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Aristarchus of Samos (/ ˌ æ r ə ˈ s t ɑːr k ə s /; Ancient Greek: Ἀρίσταρχος ὁ Σάμιος, Aristarkhos ho Samios; c. 310 – c. 230 BC) was an ancient Greek astronomer and mathematician who presented the first known heliocentric model that placed the Sun at the center of the universe, with the Earth revolving around the Sun once a year and rotating about its axis once a day.
The movements of the Moon, the planets, and the Sun around the static Earth in the Ptolemaic geocentric model (upper panel) in comparison to the orbits of the planets and the daily-rotating Earth around the Sun in the Copernican heliocentric model (lower panel). In both models, the Moon rotates around the Earth.
By astronomical convention, the four seasons are determined by the solstices (the two points in the Earth's orbit of the maximum tilt of the Earth's axis, toward the Sun or away from the Sun) and the equinoxes (the two points in the Earth's orbit where the Earth's tilted axis and an imaginary line drawn from the Earth to the Sun are exactly ...
Philolaus (4th century BCE) was one of the first to hypothesize movement of the Earth, probably inspired by Pythagoras' theories about a spherical, moving globe. In the 3rd century BCE, Aristarchus of Samos proposed what was, so far as is known, the first serious model of a heliocentric Solar System, having developed some of Heraclides Ponticus' theories (speaking of a "revolution of the Earth ...
A tellurion will show the Earth with the Moon revolving around the Sun. It will use the angle of inclination of the equator from the table above to show how it rotates around its own axis. It will show the Earth's Moon, rotating around the Earth. [23] A lunarium is designed to show the complex motions of the Moon as it revolves around the Earth.
The Sun is part of one of the Milky Way's outer spiral arms, known as the Orion–Cygnus Arm or Local Spur. [270] [271] It is a member of the thin disk population of stars orbiting close to the galactic plane. [272] Its speed around the center of the Milky Way is about 220 km/s, so that it completes one revolution every 240 million years. [269]
Earth's rotation axis moves with respect to the fixed stars (inertial space); the components of this motion are precession and nutation. It also moves with respect to Earth's crust; this is called polar motion. Precession is a rotation of Earth's rotation axis, caused primarily by external torques from the gravity of the Sun, Moon and other bodies.
The Earth's rotation around its axis, and revolution around the Sun, evolve over time due to gravitational interactions with other bodies in the Solar System. The variations are complex, but a few cycles are dominant.