611 articles
Eris (dwarf planet)
Eris is a dwarf planet in the scattered disk beyond Neptune and the most massive known. Its 2005 discovery led the IAU to reclassify Pluto in 2006.
Ersa
Ersa (Jupiter LXXI, S/2018 J1) is a tiny outer prograde moon of Jupiter discovered by Scott S. Sheppard, announced 2018, named 2019 for the Greek goddess of dew, daughter of Zeus and Selene, sister of Pandia, radius about 1.5 km.
Eunomia family
Eunomia family, an S-type collisional asteroid family at 2.5–2.7 AU in the intermediate main belt, parent body 15 Eunomia (255 km), partially differentiated, olivine-rich, thousands of members.
Europa (moon)
Europa (Jupiter II) is Jupiter's smallest Galilean moon, an icy body about 90 percent the size of Earth's Moon that likely holds a global salty ocean beneath its ice.
Exaltation (astrology)
Exaltation is a traditional astrological concept in which each of the seven classical planets has one zodiac sign of heightened expression, with the opposite sign its fall.
Exeligmos
The exeligmos (Greek ἐξελιγμός) is the triple Saros eclipse cycle, lasting about 54 years and 33 days, after which eclipses recur at nearly the same longitude and local time.
Exoplanet atmosphere
An exoplanet atmosphere is the envelope of gas around a planet orbiting a star other than the Sun, studied by the fingerprints its molecules leave on starlight.
Exoplanet atmospheric chemistry
Exoplanet atmospheric chemistry is the study of chemical composition in atmospheres of planets orbiting other stars, inferred from spectroscopy and models, with detections of water, methane, and carbon dioxide.
Exoplanet magnetic field
An exoplanet magnetic field is the global magnetic field generated inside a planet orbiting a star other than the Sun, first directly detected via radio bursts from Beta Pictoris b in the mid-2020s.
Exosphere
The exosphere, also known as the exoatmosphere, is the outermost layer of a planet's atmosphere, where atoms travel without colliding and the fastest escape into space.
Extreme trans-Neptunian object
An extreme trans-Neptunian object orbits the Sun beyond Neptune with a semimajor axis of roughly 150 au or more, a class tied to the Planet Nine hypothesis.
Fallen Astronaut
Fallen Astronaut is a small aluminum figurine placed on the Moon in 1971 by Apollo 15 commander David Scott, beside a plaque honoring 14 dead astronauts and cosmonauts.
Family Portrait (Voyager)
The Family Portrait (Solar System Family Portrait) is a mosaic of 60 images taken by Voyager 1 in 1990, showing six planets and the Pale Blue Dot.
Fifth Giant
The Fifth Giant, or hypothetical fifth giant planet, is a proposed ice giant ejected into interstellar space by Jupiter during the Solar System's instability phase.
Filament eruption
A filament eruption is the sudden ejection of a solar filament, cool dense plasma held above the Sun by magnetic fields, into space or the solar atmosphere.
Formation and evolution of the Solar System
The Solar System formed about 4.6 billion years ago from the collapse of a giant molecular cloud, with planets accreting from a disk around the young Sun.
Francisco (moon)
Francisco, designated Uranus XXII, is a small, dark retrograde moon of Uranus discovered in 2001, about 22 km across and the innermost of its irregular satellites.
From the Earth to the Moon
From the Earth to the Moon (De la Terre à la Lune) is an 1865 Jules Verne novel in which the Baltimore Gun Club fires a three-man projectile at the Moon from Florida.
Full moon
A full moon is the lunar phase in which the Moon is opposite the Sun, fully lit as seen from Earth, occurring about every 29.5 days.
Future evolution of the Solar System
The future evolution of the Solar System is the projected long-term changes to planetary orbits, including Mercury's roughly 1% instability chance and Earth's contested fate.
Galactic tide
A galactic tide is the differential gravitational field of a galaxy, which torques distant Oort cloud comets and sends long-period comets into the inner Solar System.
Galilean moons
The Galilean moons, also called the Galilean satellites or Medicea Sidera, are Jupiter's four largest moons, Io, Europa, Ganymede, and Callisto, discovered by Galileo Galilei in January 1610 and believed to hold subsurface oceans.
Ganymede (moon)
Ganymede, also known as Jupiter III, is Jupiter's largest moon and the largest in the solar system, discovered by Galileo in 1610, with evidence of a subsurface ocean.
Gas giant
A gas giant, or gas planet, is a large planet composed mostly of hydrogen and helium with no true surface; Jupiter and Saturn are examples.
Geminids
The Geminids are an annual meteor shower, active each December with a peak around December 13–14 and up to about 150 meteors per hour, supplied by asteroid 3200 Phaethon.
Geometric albedo
Geometric albedo is the ratio of a celestial body's brightness at full phase to that of a perfectly reflecting, diffusely scattering disk of the same apparent size.
Gerd (moon)
Gerd (Saturn LVII) is a small, retrograde irregular moon of Saturn's Norse group, about 3.5 kilometers across, first imaged in 2004 and named in 2022.
Giant planet
A giant planet, or Jovian planet, is a massive planet made mainly of gases and fluids with no solid surface, such as Jupiter, Saturn, Uranus, and Neptune.
Giant-impact hypothesis
The giant-impact hypothesis, also called the Big Whack, holds that the Moon formed from debris ejected when a Mars-sized body called Theia struck young Earth roughly 4.5 billion years ago.
Gleissberg cycle
The Gleissberg cycle is an 80- to 100-year modulation of the Sun's 11-year sunspot cycle, named for German astronomer Wolfgang Gleissberg, who described it around 1938.