Planetary system

planetary systemssolar systemssystem
Harley, November 20, 2018 Other, as yet unobserved, orbital possibilities include: double planets; various co-orbital planets such as quasi-satellites, trojans and exchange orbits; and interlocking orbits maintained by precessing orbital planes. Free-floating planets in open clusters have similar velocities to the stars and so can be recaptured. They are typically captured into wide orbits between 100 and 10 5 AU. The capture efficiency decreases with increasing cluster size, and for a given cluster size it increases with the host/primary mass. It is almost independent of the planetary mass.

Moons of Saturn

moon of Saturnmoonmoons
Saturn's satellite system is very lopsided: one moon, Titan, comprises more than 96% of the mass in orbit around the planet. The six other planemo (ellipsoidal) moons constitute roughly 4% of the mass, and the remaining 55 small moons, together with the rings, comprise only 0.04%. Although the boundaries may be somewhat vague, Saturn's moons can be divided into ten groups according to their orbital characteristics. Many of them, such as Pan and Daphnis, orbit within Saturn's ring system and have orbital periods only slightly longer than the planet's rotation period.

Small Solar System body

small Solar System bodiessmall bodiesmacroscopic system
A small Solar System body (SSSB) is an object in the Solar System that is neither a planet, a dwarf planet, nor a natural satellite. The term was first defined in 2006 by the International Astronomical Union (IAU) as follows: "All other objects, except satellites, orbiting the Sun shall be referred to collectively as 'Small Solar System Bodies' ". This encompasses all comets and all minor planets other than those that are dwarf planets.


Ibn SinaIbn SīnāAbu Ali ibn Sina
He believed that each planet had some influence on the earth, but argued against astrologers being able to determine the exact effects. Avicenna's astronomical writings had some influence on later writers, although in general his work could be considered less developed than Alhazen or Al-Biruni. One important feature of his writing is that he considers mathematical astronomy as a separate discipline to astrology. He criticized Aristotle's view of the stars receiving their light from the Sun, stating that the stars are self-luminous, and believed that the planets are also self-luminous. He claimed to have observed Venus as a spot on the Sun.

Rings of Saturn

Cassini DivisionA Ringrings
This ring lies in the plane of Saturn's orbit, or roughly the ecliptic, and thus is tilted 27 degrees from Saturn's equatorial plane and the other rings. Phoebe is inclined by 5° with respect to Saturn's orbit plane (often written as 175°, due to Phoebe's retrograde orbital motion), and its resulting vertical excursions above and below the ring plane agree closely with the ring's observed thickness of 40 Saturn radii. The existence of the ring was proposed in the 1970s by Steven Soter. The discovery was made by Anne J. Verbiscer and Michael F. Skrutskie (of the University of Virginia) and Douglas P. Hamilton (of the University of Maryland, College Park).

Wuxing (Chinese philosophy)

Five ElementsWu XingFive Phases
Xing of wuxing means moving; a planet is called a 'moving star' in Chinese. Wu Xing originally refers to the five major planets (Jupiter, Saturn, Mercury, Mars, Venus) that create five dimensions of earth life. Wuxing is also widely translated as "Five Elements" and this is used extensively by many including practitioners of Five Element acupuncture. This translation arose by false analogy with the Western system of the four elements. Whereas the classical Greek elements were concerned with substances or natural qualities, the Chinese xíng are "primarily concerned with process and change," hence the common translation as "phases" or "agents".

Hellenistic period

HellenisticHellenistic eraHellenistic Age
Also developed in this era was the complex system of astrology, which sought to determine a person's character and future in the movements of the sun, moon, and planets. Astrology was widely associated with the cult of Tyche (luck, fortune), which grew in popularity during this period. The Hellenistic period saw the rise of New Comedy, the only few surviving representative texts being those of Menander (born 342/1 BC). Only one play, Dyskolos, survives in its entirety.


d NêrgalMarsMesopotamian deity of the same name
In the late Babylonian astral-theological system Nergal is related to the planet Mars. As a fiery god of destruction and war, Nergal doubtless seemed an appropriate choice for the red planet, and he was equated by the Greeks to the war-god Ares (Latin Mars)—hence the current name of the planet. In Assyro-Babylonian ecclesiastical art the great lion-headed colossi serving as guardians to the temples and palaces seem to symbolise Nergal, just as the bull-headed colossi probably typify Ninurta. Nergal's chief temple at Cuthah bore the name Meslam, from which the god receives the designation of Meslamtaeda or Meslamtaea, "the one that rises up from Meslam".


planetary embryoproto-planetproto-planets
The exact sequence whereby planetary embryos collided to assemble the planets is not known, but it is thought that initial collisions would have replaced the first "generation" of embryos with a second generation consisting of fewer but larger embryos. These in their turn would have collided to create a third generation of fewer but even larger embryos. Eventually, only a handful of embryos were left, which collided to complete the assembly of the planets proper. Early protoplanets had more radioactive elements, the quantity of which has been reduced over time due to radioactive decay.

Babylonian astronomy

Babylonian astronomersBabylonianastronomer
The oldest surviving planetary astronomical text is the Babylonian Venus tablet of Ammisaduqa, a 7th-century BC copy of a list of observations of the motions of the planet Venus that probably dates as early as the second millennium BC. The Babylonian astrologers also laid the foundations of what would eventually become Western astrology. The Enuma anu enlil, written during the Neo-Assyrian period in the 7th century BC, comprises a list of omens and their relationships with various celestial phenomena including the motions of the planets.

Chemical element

elementelementschemical elements
The abundance of elements in Earth's crust differs from that in the Solar System (as seen in the Sun and heavy planets like Jupiter) mainly in selective loss of the very lightest elements (hydrogen and helium) and also volatile neon, carbon (as hydrocarbons), nitrogen and sulfur, as a result of solar heating in the early formation of the solar system. Oxygen, the most abundant Earth element by mass, is retained on Earth by combination with silicon.


extrasolar planetexoplanetsplanet
The rings of the Solar System's gas giants are aligned with their planet's equator. However, for exoplanets that orbit close to their star, tidal forces from the star would lead to the outermost rings of a planet being aligned with the planet's orbital plane around the star. A planet's innermost rings would still be aligned with the planet's equator so that if the planet has a tilted rotational axis, then the different alignments between the inner and outer rings would create a warped ring system. In December 2013 a candidate exomoon of a rogue planet was announced. On 3 October 2018, evidence suggesting a large exomoon orbiting Kepler-1625b was reported.

Moons of Jupiter

moon of JupiterJovian systemJupiter's moons
Observations suggest that at least the largest member, Amalthea, did not form on its present orbit, but farther from the planet, or that it is a captured Solar System body. These moons, along with a number of as-yet-unseen inner moonlets, replenish and maintain Jupiter's faint ring system. Metis and Adrastea help to maintain Jupiter's main ring, whereas Amalthea and Thebe each maintain their own faint outer rings. They are some of the largest objects in the Solar System outside the Sun and the eight planets in terms of mass and are larger than any known dwarf planet. Ganymede exceeds even the planet Mercury in diameter.

Celestial equator

equatorialequatorial planeequatorial sky
The celestial equator is the great circle of the imaginary celestial sphere on the same plane as the equator of Earth. This plane of reference bases the equatorial coordinate system. In other words, the celestial equator is an abstract projection of the terrestrial equator into outer space. Due to Earth's axial tilt, the celestial equator is currently inclined by about 23.44° with respect to the ecliptic (the plane of Earth's orbit). The inclination has varied from about 22.0° to 24.5° over the past 5 million years. An observer standing on Earth's equator visualizes the celestial equator as a semicircle passing through the zenith, the point directly overhead.


nebulaediffuse nebulanebulosity
Planetary nebulae were given their name by the first astronomical observers who were initially unable to distinguish them from planets, and who tended to confuse them with planets, which were of more interest to them. Our Sun is expected to spawn a planetary nebula about 12 billion years after its formation. A protoplanetary nebula (PPN) is an astronomical object at the short-lived episode during a star's rapid stellar evolution between the late asymptotic giant branch (LAGB) phase and the following planetary nebula (PN) phase. During the AGB phase, the star undergoes mass loss, emitting a circumstellar shell of hydrogen gas. When this phase comes to an end, the star enters the PPN phase.

Rogue planet

free-floating planetsfree-floating planetfree-floating planetary-mass object
A rogue planet (also termed an interstellar planet, nomad planet, free-floating planet, unbound planet, orphan planet, wandering planet, starless planet, or sunless planet) is a planetary-mass object that orbits a galactic center directly. Such objects have been ejected from the planetary system in which they formed or have never been gravitationally bound to any star or brown dwarf. The Milky Way alone may have billions of rogue planets. Some planetary-mass objects may have formed in a similar way to stars, and the International Astronomical Union has proposed that such objects be called sub-brown dwarfs.

Planetary-mass moon

larger moonsSatellite planet
Two moons in the Solar System are larger than the planet Mercury (though less massive): Ganymede and Titan, and seven are larger and more massive than the dwarf planet. The concept of satellite planets – the idea that planetary-mass objects, including planetary-mass moons, are planets – is used by some planetary scientists, such as Alan Stern, who are more concerned with whether a celestial body has planetary geology (that is, whether it is a planetary body) than where it orbits (planetary dynamics). This conceptualization of planets as three classes of objects (classical planets, dwarf planets and satellite planets) has not been accepted by the International Astronomical Union (the IAU).


Hesperosevening starVesper
His name is sometimes conflated with the names for his brother, the personification of the planet as the "morning star" Eosphorus (Greek Ἐωσφόρος, "bearer of dawn") or Phosphorus (Ancient Greek: Φωσφόρος, "bearer of light", often translated as "Lucifer" in Latin), since they are all personifications of the same planet Venus. "Heosphoros" in the Greek Septuagint and "Lucifer" in Jerome's Latin Vulgate were used to translate the Hebrew "Helel" (Venus as the brilliant, bright or shining one), "son of Shahar (Dawn)" in the Hebrew version of Isaiah 14:12.

Moons of Neptune

moon of Neptune14satellite of Neptune
In order of their distance from the planet, the irregular moons are Triton, Nereid, Halimede, Sao, Laomedeia, Psamathe, and Neso, a group that includes both prograde and retrograde objects. The five outermost moons are similar to the irregular moons of other giant planets, and are thought to have been gravitationally captured by Neptune, unlike the regular satellites, which probably formed in situ. Triton and Nereid are unusual irregular satellites and are thus treated separately from the other five irregular Neptunian moons, which are more like the outer irregular satellites of the other outer planets.

PSR B1257+12

PSR 1257+12PSR B1257+12 DLich (pulsar)
Pulsar Planets. PSR 1257+12 on The Extrasolar Planets Encyclopaedia. Lytle, Wayne (1992). "Does This Pulsar Have Orbiting Planets?". Cornell Theory Center.


The name "Phaethon", which means "Shining One", was given also to Phaethon (son of Eos), to one of the horses of Eos (the Dawn), the Sun, the constellation Auriga, and the planet Jupiter, while as an adjective it was used to describe the sun and the moon. In some accounts the planet referred to by this name is not Jupiter but Saturn. In modern times, an asteroid whose orbit brings it close to the sun has been named "3200 Phaethon" after the mythological Phaethon. The French form of the name "Phaethon" is "Phaéton". This form of the word is applied to a kind of carriage and automobile.

Drake equation

Green Bank equationSagan equationDrake's Equation
The Drake equation is: where: N = the number of civilizations in our galaxy with which communication might be possible (i.e. which are on our current past light cone); and R ∗ = the average rate of star formation in our galaxy : f p = the fraction of those stars that have planets : n e = the average number of planets that can potentially support life per star that has planets : f l = the fraction of planets that could support life that actually develop life at some point : f i = the fraction of planets with life that actually go on to develop intelligent life (civilizations) : f c = the fraction of civilizations that develop a technology that releases detectable signs of their existence into

Moons of Uranus

Uranus' natural satellites27Uranian moons
Uranus's irregular moons have elliptical and strongly inclined (mostly retrograde) orbits at large distances from the planet. William Herschel discovered the first two moons, Titania and Oberon, in 1787. The other three ellipsoidal moons were discovered in 1851 by William Lassell (Ariel and Umbriel) and in 1948 by Gerard Kuiper (Miranda). These five have planetary mass, and so would be considered (dwarf) planets if they were in direct orbit about the Sun. The remaining moons were discovered after 1985, either during the Voyager 2 flyby mission or with the aid of advanced Earth-based telescopes.

Orbital period

periodsynodic periodsynodic
Although the plane of the ecliptic is often held fixed at the position it occupied at a specific epoch, the orbital plane of the object still precesses causing the draconitic period to differ from the sidereal period. The anomalistic period is the time that elapses between two passages of an object at its periapsis (in the case of the planets in the Solar System, called the perihelion), the point of its closest approach to the attracting body. It differs from the sidereal period because the object's semi-major axis typically advances slowly.

Rock (geology)

This magma may be derived from partial melts of pre-existing rocks in either a planet's mantle or crust. Typically, the melting of rocks is caused by one or more of three processes: an increase in temperature, a decrease in pressure, or a change in composition. Igneous rocks are divided into two main categories: The chemical abundance and the rate of cooling of magma typically forms a sequence known as Bowen's reaction series. Most major igneous rocks are found along this scale. About 64.7% of the Earth's crust by volume consists of igneous rocks, making it the most plentiful category. Of these, 66% are basalts and gabbros, 16% are granite, and 17% granodiorites and diorites.