Celestial Sphere

Borrowed from antiquity, a cornerstone to astronomy is the celestial sphere, which describes that the celestial bodies are projected to a sphere or dome around the observer. Astronomers use a spherical coordinate system to describe the sky. Indeed, a spherical celestial sky is often put forward as evidence for a spherical world.

Going much further than it being a mere representation of a universe spread out around us, astronomers also explain that straight lines in space will appear to us as curves -- as great circles on the celestial sphere. The Moon Tilt Illusion, in which the illuminated portion of the Moon often and paradoxically points upwards and away from the Sun, is attributed as an effect caused by the Sun and Moon resting at different angles upon the celestial sphere. The Milky Way, usually thought of as a flat entity viewed from the side, appears as a bending arch in the sky on the celestial sphere. The Sun's path bends and warps on the celestial sphere. So too do shooting stars, meteors, and the aurora curve upon the celestial sphere above us. We are told, essentially, that we observe the heavens as if we were inside of a planetarium, where straight lines become curved on a spherical surface around us.

Why should it be that a straight line in space is warped and curved? If a straight line was receding in distance from our position, at which point would that straight line become curved? The celestial sphere is proposed by conventional astronomy without a mechanism, and with only vague statements that it is natural to observe nature in this way. Actively ignored as a topic of discussion, only trotted out when forced to explain certain phenomena, the warping of lines upon the celestial sphere showcases the weakness and untenability of conventional astronomy.

In contrast to this, the Flat Earth Theory's celestial model directly provides a mechanism for why lines appear curved in the sky and for our domed observations.

General Astronomy
The book General Astronomy from WikiBooks says:

University of Virginia
An astronomy course at the University of Virginia describes:

New Jersey Institute of Technology
The New Jersey Institute of Technology states:

Princeton University
Professor of Astronomy Charles A.Young, Ph.D, defines spherical astronomy as:

“ Spherical Astronomy — This, discarding all consideration of absolute dimensions and distances, treats the heavenly bodies simply as objects moving on the “surface of the celestial sphere”: it has to do only with angles and directions, and, strictly regarded, is in fact merely Spherical Trigonometry applied to Astronomy. ”

On the Evolution of the Heavenly Spheres
A doctoral thesis explains that the the transformation of straight lines into curves on the celestial sphere has been known since antiquity.

On the Evolution of the Heavenly Spheres An Enactive Approach to Cosmography by David McConville

Full Text Link (Archive)

p.40



Footnotes:


 * 15 Kim Veltman (2004, p. 15) reviews the debate concerning the degree to which Euclid’s Optics was a precursor to either linear or spherical perspective in Literature on Perspective: Sources and Literature of Perspective.


 * 16 Kepler writes, "But our vision has no surface like that of a painting on which it may look at the picture of the hemisphere but only that surface of the sky above in which it sees comets, and it imagines a sphere by the natural instinct of vision. But if a picture of things is extended in straight lines into a concave sphere, and if our vision is in the center of this, the traces of those things will not be straight lines, but, by Hercules, curved ones" (Galilei, Drake, & O’Malley, 1960, pp. 354–355)


 * 17 James Elkins (1988, 1994) summarizes the dispute surrounding da Vinci’s position on the curvature of vision in “Did Leonardo develop a theory of curvilinear perspective?” and The Poetics of Perspective.


 * 18 Hershel (1869) writes, "In celestial perspective, every point to which the view is for the moment directed, is equally entitled to be considered as the "centre of the picture," every portion of the surface of the sphere being similarly related to the eye. Moreover, every straight line (supposed to be indefinitely prolonged) is projected into a semicircle of the sphere, that, namely, in which a plane passing through the line and the eye cuts its surface. And every system of parallel straight lines, in whatever direction, is projected into a system of semicircles of the sphere, meeting in two common apexes, or vanishing points, diametrically opposite to each other, one of which corresponds to the vanishing point of parallels in ordinary perspective; the other, in such perspective has no existence” (p.70)

Sun Path Warped
According to the conventional model the sun's path is a plane which intersects the observer's sky.

A Weber State University astronomy course by Dr. Daniel V. Schroeder (bio) shows the Sun's path is warped upon the celestial dome:

https://physics.weber.edu/schroeder/ua/sunandseasons.html



Caption:

The above website explains the distortion as caused by 'stretching the domed sky onto a flat semicircle' -- as if there is a domed sky around us which modifies the position of the Sun. The diagram comes from the linked Sky Motion Applet.

Dr. Schroeder also provides the following multiple-exposure photo:



Moon and Venus Star Trails
Like the Sun on the celestial dome, Venus and the Moon can also be seen to follow the path of the stars.



"Crescent Moon Venus and star trails at Nagano, Norikura mountain" (Source)

Milky Way Arch
As with the ecliptic, the Milky Way is thought to be a straight entity which we are viewing from the side. It has been asserted that the Milky Way is seen as an arch in the sky.

Source: Matt Rohlader Photography | Caption: "The arch of the Milky Way as seen from Split Rock Lighthouse State Park near Two Harbors, MN."

A Google Image Search for 'Milky Way Arch' will provide many images of the Milky Way arching in the sky.

Photographs of the Milky Way Arch from Google Image Search have been described as being affected by wide-angle, fish-eye, panorama, or other effects. While true that many images of the Milky Way Arch are affected by such distortion, sources tell us that the arch can be seen with the naked eye as well. Astronomer and Associate Editor Alison Klesman, Ph.D. (bio), at Astronomy Magazine informs us that both the Milky Way and the ecliptic (the planar path of the Sun) project as a great circle onto the celestial sphere, which create straight lines overhead, and at lower altitudes create arcs in the sky which are visible to the naked eye:

http://www.astronomy.com/magazine/ask-astro/2018/09/seeing-a-curved-milky-way

Meteors
The International Meteor Organization says:

http://www.internetsv.info/MeteorRC.html

Aurora
Astronomer and mathematician Simon Newcomb (bio) tells us in his Popular Astronomy that the aurora, too, projects upon the celestial sphere:

p.309