Co-orbital configuration

co-orbitaltrojan moonTrojan planet
The longitude of the periapsis is the sum of the mean longitude and the mean anomaly and the mean longitude is the sum of the longitude of the ascending node and the argument of periapsis. Trojan objects orbit 60° ahead of or behind a more massive object, both in orbit around an even more massive central object. The best known example are the asteroids that orbit ahead of or behind Jupiter around the Sun. Trojan objects do not orbit exactly at one of either Lagrangian points, but do remain relatively close to it, appearing to slowly orbit it. In technical terms, they librate around = (±60°, ±60°).

Planet Nine

ninth planetalternative theoriesgroup of objects
The orbital poles of the objects precess around, or circle, the pole of the Solar System's Laplace plane. At large semi-major axes the Laplace plane is warped toward the plane of Planet Nine's orbit. This causes orbital poles of the eTNOs on average to be tilted toward one side and their longitudes of ascending nodes to be clustered. Planet Nine can deliver eTNOs into orbits roughly perpendicular to the ecliptic. Several objects with high inclinations, greater than 50°, and large semi-major axes, above 250 AU, have been observed. These orbits are produced when some low inclination eTNOs enter a secular resonance with Planet Nine upon reaching low eccentricity orbits.

Orbital plane (astronomy)

orbital planeorbital planesplane of its orbit
The orbital plane of a revolving body is the geometric plane in which its orbit lies. Three non-collinear points in space suffice to determine an orbital plane. A common example would be the positions of the centers of a massive body (host) and of an orbiting celestial body at two different times/points of its orbit. The orbital plane is defined in relation to a reference plane by two parameters: inclination (i) and longitude of the ascending node . By definition, the reference plane for the Solar System is usually considered to be Earth's orbital plane, which defines the ecliptic, the circular path on the celestial sphere that the Sun appears to follow over the course of a year.

Epoch (astronomy)

But the argument of perihelion, longitude of the ascending node and the inclination are all coordinate-dependent, and are specified relative to the reference frame of the equinox and ecliptic of another date "2000.0", otherwise known as J2000, i.e. January 1.5, 2000 (12h on January 1) or JD 2451545.0. In the particular set of coordinates exampled above, much of the elements has been omitted as unknown or undetermined; for example, the element n allows an approximate time-dependence of the element M to be calculated, but the other elements and n itself are treated as constant, which represents a temporary approximation (see Osculating elements).

Equatorial bulge

bulgesbulges slightlybulging
If the reference z axis of the coordinate system adopted is aligned along the Earth's symmetry axis, then only the longitude of the ascending node Ω, the argument of pericenter ω and the mean anomaly M undergo secular precessions. Such perturbations, which were earlier used to map the Earth's gravitational field from space, may play a relevant disturbing role when satellites are used to make tests of general relativity because the much smaller relativistic effects are qualitatively indistinguishable from the oblateness-driven disturbances.

John Couch Adams

AdamsAdams, John CouchJ. C. Adams
Newton had asserted that the longitude of the ascending node, that marked where the shower would occur, was increasing and the problem of explaining this variation attracted some of Europe's leading astronomers. Using a powerful and elaborate analysis, Adams ascertained that this cluster of meteors, which belongs to the Solar System, traverses an elongated ellipse in 33.25 years, and is subject to definite perturbations from the larger planets, Jupiter, Saturn, and Uranus. These results were published in 1867. Some experts consider this Adams's most substantial achievement.

Newton's theorem of revolving orbits

The motion of the Moon can be measured accurately, and is noticeably more complex than that of the planets. The ancient Greek astronomers, Hipparchus and Ptolemy, had noted several periodic variations in the Moon's orbit, such as small oscillations in its orbital eccentricity and the inclination of its orbit to the plane of the ecliptic. These oscillations generally occur on a once-monthly or twice-monthly time-scale. The line of its apses precesses gradually with a period of roughly 8.85 years, while its line of nodes turns a full circle in roughly double that time, 18.6 years. This accounts for the roughly 18-year periodicity of eclipses, the so-called Saros cycle.

VSOP (planets)

Variations Séculaires des Orbites PlanétairesVSOP82 and VSOP87VSOP87
Its precision is of a few 0.1″ for the four planets, i.e. a gain of a factor between 1.5 and 15, depending on the planet, compared to VSOP2013. The precision of the theory of Pluto remains valid up to the time span from 0 to +4000. * a semi-major axis. e eccentricity. i inclination. Ω longitude of the ascending node. ω argument of perihelion (or longitude of perihelion ϖ = ω + Ω). T time of perihelion passage (or mean anomaly M). VSOP87 Heliocentric ecliptic orbital elements for the equinox J2000.0; the 6 orbital elements, ideal to get an idea of how the orbits are changing over time.

List of astronomy acronyms

Astronomical acronymsacronymEGGs
LOAN – Longitude of ascending node. LOFAR – (telescope) LOw Frequency ARray, for radio astronomy. LONEOS – (observing program) Lowell Observatory Near-Earth Object Search. LOSS – (observing program) Lick Observatory Supernova Search. LOTIS – (telescope) Livermore Optical Transient Imaging System, a telescope designed to find the optical counterparts of gamma ray bursts. LOTOSS – (observing program) Lick Observatory and Tenagra Observatory Supernova Searches. LP – (catalog) Luyten Palomar, a catalog of proper motion measurements of stars. LPI – (organization) Lunar and Planetary Institute.

Secular resonance

secularν 6 resonanceresonant alignment
Typically, the synchronized precessions in secular resonances are between the rates of change of the argument of the periapses or the rates of change of the longitude of the ascending nodes of two system bodies. Secular resonances can be used to study the long-term orbital evolution of asteroids and their families within the asteroid belt (see the ν 6 resonance below). Secular resonances occur when the precession of two orbits is synchronised (a precession of the perihelion, with frequency g, or the ascending node, with frequency s, or both).

Longitude of the periapsis

longitude of perihelionlongitude of periastronLongitude of pericenter
For the motion of a planet around the Sun, this position is called longitude of perihelion ϖ, which is the sum of the longitude of the ascending node Ω, and the argument of perihelion ω. The longitude of periapsis is a compound angle, with part of it being measured in the plane of reference and the rest being measured in the plane of the orbit. Likewise, any angle derived from the longitude of periapsis (e.g., mean longitude and true longitude) will also be compound. Sometimes, the term longitude of periapsis is used to refer to ω, the angle between the ascending node and the periapsis. That usage of the term is especially common in discussions of binary stars and exoplanets.

Astronomical object

celestial bodiescelestial bodycelestial object
Examples of astronomical objects include planetary systems, star clusters, nebulae, and galaxies, while asteroids, moons, planets, and stars are astronomical bodies. A comet may be identified as both body and object: It is a body when referring to the frozen nucleus of ice and dust, and an object when describing the entire comet with its diffuse coma and tail. The universe can be viewed as having a hierarchical structure. At the largest scales, the fundamental component of assembly is the galaxy.


gravitationgravitationalgravitational force
The application of Newton's law of gravity has enabled the acquisition of much of the detailed information we have about the planets in the Solar System, the mass of the Sun, and details of quasars; even the existence of dark matter is inferred using Newton's law of gravity. Although we have not traveled to all the planets nor to the Sun, we know their masses. These masses are obtained by applying the laws of gravity to the measured characteristics of the orbit. In space an object maintains its orbit because of the force of gravity acting upon it. Planets orbit stars, stars orbit galactic centers, galaxies orbit a center of mass in clusters, and clusters orbit in superclusters.

Clearing the neighbourhood

cleared the neighborhoodcleared its neighborhoodcleared their neighbourhoods
Below is a list of planets and dwarf planets ranked by Margot's planetary discriminant Π, in decreasing order. For all eight planets defined by the IAU, Π is orders of magnitude greater than 1, whereas for all dwarf planets, Π is orders of magnitude less than 1. Also listed are Stern–Levison's Λ and Soter's µ; again, the planets are orders of magnitude greater than 1 for Λ and 100 for µ, and the dwarf planets are orders of magnitude less than 1 for Λ and 100 for µ. Also shown are the distances where Π = 1 and Λ = 1 (where the body would change from being a planet to being a dwarf planet).

International Astronomical Union

IAUWorking Group for Planetary System NomenclatureInternational Astronomical Union (IAU)
Thirty-two Commissions (referred to initially as Standing Committees) were appointed at the Brussels meeting and focused on topics ranging from relativity to minor planets. The reports of these 32 Commissions formed the main substance of the first General Assembly, which took place in Rome, Italy, 2–10 May 1922. By the end of the first General Assembly, ten additional nations (Australia, Brazil, Czecho-Slovakia, Denmark, the Netherlands, Norway, Poland, Romania, South Africa, and Spain) had joined the Union, bringing the total membership to 19 countries.


134340 Pluto(134340) Plutoescaped moon of Neptune
This means that when Pluto is closest to the Sun, it is at its farthest above the plane of the Solar System, preventing encounters with Neptune. This is a consequence of the Kozai mechanism, which relates the eccentricity of an orbit to its inclination to a larger perturbing body—in this case Neptune. Relative to Neptune, the amplitude of libration is 38°, and so the angular separation of Pluto's perihelion to the orbit of Neptune is always greater than 52° (90°–38°). The closest such angular separation occurs every 10,000 years. Second, the longitudes of ascending nodes of the two bodies—the points where they cross the ecliptic—are in near-resonance with the above libration.


planetesimalsasteroid impactsplanetessimal
Alternatively, planetesimals may form in a very dense layer of dust grains that undergoes a collective gravitational instability in the mid-plane of a protoplanetary disk or via the concentration and gravitational collapse of swarms of larger particles in streaming instabilities. Many planetesimals eventually break apart during violent collisions, as may have happened to 4 Vesta and 90 Antiope, but a few of the largest planetesimals may survive such encounters and continue to grow into protoplanets and later planets.


starsstellarmassive star
To the Ancient Greeks, some "stars", known as planets (Greek πλανήτης (planētēs), meaning "wanderer"), represented various important deities, from which the names of the planets Mercury, Venus, Mars, Jupiter and Saturn were taken. (Uranus and Neptune were also Greek and Roman gods, but neither planet was known in Antiquity because of their low brightness. Their names were assigned by later astronomers.) Circa 1600, the names of the constellations were used to name the stars in the corresponding regions of the sky. The German astronomer Johann Bayer created a series of star maps and applied Greek letters as designations to the stars in each constellation.

Planets in astrology

Astrologers call the seven classical planets "the seven personal and social planets", because they are said to represent the basic human drives of every individual. The personal planets are the Sun, Moon, Mercury, Venus and Mars. The social or transpersonal planets are Jupiter and Saturn. Jupiter and Saturn are often called the first of the "transpersonal" or "transcendent" planets as they represent a transition from the inner personal planets to the outer modern, impersonal planets. The outer modern planets Uranus, Neptune and Pluto are often called the collective or transcendental planets. The following is a list of the planets and their associated characteristics.


volcanicvolcanoesvolcanic igneous activity
The planet Venus has a surface that is 90% basalt, indicating that volcanism played a major role in shaping its surface. The planet may have had a major global resurfacing event about 500 million years ago, from what scientists can tell from the density of impact craters on the surface. Lava flows are widespread and forms of volcanism not present on Earth occur as well. Changes in the planet's atmosphere and observations of lightning have been attributed to ongoing volcanic eruptions, although there is no confirmation of whether or not Venus is still volcanically active.

Terrestrial planet

terrestrial planetsrockyrocky planet
A terrestrial planet, telluric planet, or rocky planet is a planet that is composed primarily of silicate rocks or metals. Within the Solar System, the terrestrial planets are the inner planets closest to the Sun, i.e. Mercury, Venus, Earth, and Mars. The terms "terrestrial planet" and "telluric planet" are derived from Latin words for Earth (Terra and Tellus), as these planets are, in terms of structure, Earth-like. These planets are located between the Sun and the asteroid belt.

Mercury (planet)

MercuryMercurioplanet Mercury
Combined with a 3:2 spin–orbit resonance of the planet's rotation around its axis, it also results in complex variations of the surface temperature. The resonance makes a single solar day on Mercury last exactly two Mercury years, or about 176 Earth days. Mercury's orbit is inclined by 7 degrees to the plane of Earth's orbit (the ecliptic), as shown in the diagram on the right. As a result, transits of Mercury across the face of the Sun can only occur when the planet is crossing the plane of the ecliptic at the time it lies between Earth and the Sun. This occurs about every seven years on average. Mercury's axial tilt is almost zero, with the best measured value as low as 0.027 degrees.

Giant planet

Jovian planetgiant planetsJovian
. * Planet Nine Chthonian planet. Planetary system. Sudarsky's gas giant classification. Terrestrial planet. Tyche (hypothetical planet). Q&A: The IAU's Proposed Planet Definition, 16 August 2006, 2:00 AM ET. BBC News: Q&A New planets proposal Wednesday, 16 August 2006, 13:36 GMT 14:36 UK. Q&A: The IAU's Proposed Planet Definition 16 August 2006 2:00 am ET. BBC News: Q&A New planets proposal Wednesday, 16 August 2006, 13:36 GMT 14:36 UK. Gas Giants in Science Fiction:. Episode "Giants" on The Science Channel TV show Planets.

Deferent and epicycle

epicyclesdeferentdeferents and epicycles
In both Hipparchian and Ptolemaic systems, the planets are assumed to move in a small circle called an epicycle, which in turn moves along a larger circle called a deferent. Both circles rotate clockwise and are roughly parallel to the plane of the Sun's orbit (ecliptic). Despite the fact that the system is considered geocentric, each planet's motion was not centered on the Earth but at a point slightly away from the Earth called the eccentric. The orbits of planets in this system are similar to epitrochoids. In the Hipparchian system the epicycle rotated and revolved along the deferent with uniform motion.


MartianCoordinatesplanet Mars
The days and seasons are likewise comparable to those of Earth, because the rotational period as well as the tilt of the rotational axis relative to the ecliptic plane are very similar. Mars is the site of Olympus Mons, the largest volcano and highest known mountain in the Solar System, and of Valles Marineris, one of the largest canyons in the Solar System. The smooth Borealis basin in the northern hemisphere covers 40% of the planet and may be a giant impact feature. Mars has two moons, Phobos and Deimos, which are small and irregularly shaped. These may be captured asteroids, similar to 5261 Eureka, a Mars trojan.