611 articles
Differential rotation
Differential rotation is when different latitudes of a gaseous body rotate at different speeds, seen in the Sun, where the equator spins in 25 days and the poles in 36.
Dione (moon)
Dione is the fourth-largest moon of Saturn, an icy satellite about 1,123 km across that orbits every 2.7 days and is known for its bright wispy terrain.
Discovery and exploration of the Solar System
The discovery and exploration of the Solar System spans naked-eye antiquity, telescopic finds like Uranus in 1781 and Neptune in 1846, and spacecraft that have reached every planet since 1962.
Discovery of Neptune
The discovery of Neptune was the finding of the eighth planet on 23 September 1846, when Galle and d'Arrest located it near the position Le Verrier predicted from Uranus's orbit.
Discovery Program
The Discovery Program is a NASA planetary science program, created in 1992, funding competitively selected, principal-investigator-led missions like Pathfinder, Kepler, and InSight under a fixed cost cap.
Domicile (astrology)
In astrology, domicile is the placement of a planet in the zodiac sign it rules, such as Mars in Aries; traditionally the highest of the essential dignities.
Double planet
A double planet, also called a binary planet, is a pair of planet-sized bodies orbiting a shared barycenter outside the larger body, with no confirmed example known.
Draconids
The Draconids, historically called the Giacobinids, are an annual meteor shower from comet 21P/Giacobini-Zinner, peaking around October 8 and best viewed in the evening from Draco.
Dusk
Dusk is the darker part of evening twilight, after sunset. In technical use it has three stages, civil, nautical, and astronomical dusk, defined by the Sun's depth below the horizon.
Dwarf planet
A dwarf planet is a celestial body that orbits the Sun, is nearly round, and has not cleared its orbital neighborhood, a category created in 2006.
Dynamical lifetimes and stability of small Solar System bodies
The dynamical lifetime of a small Solar System body is how long it stays in a given orbital region before ejection, collision, or transfer to another class.
Dysnomia (moon)
Dysnomia is the only known moon of the dwarf planet Eris, discovered in 2005 and named for the Greek goddess of lawlessness, daughter of Eris.
E Ring
The E Ring is the outermost of Saturn's named rings, a faint, diffuse band of water-ice grains continuously supplied by the geysers of the moon Enceladus.
Earth
Earth is the third planet from the Sun and the largest of the four terrestrial planets, a 4.54-billion-year-old rocky world with one moon, large surface oceans, and the only known life.
Earth Similarity Index
The Earth Similarity Index (ESI) is a numerical scale from 0 to 1 comparing a planet's physical properties with Earth's, introduced in 2011 to screen exoplanets.
Earth's orbit
Earth's orbit, also called the Earth revolution, is the nearly circular path Earth travels around the Sun every 365.256 days at a mean distance of 149.598 million kilometers.
Eclipse chasing
Eclipse chasing, also called umbraphilia, is traveling to the narrow path of totality of a solar eclipse, which crosses any given spot on Earth only about every 375 years.
Eclipse of Thales
The Eclipse of Thales, also called the Battle of the Eclipse, is the total solar eclipse of 28 May 585 BCE that interrupted a battle between the Lydians and the Medes.
Eclipses used for scientific discovery
Eclipses used for scientific discovery are solar and lunar eclipses exploited as natural experiments, most famously for observing the Sun's corona and testing general relativity in 1919.
Ecliptic
The ecliptic is the plane of Earth's orbit around the Sun, seen from Earth as the great circle the Sun follows yearly, tilted 23.4° to the celestial equator.
Ecliptic coordinate system
The ecliptic coordinate system specifies positions on the celestial sphere by ecliptic longitude and latitude, measured from the ecliptic plane of Earth's orbit, and is widely used for solar system science.
Effective temperature
Effective temperature is the temperature at which a blackbody would radiate the same total power as a source; Earth's is 254.0 K against a surface mean of 15°C.
Eirene (moon)
Eirene, officially Jupiter LVII and once designated S/2003 J 5, is a small retrograde irregular moon of Jupiter in the Carme group, discovered by Scott S. Sheppard in 2003.
Eisinga Planetarium in Franeker
The Eisinga Planetarium, officially the Royal Eise Eisinga Planetarium, is a working scale model of the solar system built into a Franeker home between 1774 and 1781.
Emily Calandrelli
Emily Dawn Calandrelli, known as "The Space Gal," is an American engineer and TV host who became the 100th woman in space on Blue Origin's New Shepard in 2024.
Enceladus
Enceladus is an icy moon of Saturn, about 310 miles across, that vents water vapor and ice into space from a global ocean beneath its ice shell.
Ephemeris
An ephemeris (plural: ephemerides), also called astronomical tables, is a table of computed positions and velocities of an orbiting body, such as a planet, asteroid, or spacecraft, at specific times.
Epimetheus (moon)
Epimetheus is a small, cratered moon of Saturn, about 116 km across, that shares its orbit with Janus; the two swap places roughly every four years.
Epoch (astronomy)
In astronomy, an epoch is a specific instant chosen as a reference for measurements or coordinate systems, since star positions and orbits change over time.
Equilibrium temperature
The equilibrium temperature of a planet is the temperature at which absorbed stellar power equals emitted thermal power, set by stellar luminosity, orbital distance, and albedo.