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Earth's Rotation
Earth's rotation or Earth's spin is the rotation of planet Earth around its own axis, as well as changes in the orientation of the rotation axis in space. Earth rotates eastward, in prograde motion. As viewed from the northern polar star Polaris, Earth turns counterclockwise. The North Pole, also known as the Geographic North Pole or Terrestrial North Pole, is the point in the Northern Hemisphere where Earth's axis of rotation meets its surface. This point is distinct from Earth's North Magnetic Pole. The South Pole is the other point where Earth's axis of rotation intersects its surface, in Antarctica. Earth rotates once in about 24 hours with respect to the Sun, but once every 23 hours, 56 minutes and 4 seconds with respect to other distant stars ( see below). Earth's rotation is slowing slightly with time; thus, a day was shorter in the past. This is due to the tidal effects the Moon has on Earth's rotation. Atomic clocks show that a modern day is longer by about 1.7 ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Moon
The Moon is Earth's only natural satellite. It is the fifth largest satellite in the Solar System and the largest and most massive relative to its parent planet, with a diameter about one-quarter that of Earth (comparable to the width of Australia). The Moon is a planetary-mass object with a differentiated rocky body, making it a satellite planet under the geophysical definitions of the term and larger than all known dwarf planets of the Solar System. It lacks any significant atmosphere, hydrosphere, or magnetic field. Its surface gravity is about one-sixth of Earth's at , with Jupiter's moon Io being the only satellite in the Solar System known to have a higher surface gravity and density. The Moon orbits Earth at an average distance of , or about 30 times Earth's diameter. Its gravitational influence is the main driver of Earth's tides and very slowly lengthens Earth's day. The Moon's orbit around Earth has a sidereal period of 27.3 days. During each synod ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Heraclides Ponticus
Heraclides Ponticus ( grc-gre, Ἡρακλείδης ὁ Ποντικός ''Herakleides''; c. 390 BC – c. 310 BC) was a Greek philosopher and astronomer who was born in Heraclea Pontica, now Karadeniz Ereğli, Turkey, and migrated to Athens. He is best remembered for proposing that the Earth rotates on its axis, from west to east, once every 24 hours. He is also hailed as the originator of the heliocentric theory, although this is doubted by some. Life Heraclides' father was Euthyphron, a wealthy nobleman who sent his son to study at the Platonic Academy in Athens under its founder Plato and under his successor Speusippus. According to the ''Suda'', Plato, on his departure for Sicily in 361/360 BC, left the Academy in the charge of Heraclides. Heraclides was nearly elected successor to Speusippus as head of the academy in 339/338 BC, but narrowly lost to Xenocrates. Work All of Heraclides' writings have been lost; only a few fragments remain. Like the Pythagoreans Hicetas ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Hicetas
Hicetas ( grc, Ἱκέτας or ; c. 400 – c. 335 BC) was a Greek philosopher of the Pythagorean School. He was born in Syracuse. Like his fellow Pythagorean Ecphantus and the Academic Heraclides Ponticus, he believed that the daily movement of permanent stars was caused by the rotation of the Earth around its axis. When Copernicus referred to ''Nicetus Syracusanus'' (Nicetus of Syracuse) in ''De revolutionibus orbium coelestium'' as having been cited by Cicero as an ancient who also argued that the Earth moved, it is believed that he was actually referring to Hicetas. Cicero refers to Hicetas in the '' Academica,'' volume II, citing in turn Theophrastus Theophrastus (; grc-gre, Θεόφραστος ; c. 371c. 287 BC), a Greek philosopher and the successor to Aristotle in the Peripatetic school. He was a native of Eresos in Lesbos.Gavin Hardy and Laurence Totelin, ''Ancient Botany'', Routle .... According to Heath: :Cicero ays“Hicetas of Syracuse, as Theophrast ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Counter-Earth
The Counter-Earth is a hypothetical body of the Solar System that orbits on the other side of the solar system from Earth. A Counter-Earth or ''Antichthon'' ( el, 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). In modern times a hypothetical planet always on the other side of the Sun from Earth has been called a "Counter-Earth", and has been a recurring theme in UFO claims, as well as in fiction (particularly science fiction). Greek Pythagorean universe An astronomical system positing that the Earth, Moon, Sun, planets and unseen "counter-earth" revolve around an unseen "Central Fire" was developed in the 5th century BC and attributed to the Pythagorean philosopher Philolaus. Philolaus' universe moved "the earth from the center o ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Philolaus
Philolaus (; grc, Φιλόλαος, ''Philólaos''; ) was a Greek Pythagorean and pre-Socratic philosopher. He was born in a Greek colony in Italy and migrated to Greece. Philolaus has been called one of three most prominent figures in the Pythagorean tradition and the most outstanding figure in the Pythagorean school. Pythagoras developed a school of philosophy that was dominated by both mathematics and mysticism. Most of what is known today about the Pythagorean astronomical system is derived from Philolaus's views. He may have been the first to write about Pythagorean doctrine. According to August Böckh (1819), who cites Nicomachus, Philolaus was the successor of Pythagoras. He argued that at the foundation of everything is the part played by the limiting and limitless, which combine in a harmony. With his assertions that the Earth was not the center of the universe (geocentrism), he is credited with the earliest known discussion of concepts in the development of heliocent ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Pythagoreanism
Pythagoreanism originated in the 6th century BC, based on and around the teachings and beliefs held by Pythagoras and his followers, the Pythagoreans. Pythagoras established the first Pythagorean community in the ancient Greek colony of Kroton, in modern Calabria (Italy). Early Pythagorean communities spread throughout Magna Graecia. Pythagoras' death and disputes about his teachings led to the development of two philosophical traditions within Pythagoreanism. The ''akousmatikoi'' were superseded in the 4th century BC as a significant mendicant school of philosophy by the Cynics. The ''mathēmatikoi'' philosophers were absorbed into the Platonic school in the 4th century BC. Following political instability in Magna Graecia, some Pythagorean philosophers fled to mainland Greece while others regrouped in Rhegium. By about 400 BC the majority of Pythagorean philosophers had left Italy. Pythagorean ideas exercised a marked influence on Plato and through him, on all of Western ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Greeks
The Greeks or Hellenes (; el, Έλληνες, ''Éllines'' ) are an ethnic group and nation indigenous to the Eastern Mediterranean and the Black Sea regions, namely Greece, Cyprus, Albania, Italy, Turkey, Egypt, and, to a lesser extent, other countries surrounding the Mediterranean Sea. They also form a significant diaspora (), with Greek communities established around the world.. Greek colonies and communities have been historically established on the shores of the Mediterranean Sea and Black Sea, but the Greek people themselves have always been centered on the Aegean and Ionian seas, where the Greek language has been spoken since the Bronze Age.. Until the early 20th century, Greeks were distributed between the Greek peninsula, the western coast of Asia Minor, the Black Sea coast, Cappadocia in central Anatolia, Egypt, the Balkans, Cyprus, and Constantinople. Many of these regions coincided to a large extent with the borders of the Byzantine Empire of the late 11th ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Earth Rotation (Nepal, Himalayas)
Earth is the third planet from the Sun and the only astronomical object known to harbor life. While large list of largest lakes and seas in the Solar System, volumes of water can be found throughout the Solar System, only water distribution on Earth, Earth sustains liquid surface water. About 71% of Earth's surface is made up of the ocean, dwarfing Earth's polar ice, lakes, and rivers. The remaining 29% of Earth's surface is land, consisting of continents and islands. Earth's surface layer is formed of several slowly moving plate tectonics, tectonic plates, which interact to produce mountain ranges, Volcano, volcanoes, and earthquakes. Earth's liquid outer core generates the magnetic field that shapes the magnetosphere of the Earth, deflecting destructive solar winds. Atmosphere of Earth, The atmosphere of the Earth consists mostly of nitrogen and oxygen. Greenhouse gases in the atmosphere like carbon dioxide (CO2) trap a part of the Solar irradiance, energy from the Sun c ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
8th Century BC
The 8th century BCE started the first day of 800 BC and ended the last day of 701 BC. The 8th century BC is a period of great change for several historically significant civilizations. In Egypt, the 23rd and 24th dynasties lead to rule from Nubia in the 25th Dynasty. The Neo-Assyrian Empire reaches the peak of its power, conquering the Kingdom of Israel as well as nearby countries. Greece colonizes other regions of the Mediterranean Sea and Black Sea. Rome is founded in 753 BC, and the Etruscan civilization expands in Italy. The 8th century BC is conventionally taken as the beginning of Classical Antiquity, with the first Olympiad set at 776 BC, and the epics of Homer dated to between 750 and 650 BC. Iron Age India enters the later Vedic period. Vedic ritual is annotated in many priestly schools in Brahmana commentaries, and the earliest Upanishads mark the beginning of Vedanta philosophy. Events *Late 8th century BC: Earrings, crown and rosettes, from the tomb of ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Day Length Fluctuations
The length of the day (LOD), which has increased over the long term of Earth's history due to tidal effects, is also subject to fluctuations on a shorter scale of time. Exact measurements of time by atomic clocks and satellite laser ranging have revealed that the LOD is subject to a number of different changes. These subtle variations have periods that range from a few weeks to a few years. They are attributed to interactions between the dynamic atmosphere and Earth itself. The International Earth Rotation and Reference Systems Service monitors the changes. In the absence of external torques, the total angular momentum of Earth as a whole system must be constant. Internal torques are due to relative movements and mass redistribution of Earth's core, mantle, crust, oceans, atmosphere, and cryosphere. In order to keep the Conservation of angular momentum, total angular momentum constant, a change of the angular momentum in one region must necessarily be balanced by angular mome ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Leap Second
A leap second is a one- second adjustment that is occasionally applied to Coordinated Universal Time (UTC), to accommodate the difference between precise time ( International Atomic Time (TAI), as measured by atomic clocks) and imprecise observed solar time ( UT1), which varies due to irregularities and long-term slowdown in the Earth's rotation. The UTC time standard, widely used for international timekeeping and as the reference for civil time in most countries, uses TAI and consequently would run ahead of observed solar time unless it is reset to UT1 as needed. The leap second facility exists to provide this adjustment. The leap second was introduced in 1972 and since then 27 leap seconds have been added to UTC. Because the Earth's rotation speed varies in response to climatic and geological events, UTC leap seconds are irregularly spaced and unpredictable. Insertion of each UTC leap second is usually decided about six months in advance by the International Earth Rotati ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
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