Flat Earth Theory

The horizon or skyline is the apparent line that separates earth from sky, the line that divides all visible directions into two categories: those that intersect the Earth's surface, and those that do not. The true horizon is actually a theoretical line, which can only be observed when it lies on the sea surface. At many locations, this line is obscured by land, trees, buildings, mountains, etc., and the resulting intersection of earth and sky is called the visible horizon. When looking at a sea from a shore, the part of the sea closest to the horizon is called the offing.

Horizon.

The true horizon is horizontal. It surrounds the observer and it is typically assumed to be a circle, drawn on the surface of a perfectly spherical model of the Earth. Its center is below the observer and below sea level. Its distance from the observer varies from day to day due to atmospheric refraction, which is greatly affected by weather conditions. Also, the higher the observer's eyes are from sea level, the farther away the horizon is from the observer. For instance, in standard atmospheric conditions, for an observer with eye level above sea level by 1.70 metres (5 ft 7 in), the horizon is at a distance of about 5 kilometres (3.1 mi).

In many contexts, especially perspective drawing, the curvature of the Earth is disregarded and the horizon is considered the theoretical line to which points on any horizontal plane converge (when projected onto the picture plane) as their distance from the observer increases. For observers near sea level the difference between this geometrical horizon (which assumes a perfectly flat, infinite ground plane) and the true horizon (which assumes a spherical Earth surface) is imperceptible to the unaided eye^{[dubious – discuss]} (but for someone on a 1000-meter hill looking out to sea the true horizon will be about a degree below a horizontal line).

The fundamental plane in a spherical coordinate system is a plane of reference that divides the sphere into two hemispheres. The latitude of a point is then the angle between the fundamental plane and the line joining the point to the centre of the sphere.

The horizontal coordinate system, also known as topocentric coordinate system, is a celestial coordinate system that uses the observer's local horizon as the fundamental plane. Coordinates of an object in the sky are expressed in terms of altitude (or elevation) angle and azimuth...(The azimuth is the angle formed between a reference direction (in this example north) and a line from the observer to a point of interest projected on the same plane as the reference direction orthogonal to the zenith.)


The curvature of the horizon is "easily" seen in this 2008 photograph, taken from a Space Shuttle at an altitude of 226 km (140 mi).

Geometrical horizon distance


Graphs of distances to the true horizon on Earth for a given height h. s is along the surface of the Earth, d is the straight line distance, and ~d is the approximate straight line distance assuming h << the radius of the Earth, 6371 km.

The Kármán line lies within the lower thermosphere (not to scale)

The Kármán line is an attempt to define a boundary between Earth's atmosphere and outer space.This is important for legal and regulatory measures; aircraft and spacecraft fall under different jurisdictions and are subject to different treaties.

Von Kármán at the Caltech Jet Propulsion Laboratory in 1950

The line is named after Theodore von Kármán (1881–1963), a Hungarian American engineerand physicist, who was active primarily in aeronautics and astronautics. He was the first person to calculate the altitude at which the atmosphere becomes too thin to support aeronautical flight and arrived at 83.6 km (51.9 miles) himself.

The Fédération aéronautique internationale ...founded on 14 October 1905, and is headquartered in Lausanne, Switzerland.

The Fédération Aéronautique Internationale (FAI; English: World Air Sports Federation), an international standard-setting and record-keeping body for aeronautics and astronautics, defines the Kármán line as the altitude of 100 kilometres (62 miles; 330,000 feet) above Earth's mean sea level. Other organizations do not use this definition. For instance, the US Air Force and NASA define the limit to be 50 miles (80 km) above sea level for purposes of awarding personnel with outer space badges.

Mappa Mundi, Babylonian “map of the world”

A Mesopotamian cosmology, about two dozen centuries ago

Biblical cosmology

The Astronomer, 1668, by Johannes Vermeer

Guy Consolmagno Vatican Observatory, analyzing a meteorite, 2014

Emily Lakdawalla at the Planetary Conference 2013

The primary mirror assembly of James Webb Space Telescope under construction. This is a segmented mirror and its coated with Gold to reflect (orange-red) visible light, through near-infrared to the mid-infrared

Andromeda Galaxy

Timeline of the universe. A representation of the evolution of the universe over 13.77 billion years. The far left depicts the earliest moment we can now probe, when a period of "inflation" produced a burst of exponential growth in the universe. (Size is depicted by the vertical extent of the grid in this graphic.) For the next several billion years, the expansion of the universe gradually slowed down as the matter in the universe pulled on itself via gravity. More recently, the expansion has begun to speed up again as the repulsive effects of dark energy have come to dominate the expansion of the universe. The afterglow light seen by WMAP was emitted about 375,000 years after inflation and has traversed the universe largely unimpeded since then.

Detail of Raphael's painting The School of Athens, 1510–1511. This could be a representation of Anaximander leaning towards Pythagoras on his left.
...often called the "Father of Cosmology" and founder of astronomy.
...born in the third year of the 42nd Olympiad (610 BC)
Anaximander ( c. 610 – c. 546 BC), belonged to the Milesian school and learned the teachings of his master Thales, father of philosophy. He succeeded Thales and became the second master of that school where he counted  Pythagoras amongst his pupils.

In the Nuremberg Chronicles.
The first "scientist"... he is the first philosopher known to have written down his studies.
The greek miracle reffers to the emergence of what are considered the first philosophers. This movement is seen as a miricale from mythical thought of divine power to a more rational approach. Although it is contested this event apeared to be localised in Greece and was not seen anywhere else prior in the world and is so called the Greek miricale. Anaximander claimed that the cosmic order is not monarchic but geometric, and that this causes the equilibrium of the earth, which is lying in the centre of the universe. 

Third century AD, showing the Pre-Socratic Greek philosopher Anaximander of Miletus holding a sundial...said to have invented the gnomon.

 gnōmōn, literally: "one that knows or examines" is the part of a sundial that casts a  shadow.
...first to mark the solstices and equinoxes on sundials.

Thales of Miletus claimed that the first principle of all things is water. Anaximander noted that water could not be the arche, because it could not give rise to its opposite, fire. Anaximander claimed that none of the elements (earth, fire, air, water) could be arche for the same reason. Instead, he proposed the existence of the apeiron, an indefinite substance from which all things are born and to which all things will return. Apeiron (endless or boundless) is something completely indefinite. The arche is technically what underlies all of reality/appearances.
In the mythical Greek cosmogony of Hesiod (8th to 7th century BC) the first primordial god is Chaos, which is a void or gap.
 Thales believed that the origin or first principle was water. 
The Babylonian cosmology Enuma Elish describes the earliest stage of the universe as one of watery chaos and something similar is described in Genesis.
 ...the transition from chaos to apeiron: "The upper limit of earth borders on air. The lower limit reaches down to the unlimited. (i.e. the Apeiron)"... apeiron meant the "spatial indefinite" 
[Space!]...notion of temporal infinity.
Anaximander explains how the four elements of ancient physics (air, earth, water and fire) are formed, and how Earth and terrestrial beings are formed through their interactions.
According to him, the Universe originates in the separation of opposites in the primordial matter. It embraces the opposites of hot and cold, wet and dry, and directs the movement of things.

Anaximander's bold use of non-mythological explanatory hypotheses...an early effort to demystify physical processes. 

Map of Anaximander's universe
 In his model, the Earth floats very still in the centre of the infinite, not supported by anything. It remains "in the same place because of its indifference".
Its curious shape is that of a cylinder with a height one-third of its diameter. The flat top forms the inhabited world, which is surrounded by a circular oceanic mass.
Anaximander's realization that the Earth floats free without falling... the first cosmological revolution and the starting point of scientific thinking.


Anaximander’s model of the Universe. The Sun, the Moon and each of the stars is actually a transparent ring – or hoop – made of air. Each ring is filled with fire which we can only see when the hole in that particular ring passes over us.

Invented the idea of orbits and "space" itself.


Anaximander's Cylindrical Earth
Anaximander was the first astronomer to consider the Sun as a huge mass, and consequently, to realize how far from Earth it might be, and the first to present a system where the celestial bodies turned at different distances. He built a celestial sphere; this invention undoubtedly made him the first to realize the obliquity of the Zodiac...he must have observed the inclination of the celestial sphere in relation to the plane of the Earth to explain the seasons. 
He was the first "metaphysicist" or theoretical physicist.



Ancient Greek astronomer Hipparchus with the astrolabe he invented. A 16th century engraving.