An Etymological Dictionary of Astronomy and Astrophysics
English-French-Persian

A → European Space Agency (ESA) mission aimed at studying → Mercury, the least explored planet in the inner → Solar System. It was launched on 20 October 2018. Among several goals, BepiColombo will make a complete map of Mercury at different wavelengths. It will chart the planet's → mineralogy and elemental → composition, determine whether the interior of the planet is molten or not, and investigate the extent and origin of Mercury's → magnetic field, the properties of its → magnetosphere, and history of the planet. The trajectory will also be modified by eight planetary flybys: of Earth in April 2020, Venus in 2020 and 2021, and then six times of Mercury itself between 2021 and 2025. BepiColombo will enter Mercury orbit in December 2025. BepiColombo is a joint mission between ESA and the Japanese Aerospace Exploration Agency (JAXA), executed under ESA leadership.

Named after Giuseppe (Bepi) Colombo (1920-1984), a scientist who studied Mercury's orbital motion in detail as well as orbits and interplanetary travel in general.

A catalog of fields along the → ecliptic observed by the → K2 mission. The catalog is hosted at the → Mikulski Archive for Space Telescopes (MAST).

→ ecliptic; → plane; → input; → catalogue.

Prefix meaning "upon, at, close upon (in space or time), on the occasion of, in addition."

Gk. epi- "upon, at, close upon (in space or time), on the occasion of, in addition," cognate with O.Pers./Av. apiy-, aipi- "upon, toward, along; also; however;" Skt. api "also, besides."

Prefix api-, from O.Pers./Av. apiy-, aipi-, as above.

1) In → Ptolemaic system, a circular → orbit of a body around a point that itself orbits circularly another point. Such a system was formulated to explain some → planetary orbits in terms of → circular motions in a → geocentric cosmology.
2a) Math.: A circle that rolls, externally or internally on another circle, generating an → epicycloid or → hypocycloid.
2b) In → galactic dynamics models describing the → spiral arms, a → perturbation of simple circular orbits. → epicyclic theory.

→ epi-; → cycle.

1) Falak-e tadvir, from Ar. falak al-tadwir, from falak "sphere" + tadwir "causing to turn in a circle."
2) → epi-; → cycle.

Of or pertaining to an → epicycle.

→ epicycle; → -ic.

In the → epicyclic theory of Galactic rotation, the frequency at which a star in the → Galactic disk describes an ellipse around its mean circular orbit. The epicyclic frequency relates to the → Oort's constants. In the solar neighborhood the epicyclic frequency is about 32 km s^-1 kpc^-1.

→ epicyclic; → frequency.

In a → disk galaxy, the motion of a star about the orbital → guiding center when it is displaced radially. See also → epicyclic frequency, → epicyclic theory.

→ epicyclic; → oscillation.

The theory that describes the Galactic dynamics, that is the orbits of stars and gas clouds in the → Galactic disk, as well as the spiral → density wave. Formulated by Bertil Lindblad (1895-1965), the epicyclic theory assumes that orbits are circular with small deviations. Star orbits are described by the superposition of two motions: i) a rotation of the star (epicenter) around the Galactic center at the circular angular velocity, Ω, and ii) a retrograde elliptical motion at → epicyclic frequency, κ. The epicyclic motion in the Galactic plane occurs in a retrograde sense to conserve → angular momentum. In general Ω and κ are different and, therefore, orbits do not close. However, seen by an observer who rotates with the epicenter, orbits are closed ellipses.

→ epicyclic; → theory.

A curve traced by a point of a circle that rolls on the outside of a fixed circle. This curve was described by the Gk. mathematicians and astronomer Hipparchus, who made use of it to account for the apparent movement of many of the heavenly bodies.

→ epi-; → cycloid.

The fifth of → Saturn's known satellites. It has a mean radius of 55 x 69 km and orbits its planet at a mean distance of 151,422 km. It shares the same → horseshoe orbit with → Janus. Epimetheus was discovered by Richard L. Walker in 1966. Also known as Saturn XI.

In Gk. mythology, brother of → Prometheus and → Atlas, and husband of → Pandora. His task was to populate the Earth with animals.

A → morphism f : Y → X if, for any two morphisms u,v : X → Z, u f = v f  implies u = v.

→ epi-; → morphism.

1) An incident in the course of a series of events.
2) An incident, scene, etc., within a narrative, usually fully developed and either integrated within the main story or digressing from it (Dictionary.com).

From Fr. épisode from Gk. epeisodion "addition," noun use of neuter of epeisodios "coming in besides," from → epi- "in addition" + eisodos "a coming in, entrance" (from eis"into" + hodos "way," → period).

Apyâ, literally "coming in besides," from api-, → epi-, + â- present stem of âmadan "to come," → rise.

1) Pertaining to or of the nature of an episode.
2) Divided into separate or tenuously related parts or sections.
3) Occurring sporadically or incidentally (Dictionary.com).

→ episode; → -ic.

A branch of philosophy that investigates the possibility, origins, nature, methods, and limits of human knowledge.

From Gk. episteme "knowledge," from Ionic Gk. epistasthai "to understand," literally "overstand," from → epi- "over, near" + histasthai "to stand;" cognate with Pers. istâdan "to stand," → standard; PIE base *sta- "to stand."

From šenaxt, → knowledge, + -šenâsi, → -logy.

A → lens system, also known as an → ocular, used to → magnify the → image formed by the → objective of a → telescope.

→ eye; → piece.

Cašmi "ocular," adj. of cašm→ eye + -i adj. suffix.

A theoretical limit of approximately 6 × 10¹⁹  → electron-volts for the energy of → cosmic rays above which they would lose energy in their interaction with the → cosmic microwave radiation background photons. Cosmic ray protons with these energies produce → pions on blackbody photons via the Δ resonance according to: γ_CMB + p → p + π⁰, or γ_CMB + p → n + π⁺, thereby losing a large fraction of their energy. These interactions would reduce the energy of the cosmic rays to below the GZK limit. Due to this phenomenon, → Ultra-high-energy cosmic rays are absorbed within about 50 Mpc.

Named after Kenneth Greisen (1966), Physical Review Letters 16, 748 and Georgiy Zatsepin & Vadim Kuzmin (1966), Journal of Experimental and Theoretical Physics Letters 4, 78; → limit.

The first achromatic eyepiece consisting of a convex lens and a plano-convex lens. The convex surfaces are turned toward one another.

Named after the inventor Carl Kellner (1826-1855), a German engineer and optician; → eyepiece

A telescopic eyepiece that produces a wide field of view (between 40° and 50°). The eyepiece consists of a single element lens that is normally plano-convex, and a cemented triplet that is usually symmetrical.

→ orthoscopic; → eyepiece.

A solid figure whose six bases are → parallelograms, opposite pairs being identical and parallel.

From Gk. parallelepipedon, from parallelos, → parallel + epipedon "plane surface," from neuter of epipedos "flat," from → epi- + pedon "ground," cognate with L. ped-, pes, → foot.

Parâsuruyé, from parâsu, → parallel, + ruyé, → surface. Lowzivâr, from lowzi, → rhombus + -vâr, → -oid.

An eyepiece consisting of two planoconvex lenses of the same focal length, placed with the convex sides facing each other and with a separation between the lenses of about two-thirds of the focal length of each.

Named after Jesse Ramsden (1735-1800), English maker of astronomical instruments; → eyepiece.