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Because the observable universe is defined as that region of the Universe visible to terrestrial observers, Earth is, because of the constancy of the speed of light, the center of Earth's observable universe. Reference can be made to the Earth's position with respect to specific structures, which exist at various scales. It is still ...
380 Earth radii (very inaccurate, true=16000 Earth radii) Aristarchus of Samos made a measurement of the distance of the Sun from the Earth in relation to the distance of the Moon from the Earth. The distance to the Moon was described in Earth radii (20, also inaccurate). The diameter of the Earth had been calculated previously.
The observable universe is a spherical region of the universe consisting of all matter that can be observed from Earth or its space-based telescopes and exploratory probes at the present time; the electromagnetic radiation from these objects has had time to reach the Solar System and Earth since the beginning of the cosmological expansion.
A Counter-Earth or Antichthon (Greek: Ἀντίχθων) was hypothesized by the pre-Socratic Greek philosopher Philolaus (c. 470 – c. 385 BC) to support his non-geocentric cosmology, in which all objects in the universe revolve around a "Central Fire" (unseen from Earth and distinct from the Sun which also revolves around it).
Earth's location in the Universe. Universe – all of time and space and its contents.. Observable universe – spherical region of the Universe comprising all matter that may be observed from Earth at the present time, because light and other signals from these objects have had time to reach Earth since the beginning of the cosmological expansion.
Ptolemy argued that the Earth was a sphere in the center of the universe, from the simple observation that half the stars were above the horizon and half were below the horizon at any time (stars on rotating stellar sphere), and the assumption that the stars were all at some modest distance from the center of the universe. If the Earth were ...
In this system the revolution of the earth around the fire "at the centre" or "the fire of the hearth" (Central Fire) was not yearly, but daily, while the moon's revolution was monthly, and the sun's yearly. It was postulated that the earth's speedy travel past the slower moving sun resulted in the appearance on earth of the sun rising and setting.
The Cosmic Calendar is a method to visualize the chronology of the universe, scaling its currently understood age of 13.8 billion years to a single year in order to help intuit it for pedagogical purposes in science education or popular science.