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[2] [21] [62] [66] In the Solar System they may be represented by Earth and Venus. [21] Formation of both planets required merging of approximately 10–20 embryos, while an equal number of them were thrown out of the Solar System. [62] Some of the embryos, which originated in the asteroid belt, are thought to have brought water to Earth. [64]
The Solar System travels alone through the Milky Way in a circular orbit approximately 30,000 light years from the Galactic Center. Its speed is about 220 km/s. The period required for the Solar System to complete one revolution around the Galactic Center, the galactic year, is in the range of 220–250 million years. Since its formation, the ...
French philosopher and mathematician René Descartes was the first to propose a model for the origin of the Solar System in his book The World, written from 1629 to 1633.. In his view, the universe was filled with vortices of swirling particles, and both the Sun and planets had condensed from a large vortex that had contracted, which he thought could explain the circular motion of the plane
1750 – Thomas Wright discusses galaxies and the flattened shape of the Milky Way and speculates nebulae as separate. [11] 1755 – Immanuel Kant drawing on Wright's work conjectures that our galaxy is a rotating disk of stars held together by gravity, and that the nebulae are separate such galaxies; he calls them Island Universes.
The Andromeda Galaxy, for instance, was once referred to as the Andromeda Nebula (and spiral galaxies in general as "spiral nebulae") before the true nature of galaxies was confirmed in the early 20th century by Vesto Slipher, Edwin Hubble, and others. Edwin Hubble discovered that most nebulae are associated with stars and illuminated by starlight.
1781 – Charles Messier and his assistant Pierre Méchain publish the first catalogue of 110 nebulae and star clusters, the most prominent deep-sky objects that can easily be observed from Earth's Northern Hemisphere, in order not to be confused with ordinary Solar System's comets.
Many objects may yet be discovered in the Solar System's uncharted regions. [245] The Oort cloud is a theorized spherical shell of up to a trillion icy objects that is thought to be the source for all long-period comets. [246] [247] No direct observation of the Oort cloud is possible with present imaging technology. [248]
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 ...