A planet is a large, rounded astronomical body that is generally required to be in orbit around a star, stellar remnant, or brown dwarf, and is not one itself. The Solar System has eight planets by the most restrictive definition of the term: the terrestrial planets Mercury, Venus, Earth, and Mars, and the giant planets Jupiter, Saturn, Uranus, and Neptune. The best available theory of planet formation is the nebular hypothesis, which posits that an interstellar cloud collapses out of a nebula to create a young protostar orbited by a protoplanetary disk. Planets grow in this disk by the gradual accumulation of material driven by gravity, a process called accretion.
Following the discovery of the planet Neptune in 1846, there was considerable speculation that another planet might exist beyond its orbit. The search began in the mid-19th century and continued at the start of the 20th with Percival Lowell's quest for Planet X. Lowell proposed the Planet X hypothesis to explain apparent discrepancies in the orbits of the giant planets, particularly Uranus and Neptune, speculating that the gravity of a large unseen ninth planet could have perturbed Uranus enough to account for the irregularities.
The Solar System is the gravitationally bound system of the Sun and the objects that orbit it. It was formed about 4.6 billion years ago when a dense region of a molecular cloud collapsed, forming the Sun and a protoplanetary disc. The Sun is a typical star that maintains a balanced equilibrium by the fusion of hydrogen into helium at its core, releasing this energy from its outer photosphere. Astronomers classify it as a G-type main-sequence star.
Charon, or (134340) Pluto I, is the largest of the five known natural satellites of the dwarf planet Pluto. It has a mean radius of 606 km (377 mi). Charon is the sixth-largest known trans-Neptunian object after Pluto, Eris, Haumea, Makemake, and Gonggong. It was discovered in 1978 at the United States Naval Observatory in Washington, D.C., using photographic plates taken at the United States Naval Observatory Flagstaff Station (NOFS).
The River Parrett flows through the counties of Dorset and Somerset in South West England, from its source in the Thorney Mills springs in the hills around Chedington in Dorset. Flowing northwest through Somerset and the Somerset Levels to its mouth at Burnham-on-Sea, into the Bridgwater Bay nature reserve on the Bristol Channel, the Parrett and its tributaries drain an area of 660 square miles (1,700 km2) – about 50 per cent of Somerset's land area, with a population of 300,000.
The Bridgwater and Taunton Canal is a canal in the south-west of England between Bridgwater and Taunton, opened in 1827 and linking the River Tone to the River Parrett. There were a number of abortive schemes to link the Bristol Channel to the English Channel by waterway in the 18th and early 19th centuries. These schemes followed the approximate route eventually taken by the Bridgwater and Taunton Canal, but the canal was instead built as part of a plan to link Bristol to Taunton by waterway.
In astronomy, the barycenter is the center of mass of two or more bodies that orbit one another and is the point about which the bodies orbit. A barycenter is a dynamical point, not a physical object. It is an important concept in fields such as astronomy and astrophysics. The distance from a body's center of mass to the barycenter can be calculated as a two-body problem.
North Petherton is a town and civil parish in Somerset, England, situated on the edge of the eastern foothills of the Quantocks, and close to the edge of the Somerset Levels. The town has a population of 6,730 as of 2014. The parish includes Hamp, Melcombe, Shearston, Woolmersdon and Huntworth.
The River Tone is a river in the English county of Somerset. The river is about 33 kilometres (21 mi) long. Its source is at Beverton Pond near Huish Champflower in the Brendon Hills, and is dammed at Clatworthy Reservoir. The reservoir outfall continues through Taunton and Curry and Hay Moors, which are designated as a Site of Special Scientific Interest. Finally, it flows into the River Parrett at Burrowbridge.
The Chard Canal was a 13.5 miles (21.7 km) tub boat canal in Somerset, England, that ran from the Bridgwater and Taunton Canal at Creech St. Michael, over four aqueducts, through three tunnels and four inclined planes to Chard. It was completed in 1842, was never commercially viable, and closed in 1868. The major engineering features are still clearly visible in the landscape.
Nine Views is an ambiental installation in Zagreb, Croatia which, together with the sculpture Prizemljeno Sunce, comprises a scale model of the Solar System.
The Sweden Solar System is the world's largest permanent scale model of the Solar System. The Sun is represented by the Avicii Arena in Stockholm, the second-largest hemispherical building in the world. The inner planets can also be found in Stockholm but the outer planets are situated northward in other cities along the Baltic Sea. The system was started by Nils Brenning, professor at the Royal Institute of Technology in Stockholm, and Gösta Gahm, professor at the Stockholm University. The model represents the Solar System on the scale of 1:20 000 000, i.e. one metre represents 20,000 km.
The International Astronomical Union (IAU) defined in August 2006 that, in the Solar System, a planet is a celestial body that:
- is in orbit around the Sun,
- has sufficient mass to assume hydrostatic equilibrium, and
- has "cleared the neighbourhood" around its orbit.
The Westport Canal was built in the late 1830s to link Westport and Langport in Somerset, England. It was part of a larger scheme involving improvements to the River Parrett above Burrow Bridge. Langport is the point at which the River Yeo joins the River Parrett and the intention was to enable trade via the port at Bridgwater. It remained in use until the 1870s, but closed when the Somerset Drainage Commissioners took over control of the River Parrett. Despite a petition against closure by local people, the Commissioners ruled that navigation of the canal must cease due to their interpretation of the Act which gave them control of it, leaving the canal to serve as a drainage channel since 1878.
Retrograde motion in astronomy is, in general, orbital or rotational motion of an object in the direction opposite the rotation of its primary, that is, the central object. It may also describe other motions such as precession or nutation of an object's rotational axis. Prograde or direct motion is more normal motion in the same direction as the primary rotates. However, "retrograde" and "prograde" can also refer to an object other than the primary if so described. The direction of rotation is determined by an inertial frame of reference, such as distant fixed stars.
The Port of Bridgwater is a port, originally located in the town of Bridgwater, Somerset, England. Created under the Bridgwater Navigation and Quays Act 1845 it extends from Brean Down to Hinkley Point in Bridgwater Bay, and parts of the rivers Parrett, River Brue and River Axe. Although no ships now dock in the town, in 2001 103,613 (metric) tonnes of cargo were handled within the area of the Port Authority, most of which were stone products through the wharf at Dunball.
The Sciencenter's Sagan Planet Walk is a walkable scale model of the Solar System, located in Ithaca, New York. The model scales the entire Solar System—both planet size and distances between them—down to one five billionth of its actual size. The exhibition was originally created in 1997 in memory of Ithaca resident and Cornell Professor Carl Sagan.
The following outline is provided as an overview of and topical guide to the Solar System:
The Pajamäki Solar System Scale Model is a scale model of the Solar System built in Helsinki and partly in Espoo, Finland in 1992. Its scale is 1:1 000 000 000, i.e. one to one billion, so that 1 millimeter in the model corresponds to 1 000 kilometers in the actual Solar System. The coordinates given for the model are those for the Sun in Patterinmäki.
The Sun
Mercury
Venus
Earth (and Moon)
Mars
Jupiter
Saturn
Uranus
Neptune
Pluto
