The Crescent Phase

Crescent SaturnThis is a view of Saturn partially lit in crescent phase, a view that can only be seen when the object is between the observer and the Sun. From the Earth, we can only see Mercury and Venus in varying crescent phases and Mars and the other outer planets fully lit. Because the Moon can be either between the Earth and the Sun or farther away, we see it go through all the phases from New to Full to New again.

This picture of Saturn was made by the Cassini spacecraft.

Image Credit: NASA

Pan and Zoom

Pan in the gap
Pan_zoomSaturn’s moon Pan, named for the Greek god of shepherds, rules over quite a different domain—the Encke gap in Saturn’s rings. See the inset at left for a zoomed in view. Pan (28 km across) keeps the Encke gap open through its gravitational influence on the ring particles nearby.

This view looks toward the sunlit side of the rings from about 48 degrees above the ringplane. The image was taken in visible light with the Cassini spacecraft narrow-angle camera on Christmas Day, 2013, from a distance of approximately 2.3 million km from Pan. The image scale is about 14 km) per pixel.

Image Credit: NASA


Helene is a moon of Saturn. In 1988 it was officially named after Helen of Troy, who was the granddaughter of Cronus (Saturn) in Greek mythology. Helene was initially observed from Earth in 1980, and Voyager flybys of Saturn a few years later allowed much closer views. This high resolution image was taken by the Cassini spacecraft in 2011. It’s a small moon with an average diameter of about 36 km.

Image Credit: NASA

A 1979 Saturn

Saturn_Pioneer11The picture above from Pioneer 11 shows Saturn and its moon Titan. When this image was taken in September, 1979, Pioneer was 2,846,000 km from Saturn. This picture was amazing then. Subsequent missions have provided vastly better images.

Pioneer 11 was launched in 1973 to study the asteroid belt, the environment around Jupiter and Saturn, solar winds, and cosmic rays. It’s one of five spacecraft on trajectories that will take them out of the Solar System. Pioneer 11 will pass near the star Lambda Aquila in around four million years.

Image Credit: NASA

A Trio of Moons

moons_SaturnRhea, Enceladus, and Dione are three of Saturn’s moons.  This is what they looked like as seen from the Cassini spacecraft one day in 2011. The night side of Saturn is on the left. Rhea is closest to Cassini. It is the largest moon in center of the image. Enceladus is to the right of Rhea. Dione is partially covered by Saturn.

Image Credit:  NASA

Kissing Moons

Saturn’s two largest moons meet in the sky in a rare apparent embrace. Smog-enshrouded Titan (5,150 km across) glows to the left of  Rhea (1,528 km across).

The image was taken in visible light by the Cassini spacecraft using its narrow-angle camera in 2006. It was about 3.6 million km from Rhea and 5.3 million km from Titan. The moons are in crescent phase.

Image Cedit NASA

A Moon Making Waves

daphnis-wavesDaphnis is one of Saturns small moons that is embedded in the Keeler gap in the ring system. This  image from Cassini shows it kicking up waves as it orbits.

Daphnis is only about 8 km across, but its gravity is powerful enough to disrupt the particles  near the edge of the A ring at the Keeler gap’s edge. Wave-like features form as the moon moves along.

Image Credit: NASA

A Moon Illuminated By Light Reflected From Its Planet

Here’s a picture of a moon shining by the light of its planet. Most of Enceladus in this image is illuminated by sunlight reflected from Saturn. The normally snow-white moon appears in the gold color of Saturn’s cloud tops. Because the light comes from the image left, a labyrinth of ridges throws notable shadows just to the right of the image center; the kilometer-deep canyon Labtayt Sulci is visible just below. The bright crescent on the is the part of Enceladus directly lit by the Sun. This image was taken by the Cassini spacecraft during a close pass by by the moon in 2011. If you look closely at the lower leftt of this digitally sharpened image, you can see plumes of ice crystals thought to originate in a subsurface sea.

Image Credit: NASA

Titan and Rhea

Titan and RheaSaturn’s two largest moons, Titan and Rhea, seem to be stacked together in this true-color picture taken by the Cassini spacecraft. This view looks toward the Saturn-facing side of Rhea. North on Rhea is up and rotated 35 degrees to the right.

Separate images taken with red, green and blue filters using Cassini‘s narrow-angle camera were combined to create this natural-color view. The spacecraft was approximately 1.8 million km away from Rhea and 2.5 million km from Titan.

Image Credit: NASA


Southern WinterWhen this picture was taken in December, 2013, winter was approaching in the southern hemisphere of Saturn, and with that even colder season came a blue hue to some of the planet’s clouds. The color is likely caused by a reduction of ultraviolet sunlight and the haze it produces. With less haze the atmosphere is clearer, increasing Rayleigh scattering (scattering by molecules and smaller particles) and methane absorption. Both processes make the atmosphere appear blue. A similar process cause the blue color of the clouds on Uranus and Neptune.

BTW, it’s now spring in the southern hemisphere of Saturn.

Image Credit: NASA

You Can’t See This From Here

The Cassini spacecraft took this wide-angle view of Saturn on 28 October, 2016, when it was about 1.4 million km from the planet. This point of view is from the far side of the planet showing shadows that can’t be seen from Earth. The spacecraft has spent 13 years exploring Saturn and its moons before being de-orbited into the planet’s atmosphere..

Image Credit: NASA


Dione chasmsSome parts of the surface of Saturn’s moon Dione are covered by linear features, called chasmata, in dramatic contrast to the round impact craters that cover most moons. The bright network of fractures on Dione was seen in poor resolution Voyager images and was called “wispy terrain.” The actual nature of this terrain was unclear until Cassini photos showed we weren’t seeing something like surface deposits of frost but a pattern of bright icy cliffs among myriad fractures. This stress pattern may be related to Dione’s orbital evolution and the effect of tidal stresses over time.

Image Credit: NASA

Sunlight on a Lake

titan_lake_flashTwo bodies in the Solar System have freely flowing liquids on their surface. The Earth has water. Saturn’s largest moon Titan is too cold for liquid water, but it does have liquid methane.

This image shows a flash of sunlight reflected off a lake on Titan. Its northern hemisphere is shrouded in darkness for nearly 15 years, but the sun begins to illuminate the area again as it approaches its spring equinox. The Cassini spacecraft was able to detect the glint at the beginning of Titan’s spring in 2009. The moon’s hazy atmosphere scatters and absorbs many wavelengths of light, including most of the visible spectrum. But an onboard instrument was able to detect the glint in infrared wavelengths that can penetrate through Titan’s atmosphere. This image was created using wavelengths of light in the 5 µm range.

Image Credit: NASA

A Couple of Moons

Dione_MimasBecause of the angle that the Sun’s light is falling on them, Mimas (right) and Dione (left) appear to be staring up at Saturn looming in the background of this image captured by the Cassini spacecraft.

Although certainly large enough to be noticeable, moons like Mimas (396 km across) and Dione (1123 km across) are tiny compared to Saturn (120,700 km across). Even the enormous moon Titan (5,150 kilometers across, larger than the planet Mercury) would be dwarfed by the giant planet in such a picture.

Image Credit: NASA

Titan Over Saturn

The Cassini spacecraft took this picture of Saturn’s Moon Titan looking at the side that always faces away from the planet because the moon’s orbit is tidal locked (like Earth’s Moon’s) Titan is the only moon in the Solar System with a dense atmosphere (visible in this picture), liquid on its surface, and a cycle of evaporation and liquid rain.

Image Credit: NASA

The Storm Around Saturn’s North Pole

Saturn_hurricane1The Cassini spacecraft relayed to Earth thist close-up, visible-light views of a monster hurricane swirling around Saturn’s north pole. It’s 2,000 km wide, 20 times larger than the average hurricane eye on Earth. The clouds at the outer edge of the hurricane are moving at 150 meters per second as the storm swirls inside a large, six-sided weather pattern known as the hexagon. This false-color image highlights the storm at Saturn’s north pole.

Saturn_hurricane3A natural color image is at left.

Hurricanes on Earth feed off warm ocean water, but there is no body of water on Saturn. Learning how these Saturnian storms use water vapor might tell scientists more about how terrestrial hurricanes are generated and sustained. Both terrestrial hurricanes and Saturn’s north polar vortex have a central eye with no clouds or very low clouds. Both have high clouds forming an eye wall, other high clouds spiraling around the eye, and a counter-clockwise spin in the northern hemisphere. But the one on Saturn is much bigger than its counterparts on Earth and spins surprisingly fast. On Saturn, the wind in the eye wall blows more than four times faster than hurricane-force winds on Earth. Terrestrial hurricanes move around, but Saturn’s hurricane is parked over the planet’s north pole. On Earth, hurricanes tend to drift northward because of the forces acting on the winds as the planet rotates. Saturn’s does not drift; it’s already as far north as it can be.

Saturn_hurricane2Scientists believe the massive storm has been churning for years. When Cassini arrived in the Saturn system in 2004, Saturn’s north pole was in winter darkness. Cassini‘s composite infrared spectrometer and visual and infrared mapping spectrometer detected the great vortex, but a visible-light image had to wait for the equinox in 2009 when sunlight begin falling on the higher latitudes of Saturn’s northern hemisphere.

Image Credits: NASA

Saturn on the Radio

Saturn in RadioThis is Saturn, as seen by the Very Large Array (VLA) radio telescope. The bright disk of the planet gradually fades toward the edge, an effect called limb darkening. It’s caused by the gradual cooling moving outward in Saturn’s atmosphere. The rings are seen as emitters of energy outside the planet’s disk, but in front of the planet they absorb the radiation from the bright disk behind and appear as a dark band. That’s in contrast to their appearance in visible light where they reflect the incident sunlight. At radio wavelengths sunlight is much fainter, and we see the actual radio emissions from Saturn.

Image Credit: NRAO


Iapetus is the third-largest satellite of Saturn and the eleventh-largest in the Solar System. Iapetus has a bright hemisphere and a dark hemisphere. Because it is tidally locked, it always keeps the same face towards Saturn. The bright hemisphere is visible from Earth when Iapetus is on the western side of Saturn, and the dark hemisphere is visible when Iapetus is on the eastern side.

This image was pieced together from data taken by the Cassini spacecraft.

Image Cedit: NASA

Ring Shepherds

moons_at_workSaturns rings are divided into distinct bands. The Saturnian moons Prometheus and Pan are both caught “shepherding” their respective rings in this image (click the image to embiggen it). Through their gravitational effect on nearby ring particles, one moon maintains a gap in the outer A ring, and the other helps keep another ring narrowly confined.

Prometheus (86 km across) and its partner Pandora (not seen here), maintains the narrow F ring seen at the bottom left in this image. Pan (28 km across) clears the Encke gap in as it moves along the gap’s center. You may not be able to see Pan unless you embiggen the image. The other bright dot near the inner edge of the Encke gap is a star in the background.

Image Credit: NASA