Why Do Saturn's Rings Disappear?

Saturn, of course, is famous for its rings. It’s these rings that make the planet the jewel in the solar system and draw countless observers to the eyepiece whenever it’s visible. You could argue that Saturn is astronomy’s biggest recruiter, with more people getting hooked on the hobby after seeing the planet than any other celestial sight.

But every now and then, Saturn pulls a now-you-see-them, now-you-don’t magic trick, and the rings disappear altogether. How can this happen? When does it happen? And how can you see this for yourself?

Look through a telescope at Saturn on any given night, and you’ll see the planet - and, of course, it’s rings - but that’s not to say the view will remain the same forever. From month to month, both the Earth and Saturn move along in their orbits and Saturn appears to grow smaller and larger, fainter and brighter, as the distance between the two worlds waxes and wanes.

However, from year to year, something else becomes apparent. Depending on when you look, you may notice that the rings appear as wide bands encircling the planet. Look again a year later, and you may notice the rings appear a little thinner.

Conversely, it could be that the rings appear relatively thin one year and then wider the next. So why is that? Are the rings moving? Or is something else having a strange effect on the planet?

The Rings That Appear to Disappear

It all comes down to Saturn’s axial tilt. All the planets are tilted over, to some extent or another, with Mercury having an almost non-existent tilt of 0.03 degrees and Uranus rolling around on its side with a tilt of 82.23 degrees.

Earth has a respectable tilt of 23.44 degrees, which is why we have seasons. In June, the northern hemisphere is pointed toward the Sun, and so the inhabitants of that hemisphere experience a warmer climate - summer. At the same time, the southern hemisphere is pointed away from the Sun, and therefore, the climate is colder and the inhabitants there experience winter.

In December, the opposite is true, and those in the northern hemisphere shiver in the winter cold, while those south of the equator enjoy their summer warmth. Saturn’s axis is tilted by 26.73 degrees, and it has seasons too. The difference is that Saturn takes nearly 30 years to orbit the Sun, and so each season lasts roughly 7.5 years!

From our point of view, this changes the angle at which we see the planet’s rings. When it’s summer in the Saturnian northern hemisphere, the planet’s northern polar region is pointed toward us, and we see the upper side of the rings. When it’s summer in the southern hemisphere, the southern polar region is pointed toward us, and we see the underside of the rings. At both times, the rings appear wide open to us.

Image Credit: NASA, ESA, and Amy Simon (NASA-GSFC); Image Processing: Alyssa Pagan (STScI)

However, as the planet moves along its orbit, the angle of the tilt lessens and the rings appear to narrow. When the planet is upright, with no apparent tilt (the equivalent of Saturnian spring or fall), the Earth crosses the plane of the rings, and the rings appear edge-on to us.

This is when, for a short period of time, they disappear from view. Since the rings are no more than 0.6 miles (1 km) thick, they’re so thin that it’s like trying to see a flat sheet of paper from miles away. Essentially, from our point of view, the rings simply vanish.

From Body Parts to Planetary Rings

This phenomenon is not a recent discovery and has actually been known for hundreds of years. The Italian astronomer Galileo Galilei first noticed the rings in 1610, but telescopes were a relatively new invention at the time, and his homemade version was incapable of showing the rings for what they were.

Instead, the planet appeared to be accompanied by two other worlds, one on either side of the planet, and each about a third of the size of Saturn itself. He even went so far as to describe them as being like ears.

Two years later, Galileo became very confused when he turned his telescope toward the planet again and noted that the two accompanying worlds had apparently disappeared. Later, he noticed that the phenomena had returned, but this time, since the rings appeared narrower than before, he described them as arms.

In 1659, the Dutch astronomer Christiaan Huygens published his theory that Saturn was “encircled by a ring, thin, plane, nowhere attached” and that, thanks to Saturn’s tilt, “the same ring showed to us at one time a rather broad ellipse, at another time a narrower ellipse, and sometimes even a straight line.”

Top drawing: Galileo's drawing of Saturn, 1610. Bottom drawing: Galileo's drawing of Saturn, 1616

How Can I See the Rings Disappear for Myself?

The idea of disappearing rings might sound improbable, or even impossible, but it’s easy enough to witness this phenomenon for yourself. You just need to be patient, as the process is too slow to notice any difference from night to night.

Also, while the planet is easily visible to the naked eye, you’ll need a telescope to see the rings themselves. You won’t need a particularly high magnification - around 40x or 50x - but a higher magnification with the right quality equipment will provide the best views.

Since Saturn takes 30 years to orbit the Sun, and the rings only appear edge-on to us during the Saturnian spring or fall, there’s roughly a 15-year gap between each ring plane crossing.

When the rings are at their widest, you won’t see much difference from year to year, but as the planet moves along its orbit, you’ll notice the rings gradually narrowing. The closer the planet is to the ring-plane crossing, the quicker the rings will appear to narrow, with changes potentially becoming noticeable from month to month or even from week to week.

Eventually, in the weeks and days prior to the ring plane crossing, the rings will disappear. How long you’ll continue to be able to see the rings will really depend on several factors:

  • The planet’s location in the sky, relative to the Sun.
  • The equipment you’re using. The larger your telescope’s aperture, the more light it can gather and the easier it will be to see the rings as they narrow.

The last time this happened was on September 4th, 2009, when the planet was in the constellation Virgo. At that time, the planet was visible in the evening sky but fairly low in the west after sunset.

When Can I Next See Saturn’s Rings Disappear?

The next ring plane crossing will occur on March 23rd, 2025, but unfortunately, things are worse at that time. Saturn will be in Aquarius, but since that constellation is best seen in the fall, it will be too close to the Sun to be visible on that date.

Realistically, your last chance to get a good view of the planet in the evening sky will be a little more than two months earlier. Around mid-January, Saturn will still be reasonably high over the southwestern horizon a few hours after sunset, when the skies are truly dark. This will allow you to get a good look at the planet.

The rings themselves will still be noticeably open, if narrow, at that time. After that, the rings will continue to close, but observing the planet will become harder as it loses ground against the Sun.

Saturn is in conjunction with the Sun on March 12th, just 10 days before the ring plane crossing, with the planet emerging into the predawn twilight about three or four weeks later. It’ll appear low over the eastern horizon at that time, close to Venus and Mercury, but the chances are it’ll be too low, and the sky will be too bright to be worth observing telescopically.

Past that, you’ll have to wait until mid-June for the planet to be sufficiently far from the Sun to make observations worthwhile. Go outside a few hours before dawn, when the sky is still dark, and the planet will be nearly 30 degrees above the south-southeastern horizon, with the rings appearing narrow but readily seen.

Image Credit: Alan Friedman

(Incidentally, the next ring plane crossing after 2025 occurs on October 15th, 2038, slightly more than a month after Saturn is in conjunction with the Sun.)

When Can I See Saturn’s Rings at Their Thinnest?

While, unfortunately, you won’t be able to see Saturn’s rings disappear completely in 2025, you can still challenge your observing skills near the end of the year.

The planet reaches opposition on September 21st and will be visible throughout the entire night, from sunset to sunrise. This makes it the best time to observe the planet, and it’ll remain visible in the evening sky until the following March.

Turn your telescope toward Saturn at opposition and you’ll see the rings are still narrow, but come back a week later, and you may notice the rings are actually closing again. That’s because, of course, the Earth is also orbiting the Sun, and as it does so, its own axial tilt is causing the angle of our viewpoint to change.

Keep coming back to Saturn and you’ll see the rings becoming thinner and thinner. They won’t be completely edge-on, but the chances are they’ll be increasingly difficult to spot, with the rings being narrowest on November 23rd. If you’re able to see them at all at that time, the chances are they’ll only appear as a thin line crossing the center of the planet’s disc.

After that, they’ll widen again, and although they’ll temporarily close a little in the second half of 2026, they won’t appear anywhere as narrow as they did the previous November.

Capturing the Moment For Posterity

If you’d like to try your hand at imaging Saturn, there are several ways to do it, but it’s worth taking some time to practice first. For example, you can theoretically capture images of the planets with your smartphone, but bear the following points in mind:

  • You’ll need a smartphone adapter to hold your phone steady.
  • You’ll need a wide-angle eyepiece with a short focal length to get the magnification required and to make it easier to align the planet with your phone’s camera.
  • Lastly, you’ll need to adjust your cell phone camera’s settings (eg, ISO, exposure length, brightness, etc) to get the best results.

If you already own a telescope, another inexpensive option is a digital eyepiece camera. This works like a regular eyepiece but allows you to capture the view by connecting the eyepiece to your computer.

If you’re serious about astrophotography, it might be worth investing in a DSLR camera and using a T-adapter to attach it to the telescope.

Regardless of how you do it, you’ll also need a motorized telescope that follows the planet (computerized scopes are a great choice for beginners), otherwise, it will quickly move across the field of view. Without tracking, the planet will be difficult to image, and whatever you capture will be blurry.

Lastly, it’s worth shooting video with your camera and then using software, such as PixInsight, to extract, stack, and process the best of the individual frames. This will result in a sharper, more detailed image.

On any given night, nothing can beat Saturn and its rings, but the chance to see Saturn without its rings is a rare opportunity indeed. Miss this one and you’ll find yourself with a long wait until 2038 comes around!

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