can also be observed from a lifting platform,[80] a skyscraper (Fig. 31),[81][82] a mountain,[83] or with a drone.[84][85][86] On a flat Earth or a significantly large flat segment, it would not be possible to see the Sun again (unless you are near the edge closest to the Sun) due to a much faster moving solar shadow.[8].
Local solar time and time zones
Ancient timekeeping counted "noon" as the time of day when the Sun is highest in the sky, with the rest of the hours of the day measured against that. During the day, apparent solar time can be measured directly with a sundial. In ancient Egypt, the first known sundials divided the day into 12 hours, although because the length of the day changed with the season, the length of the hours also changed. In the Renaissance, sundials appeared that defined the hours as always of the same duration. In the Middle Ages and Western Europe, tower clocks and chiming clocks were used to keep people close to them aware of the local time, although compared to modern times this was less important in a largely agrarian society.
Because the Sun reaches its highest point at different times for different longitudes (about four minutes of time for each degree of east or west longitude difference), the local solar noon in every city is different, except those directly north or south of each other. This means that clocks in different cities could be out of phase with each other by minutes or hours. As clocks became more precise and industrialization made timekeeping more important, cities switched to mean solar time, which ignores minor variations in local solar noon time during the year, due to the elliptical nature of the Earth's orbit and its inclination.
Generally, differences in clock time between cities were not a problem until the advent of train travel in the 19th century, which made travel between distant cities much faster than on foot or horseback, and also required passengers to show up at specific times to meet their needs. desired trains. In the United Kingdom, railways gradually switched to Greenwich Mean Time (established from local time at the Greenwich Observatory in London), followed by public clocks across the country generally forming a single time zone. In the United States, railroads published schedules based on local time, then on that railroad's standard time (usually local time at the railroad's headquarters), and finally on four standard time zones shared among all railroads, where neighboring zones deferred by exactly one hour. At first, railroad time was synchronized with portable chronometers and later with radio and telegraph signals.
San Francisco "San Francisco (California)")[87] is at 122.41°W longitude and Richmond, Virginia "Richmond (Virginia)")[88] is at 77.46°W longitude. Both are located at about 37.6°N latitude (±0.2°). The roughly 45° difference in longitude translates into about 180 minutes, or 3 hours, of time between sunsets in the two cities, for example. San Francisco is in the Pacific time zone and Richmond is in the Eastern time zone, which are three hours apart, so the local clocks in each city show the sun setting at about the same time when using the local time zone. But a phone call from Richmond to San Francisco at dusk will reveal that there are still three hours of daylight left in California.
Analema
The analemma is the curve that is usually approximately a figure of eight (8) or lemniscate that describes the Sun in the sky if it is observed every day of the year at the same time of day (time zone) and from the same observation place. The axial component of the analemma shows the declination "Declination (astronomy)") of the Sun while the transverse component provides information about the equation of time (which is the difference between apparent solar time and mean solar time). Its inclination depends on the location of the observer. In the northern hemisphere, the analemma curve has the widest loop at the bottom. At the Earth's equator, the analemma is on its side. Finally, in the southern hemisphere it is inverted, showing the wider curve at the top. The analemma is consistent with the fact that the Earth is a sphere that rotates on its own inclined axis of rotation and orbits around the Sun. If the Earth's axis of rotation were not inclined, the analemma curve would have an oval shape.[74][89][90].
Sundial
Using an equatorial sundial you can know the time depending on the position of the shadow that the Sun casts. For its correct functioning, the needle or gnomon of the clock is oriented towards the north and aligned with the axis of rotation of the Earth contained in the meridian plane of the place.[91] Its angle is equal to the latitude. So, in Europe the angle is between 40º and 60º while at the Earth's equator it is parallel to the ground (0º) (Fig. 32).[92][93] The shadow is projected onto a dial whose geometry is variable with respect to latitude.[94] This shadow rotates clockwise in the northern hemisphere and counterclockwise in the southern hemisphere. In turn, a dial is geometrically identical but symmetrically inverted in the opposite hemisphere because both hemispheres are geometrically symmetrical. These observations correspond to a spherical Earth.[95].