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The timeline of discovery of Solar System planets and their natural satellites charts the progress of the discovery of new bodies over history. Each object is listed in chronological order of its discovery (multiple dates occur when the moments of imaging, observation, and publication differ), identified through its various designations (including temporary and permanent schemes), and the ...
1619 – Johannes Kepler states his third empirical law of planetary motion, which relates the distance and period of the planetary orbits. [85] 1631 – Pierre Gassendi is the first to observe the transit of Mercury. He was surprised by the small size of the planet compared to the Sun. [86]
At that time, Uranus, Neptune, nor the asteroid belts have been discovered yet. Orbits of planets are drawn to scale, but the orbits of moons and the size of bodies are not. The term "Solar System" entered the English language by 1704, when John Locke used it to refer to the Sun, planets, and comets. [288]
First probe to another planet; Venus flyby (contact lost before flyby) [17] [18] [19] Vostok 1: 12 April 1961 First crewed Earth orbiter (Yuri Gagarin) [20] [21] Ranger 1: 23 August 1961 Attempted lunar test flight (failed to leave Earth orbit) [22] [23] [24] Ranger 2: 18 November 1961 Attempted lunar test flight (failed to leave Earth orbit ...
[56] [60] [61] During this primary depletion period, the effects of the giant planets and planetary embryos left the asteroid belt with a total mass equivalent to less than 1% that of the Earth, composed mainly of small planetesimals. [59] This is still 10–20 times more than the current mass in the main belt, which is now about 0.0005 M E. [62]
The Hindu cosmological time cycles explained in the Surya Siddhanta, give the average length of the sidereal year (the length of the Earth's revolution around the Sun) as 365.2563627 days, which is only 1.4 seconds longer than the modern value of 365.256363004 days. [8]
c. 370,000 years (z=1,100): The "Dark Ages" is the period between decoupling, when the universe first becomes transparent, until the formation of the first stars. Recombination: electrons combine with nuclei to form atoms, mostly hydrogen and helium. At this time, hydrogen and helium transport remains constant as the electron-baryon plasma thins.
All planets orbit the Sun in elliptical orbits (image on the right) and not perfectly circular orbits. [72] The radius vector joining the planet and the Sun has an equal area in equal periods. [73] The square of the period of the planet (one revolution around the Sun) is proportional to the cube of the average distance from the Sun. [74]