Immediately Recognizable, Always Unforgettable: Saturn
Saturn is a gas giant planet named after the Roman god of agriculture and harvest. It is the second-largest planet in our solar system, with a diameter about 9 times that of Earth, slightly smaller than Jupiter, which is about 11 times the size of Earth. Saturn is less dense than Jupiter, however, possessing 95 times the mass of Earth, or less than ⅓ of that of Jupiter.
Saturn is so low in density that it would float in water. Jupiter and Saturn are similar in size despite Saturn’s much lower mass because Jupiter’s higher mass causes it to condense under its own gravity, which causes any further mass growth to simply result in more pressure on its interior. Most gas giant planets and red dwarf stars in the Universe are not much bigger than Saturn or Jupiter for this reason, even if they possess several hundred times more mass.
Saturn orbits the Sun at a distance of approximately 890 million miles, or about 9-10 times the distance between the Earth and the Sun, and takes 29 Earth years to complete one orbit. Saturn is the sixth planet from the Sun. From Earth, it is the third planet out, after Mars and Jupiter, the latter of which lies half as far from the Sun as Saturn. Sunlight takes about 90 minutes to reach Saturn, and Saturn’s reflected light takes about 80 minutes to reach us due to its distance.
When it is closest to Earth, Saturn is about 750 million miles away, and when it is farthest, it is over a billion miles away. Saturn is made mostly of hydrogen and helium gas. It is believed to have a rocky or metallic core, but this has not yet been confirmed due to the high atmospheric pressure at the core, which would crush any probe we sent there. Like Earth, Saturn’s axis of rotation is tilted, causing it to experience seasons as it orbits the Sun, though they are far longer than our seasons, lasting 7.5 years.
The most distinctive feature of Saturn is its system of orbiting rings, which are made of ice, dust, and small rock fragments and extend 175,000 miles from the planet, but are about as thick as the width of a football field. There are many ring segments with gaps between them, the largest of which is the Cassini division, which separates rings A and B. This division can be seen in almost any good amateur telescope.
Saturn is the most distant planet visible to the naked eye under most viewing conditions, appearing between a brightness of magnitude 0 to 1, similar to most of the brightest stars and easily visible through severe light pollution. The next planet out, Uranus, appears as a dim star to the naked eye under dark skies, while Neptune is just beyond the reach of unaided viewing even under perfect conditions, requiring binoculars to spot.
When Can I See Saturn In The Night Sky?
The best time to look at Saturn is when the planet is at opposition, which occurs about once every 12 and a half months as Saturn moves slowly around the Sun relative to Earth and thus only shifts slightly eastward amongst the constellations each year. Saturn will next be at opposition in August 2023, September 2024 and 2025, and October 2026. At opposition, a planet rises exactly around sunset and sets at sunrise, and will be at its closest distance to Earth and thus at its biggest and brightest.
Saturn moves gradually westward across the sky with the constellations as the Earth goes around the Sun, and appears to wobble among the constellations as our own planet circles around, slowly wandering eastward as the years go by at a rate of around 5-7 degrees per year, or 10-14 times the angular size of the full Moon.
Saturn can occasionally line up in the sky with the Moon and appear to pass behind it in what is known as an occultation, while the planet itself can similarly occult bright stars such as Aldebaran. Rarely, other planets line up in the sky with Saturn in what is known as a conjunction; an extremely close one occurred with Jupiter in 2020 when both planets were visible in the same telescopic field of view for a couple of nights and their moons appeared to overlap.
The best time of night to view Saturn is when it is high in the sky, as the atmosphere can cause the light from the planet to be scattered and the image to be blurry. Local factors, such as heat shimmering from nearby buildings or pavement, can also affect the view of Saturn and any other planets. You also need to make sure that your telescope is cooled down and collimated, and that your magnification does not exceed the limit of your seeing conditions or telescope. Atmospheric conditions can make magnifications of over 100x look like you’re viewing from the bottom of a swimming pool, and a typical “good” night might allow 300x. Magnifications of 500x or more are only within the grasp of huge telescopes and once-in-a-decade seeing conditions. A typical telescope with good optics is best used at a magnification of no more than 30-40x per inch of aperture for viewing Saturn, even on a clear and steady night.
How Good Of A Telescope Do I Need To See Saturn?
Saturn can be seen with the naked eye, even in areas with light pollution, and it is relatively easy to find in the night sky because it follows an imaginary path called the ecliptic plane that runs east to west across the sky. This is the same path followed by the Sun, Moon, and other planets.
Binoculars with a magnification of 10x or greater can be used to confirm that Saturn is not a star because it appears slightly oval-shaped, although they will not be powerful enough to show the rings – Galileo’s telescope was unable to resolve the rings clearly at a similar magnification.
Any telescope will reveal the rings at a magnification of 30x or greater under almost any viewing conditions, along with at least a couple of moons.
What Does Saturn Look Like In A Telescope?
The rings of Saturn are clearly visible at magnifications of around 30x or more in even the worst telescopes; 100x or more is best for resolving the Cassini division in the rings and cloud belts on the planet itself, which can be seen with any instrument of 3” aperture or greater. Saturn’s cloud belts are tan, beige, and brown in color. They are nearly perfectly linear bars, and rarely ever have storms or significant changes in color and size. Saturn’s poles appear gray-blue and are home to unusual hexagonal storms, though the hexagon shape is nearly impossible to resolve with a backyard telescope.
Additional gaps in Saturn’s rings besides the Cassini Division can be seen with 10” or larger instruments under very good seeing conditions. The Encke gap is the only one that is regularly observed, despite the presence of numerous larger gaps. The Encke gap is the easiest gap to see besides Cassini due to the fact that many of the other gaps are not entirely clear of ring material and thus do not contrast enough with the surrounding rings to be observed. The Maxwell Gap can also be observed with 10” or larger telescopes but is much more difficult to see than the Encke gap and requires extremely steady skies and sharp optics.
Saturn has a tilted axis of rotation similar to Earth, though slightly more extreme at 27 degrees, and thus has “seasons” about 7.5 years long, or ¼ of its orbital period, just like Earth. Every time Saturn reaches equinox, or about once every 15 years, Saturn’s rings can briefly appear edge-on, causing them to virtually disappear due to their thinness. The next occurrence of this phenomenon, known as a ring plane crossing, will take place in 2025. The rings will only disappear for a few weeks around the ring plane crossing, however, before they appear once more.
The tilt of the rings is responsible for dramatic changes in Saturn’s brightness as the rings are more reflective than the planet itself but equal in surface area; a heavier degree of tilt also means it’s easier to see gaps in Saturn’s rings and the shadow of the planet on them. As such, you are probably out of luck attempting to observe the Encke or Maxwell Gap for the next few years until 2028 or so, when the rings reach a significant degree of tilt again, culminating at Saturn’s next solstice in 2033.
Saturn has several moons that can be seen with telescopes. Titan, the largest moon, can be seen in binoculars and appears as an orange-gold disk in large telescopes; its surface is hidden by methane smog in its atmosphere, which creates the ruddy color we see. Titan is as big as the planet Mercury or Jupiter’s moon Ganymede, and only a bit smaller than Mars, with an atmosphere made of nitrogen slightly thicker than that of Earth. Titan is the only known moon with an atmosphere and has many of the ingredients needed for life, though it is extremely cold owing to its smoggy surface and distance from the Sun. Titan has lakes and seas made of liquid methane, which rains and snows from the atmosphere. The Huygens probe landed on Titan in 2005, and NASA is sending the Dragonfly nuclear-powered drone to explore Titan in the 2030s.
Unlike Jupiter, which has four very large planet-like moons and many small asteroid-like bodies, Saturn hosts 7 more large moons, but none are even close to the size of our own or Titan. Rhea, Tethys, and Dione are smaller moons closer to Saturn than Titan that can be seen in telescopes with 4” or larger apertures, and range from about ⅓ to ½ the diameter of our own Moon in size with a composition of rock and ice.
Iapetus orbits far beyond Titan and is about 40% of the size of our Moon, but it features a dramatic two-toned surface, with one side a dull brown and the other reflective white. The dull side of Iapetus makes it hard to see in a telescope less than 6-8” of aperture when it faces us, but the bright side is visible in 4” and larger instruments. This discovery was made very early on in the history of the telescope. Iapetus may have had rings of its own, as its equator is belted by a huge ridge that may be debris from a fallen ring system.
Iapetus can be seen transiting in front of Saturn in years before and after ring plane crossings with a 16” or larger telescope. Transits of the other aforementioned moons can be seen around ring plane crossings. Titan’s shadow and disk can be seen with 10” or larger telescopes during these transits, and the transits of Rhea, Tethys, and Dione can be seen with 16” or larger telescopes under very steady skies.
Mimas and Enceladus are the smallest round moons of Saturn, hovering around 15% of the size of our Moon and a tiny fraction of its mass. Mimas looks much like the Death Star from Star Wars due to the presence of a huge crater in its northern hemisphere, while Enceladus is made mostly of ice.
Enceladus is made mostly of ice and features unusual bluish stripes on its terrain, a mostly smooth surface, and geysers erupting from its liquid water ocean beneath the icy crust. Enceladus’ ocean is kept heated by the gravity of Saturn and nearby moon Dione. Enceladus may be a prime candidate for hosting extraterrestrial life, as it seems to have a warmer interior than Jupiter’s similar but larger moon Europa; heat is needed both to keep water liquid and trigger the chemical reactions that may create life. Microbial life may exist in Enceladus’ sea and could be sampled by a spacecraft flying through the geysers like bugs on a windshield. NASA plans to send a mission to Enceladus in the 2040s.
Both Mimas and Enceladus require a 6” or preferably 8” or larger telescope to be seen. Their disks are beyond the range of being visible in any backyard telescope during a rare transit. The last observable moon of Saturn is Hyperion, a sponge-shaped rock only a couple hundred miles wide but one of the largest non-round objects in the Solar System. Hyperion orbits just past Titan, far enough from Saturn’s glare that it can still be seen most of the time with a suitably large instrument of 12” or greater aperture.