Saturn glossary, from A to Z
This Saturn glossary defines, from A to Z, the terms used across the site: the vocabulary of planetary science and stargazing, the names of ring and moon features, spaceflight terms, and words from mythology, art and astrology. Each entry links to the page that covers the topic in depth.
A
Albedo
The fraction of incoming light a body reflects. Enceladus, coated in fresh ice, has one of the highest albedos in the solar system, while the leading face of Iapetus is as dark as coal.
Aphelion
The point in an orbit farthest from the Sun: about 1.51 billion km (940 million miles) for Saturn. See Saturn's orbit.
Astronomical unit (AU)
The average Earth–Sun distance, about 149.6 million km (93 million miles). Saturn orbits 9.54 AU from the Sun (distance from Earth).
B
Black Paintings
A group of fourteen murals painted by Goya around 1819–1823 in his house, the Quinta del Sordo, including Saturn Devouring His Son (Black Paintings).
C
Cassini Division
A dark gap about 4,800 km (3,000 miles) wide between the A and B rings, described by Giovanni Domenico Cassini in 1675. It is shaped largely by a resonance with the moon Mimas (Cassini Division).
Co-orbital moons
Moons that share practically the same orbit. Janus and Epimetheus swap places about every four years (Janus and Epimetheus).
Conjunction
The moment when two bodies appear closest together in the sky, or when a planet passes behind the Sun. See conjunctions.
Cronus
The Titan of Greek myth, father of Zeus, who swallowed his children; the Romans identified him with Saturn. See Saturn and Cronus.
Cryovolcanism
Ice volcanism: eruptions of water, vapor or other volatiles instead of molten rock. The geysers of Enceladus are the most spectacular example.
D
Density
Mass per unit volume. Saturn's, 0.687 g/cm³, is the lowest of any planet and less than that of water (would Saturn float?).
E
E ring
A broad, diffuse ring stretching to about 480,000 km from Saturn's center, fed by ice grains from the geysers of Enceladus.
Ecliptic
The Sun's apparent yearly path across the sky. Saturn, like the other planets, never strays more than a few degrees from it.
Encke Gap
A gap about 325 km (200 miles) wide in the A ring, kept open by the small moon Pan.
Equinox
When the Sun crosses the plane of Saturn's equator, and therefore the ring plane. The most recent were in August 2009 and May 2025 (seasons and tilt).
Exosphere
An extremely thin atmosphere whose molecules almost never collide. Cassini detected one containing oxygen and carbon dioxide around Rhea.
F
F-1 engine
The kerosene and liquid-oxygen rocket engine that is the most powerful single-chamber liquid-fueled engine ever flown. Five F-1s powered the first stage of the Saturn V (F-1 engine).
False color
An image in which invisible wavelengths (infrared, ultraviolet) are shown as visible colors to reveal composition or cloud height (real photos of Saturn).
G
Gas giant
A planet made mostly of hydrogen and helium, with no solid surface, like Jupiter and Saturn. See planet Saturn.
Golden Age
In Roman tradition, a mythical era of peace and plenty when Saturn ruled Latium, celebrated notably by Virgil. See the Golden Age.
Grand Finale
The last phase of the Cassini mission: 22 orbits diving between the planet and its rings from April 2017, ending with entry into the atmosphere on September 15, 2017 (Grand Finale).
Great conjunction
The apparent meeting of Jupiter and Saturn, about every 20 years. The last, on December 21, 2020, brought them within 0.1°; the next is on October 31, 2040.
Great White Spot
A giant storm that erupts in Saturn's northern hemisphere roughly once per Saturnian year; the latest began in late 2010 (Saturn storms).
H
Helium rain
The hypothesis that deep inside Saturn helium separates from hydrogen and falls as droplets, releasing heat. It would explain part of the planet's excess energy output (interior).
Hexagon
A six-sided jet stream circling Saturn's north pole, about 29,000 km (18,000 miles) across, discovered in Voyager images (Saturn's hexagon).
Huygens
ESA's probe, carried by Cassini, that landed on Titan on January 14, 2005; also the Dutch astronomer Christiaan Huygens, who discovered Titan (Huygens landing).
I
Irregular moons
Small, distant moons on tilted, eccentric and often retrograde orbits, probably captured. The great majority of Saturn's 274 moons belong to this class (irregular moons).
L
Lucky imaging
A photographic technique that records thousands of very short frames and stacks only the sharpest, to beat atmospheric turbulence (photographing Saturn).
M
Magnetosphere
The region of space dominated by a planet's magnetic field. Saturn's is filled with plasma that comes largely from Enceladus (magnetosphere and auroras).
Magnitude
The scale of celestial brightness, which runs backward: the smaller the number, the brighter the object. Saturn ranges from about +1.2 to -0.5.
Metallic hydrogen
Hydrogen under pressures of millions of bars, where it conducts electricity like a metal. Its presence deep inside Saturn is thought to generate the planet's magnetic field.
N
Node
A point where an orbit crosses a reference plane, usually the ecliptic. The Moon can occult Saturn only when Saturn lies near a node of the lunar orbit (lunar occultations).
O
Oblateness
How much a globe departs from a perfect sphere. Fast-spinning Saturn is the most oblate planet: its polar radius is about 10% smaller than its equatorial radius (size and mass).
Obliquity
The tilt of a planet's spin axis relative to its orbit: 26.73° for Saturn, giving it seasons about 7.4 years long. Also called axial tilt.
Occultation
One body passing in front of and hiding another. The Moon occults Saturn in series; Saturn's rings sometimes occult stars, which lets astronomers measure ring structure.
Opposition
The alignment in which Earth lies between the Sun and Saturn: the planet is visible all night, at its closest and brightest. See opposition dates.
Opposition effect
A sharp brightening of the rings when the Sun lights them from exactly Earth's direction, at opposition, because the particles' shadows are hidden.
P
Perihelion
The point in an orbit closest to the Sun: about 1.35 billion km (840 million miles) for Saturn, which will next pass it in late 2032.
Phoebe ring
A vast, extremely tenuous dust ring discovered in infrared by the Spitzer Space Telescope in 2009 and linked to the moon Phoebe (Phoebe ring).
Plume
A jet of water vapor and ice grains escaping from an icy surface, as at the south pole of Enceladus (Enceladus plumes).
Propeller
A propeller-shaped disturbance carved in the A ring by a small embedded moonlet too small to clear a full gap (shepherd moons).
R
Resonance
A simple ratio between the orbital periods of two bodies (for example 2:1) that amplifies their gravitational tug on each other. Resonances sculpt the gaps and waves in the rings.
Retrograde motion
A planet's apparent westward drift against the stars, lasting about four and a half months each year for Saturn, caused by Earth overtaking it (Saturn retrograde).
Ring-plane crossing
When Earth passes through the plane of the rings, which are then seen edge-on and nearly vanish. The most recent was on March 23, 2025 (disappearing rings).
Ring rain
Ring material falling into Saturn's atmosphere, guided by the magnetic field and gravity, measured by Cassini during the Grand Finale (ring rain).
Ring seismology
The study of waves that Saturn's internal oscillations imprint on the rings. It yielded a day length of 10 h 33 min 38 s and clues about the core (day length). Also called kronoseismology.
Roche limit
The distance within which a planet's tides prevent a loosely bound body from forming or holding together. The main rings lie inside Saturn's Roche limit (age and origin of the rings).
S
Saturn return
In astrology, the moment Saturn comes back to its birth position, around age 29, then around 58–59. See Saturn return.
Saturn V
NASA's Apollo Moon rocket, 110.6 m (363 ft) tall, launched 13 times between 1967 and 1973 (Saturn V).
Saturnalia
The Roman festival of Saturn, beginning on December 17, with banquets, gift-giving and a temporary reversal of social roles (Saturnalia).
Saturnine
Gloomy, brooding or sluggish in temperament, a meaning inherited from humoral medicine and Renaissance thought, which linked Saturn to melancholy (saturnine melancholy).
Saturnism
Lead poisoning. The term comes from alchemy, which associated lead with Saturn (alchemy and lead).
Seeing
The turbulence of Earth's atmosphere that blurs telescopic views. It, more than the telescope, usually limits useful magnification (best telescope for Saturn).
Shepherd moon
A moon whose gravity confines the edges of a narrow ring or a gap, as Prometheus and Pandora do for the F ring (shepherd moons).
Spokes
Dark, radial, short-lived streaks that appear across the B ring, mostly around equinox, probably electrostatic in origin (ring spokes).
Synchronous rotation
When a moon spins once per orbit and so always shows the same face to its planet, as most of Saturn's large moons do. Hyperion is the exception (Hyperion).
Synodic period
The time between two identical configurations as seen from Earth, such as two oppositions: 378 days for Saturn.
T
Tholins
Complex orange-brown organic compounds formed when ultraviolet light acts on methane and nitrogen. They tint the haze of Titan.
Tiger stripes
Four parallel fractures about 130 km (80 miles) long at the south pole of Enceladus, from which the plumes erupt.
Trojan moon
A moon located 60° ahead of or behind a larger moon on the same orbit. Tethys and Dione each have two (Trojan moons).
Z
Zodiac
The band of sky centered on the ecliptic, divided into twelve signs. Western astrology uses the tropical zodiac, tied to the seasons, which has drifted roughly one constellation away from the actual star patterns (Saturn astrology).
Sources
- NASA Science – Saturn
- Gazetteer of Planetary Nomenclature (IAU/USGS)
- ESA – European Space Agency
- Oxford English Dictionary, entries "saturnine" and "saturnism"