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| title | chunk | source | category | tags | date_saved | instance |
|---|---|---|---|---|---|---|
| Glossary of astronomy | 5/20 | https://en.wikipedia.org/wiki/Glossary_of_astronomy | reference | science, encyclopedia | 2026-05-05T07:53:17.709555+00:00 | kb-cron |
detached object Also distant detached object and extended scattered disc object. A dynamical class of minor planet in the outer reaches of the Solar System whose point of closest approach to the Sun is so distant that the object is only moderately or weakly affected by the gravitational influence of Neptune and the other known planets, such that it appears to be "detached" from the rest of the Solar System. Detached objects are thus distinct from other populations of trans-Neptunian objects, such as cubewanos and scattered disc objects.
direct motion See prograde motion.
diurnal motion The apparent motion of an astronomical object (e.g. the Sun, a planet, or a distant star) around the two celestial poles in the Earth's night sky over the course of one day. Diurnal motion is caused by Earth's rotation about its own axis, such that every object appears to follow a circular path called the diurnal circle.
double star Any pair of stars which appear near each other on the celestial sphere, either because the two stars coincidentally lie along nearly the same line of sight from the Earth, though they are in fact physically distant from each other, or because the two stars are actually located in physical proximity to each other, by which they may form a co-moving pair or a binary star system.
dust astronomy
dwarf planet
dwarf star Any star belonging to a category of ordinary main-sequence stars like the Sun, in contrast to evolved giant stars like Betelgeuse and Antares. Confusingly, the term has also come to include stellar remnants known as white dwarfs as well as low-mass substellar objects known as brown dwarfs.
== E ==
early-type star A hotter and more massive star, in contrast to late-type stars that are cooler and less massive. The term originated from historical stellar models that assumed stars began their early life at a high temperature then gradually cooled off as they aged. It may be used to refer to the higher-temperature members of any particular population or category of stars, rather than of all stars in general.
eccentricity See orbital eccentricity.
ecliptic Also ecliptic plane or plane of the ecliptic. The plane defined by the Earth's orbit around the Sun. Hence, the position of the Sun as viewed from the Earth defines the intersection of this plane with the celestial sphere. The ecliptic is widely used as a reference plane for describing the position of other Solar System bodies within various celestial coordinate systems. It differs from the celestial equator because of the axial tilt of the Earth.
ecliptic coordinate system An astronomical coordinate system commonly used to specify the apparent positions, orbits, and axial orientations of objects within the Solar System, with an origin at the geometric center of either the Sun or the Earth, a fundamental plane defined by the plane of Earth's orbit around the Sun (i.e. the plane of the ecliptic), a primary direction towards the vernal equinox, and a right-handed convention. This system is convenient because most of the planets and many small Solar System bodies orbit the Sun with only slight inclinations to the ecliptic. It may be implemented in either spherical or rectangular coordinates.
effective temperature (of a star or planet) The temperature of an ideal black body that would emit the same total energy as electromagnetic radiation.
elliptical galaxy A type of galaxy with an approximately ellipsoidal shape and a smooth, nearly featureless appearance. They are one of three main morphological classes of galaxy, along with spiral and lenticular galaxies.
elliptical orbit Also elliptic orbit. A type of Kepler orbit with an orbital eccentricity of less than 1 (often inclusive of circular orbits, which have eccentricity equal to 0), or one with negative energy. Elliptical orbits take the shape of an ellipse, and are very common in two-body astronomical systems.
elongation The angular separation between the Sun and an orbiting body, such as a planet, as it appears from Earth.
ephemeris A list or table of the expected positions of astronomical objects or artificial satellites in the sky at various dates and times. Modern ephemerides are generally provided by computer software.
epoch A moment in time used as a reference point for some time-varying astronomical quantity, such as the celestial coordinates or orbital elements of an astronomical object, because such quantities are subject to perturbations and change over time. The primary use of astronomical quantities specified by epochs is to calculate other relevant parameters of motion in order to predict future positions and velocities. In modern usage, astronomical quantities are often specified as a polynomial function of a particular time interval, with a given epoch as the temporal point of origin.
equator The imaginary line on a gravitationally rounded spheroid such as a planet that represents the intersection of the spheroid's surface with a plane perpendicular to its axis of rotation and equidistant from its geographical poles. The plane of the Earth's terrestrial equator is the basis for the celestial equator.
equatorial coordinate system An astronomical coordinate system defined by an origin at the geometric center of the Earth, a fundamental plane created by projecting the Earth's terrestrial equator onto the celestial sphere (forming the celestial equator), a primary direction towards the vernal equinox, and a right-handed convention. This system is widely used to specify the positions of celestial objects as viewed from Earth. It may be implemented in either spherical or rectangular coordinates.
equinoctial Of, relating to, or occurring at an equinox.