Seeing Saturn’s rings in a new light

Views of Saturn from Mt John. On the left captured as white light, on the right using a methane...
Views of Saturn from Mt John. On the left captured as white light, on the right using a methane filter. Photos: Ian Griffin
Viewing Saturn is an unforgettable experience.

I still vividly recall my first encounter with this celestial wonder on a magical Christmas Day in 1972. Peering through a modest Japanese refracting telescope, a gift from my parents, I was captivated by my view. The planet’s yellow-white disk was adorned by a set of dramatic rings, a sight that seemed too fantastical to be real.

The origin of Saturn’s rings is a fascinating tale of cosmic collisions. Two icy moons collided a few hundred million years ago. The resulting debris formed Saturn’s iconic rings and a significant portion of its impressive collection of 146 moons.

I’m mentioning Saturn because it is easily visible in the morning sky. Rising just before 1am, Saturn is in Aquarius, and is almost 50 degrees above the northern horizon at sunrise.

Last weekend, I was lucky to be observing at the University of Canterbury’s Mt John Observatory. After being blasted by gale conditions on Saturday, by the early hours of Sunday, conditions were calm enough to open the dome and point the 0.6m telescope at Saturn. Even though I have viewed the planet thousands of times, I still felt excitement as images of Saturn started coming in.

Our view of Saturn’s rings changes throughout Saturn’s 29-year orbital period thanks to the planet’s axial tilt and its orbit around the Sun. Saturn’s axis is tilted at about 27 degrees, similar to Earth’s, which means as Saturn orbits the Sun, we see its rings from different angles. Sometimes, the rings appear wide open.

As it continues along its orbit, the angle gradually decreases until the rings seem to thin and nearly disappear when viewed edge-on. This happens next year, so Saturn’s rings are relatively close to edge on at the moment.

I put a methane filter in front of my camera for some images, as I wanted to see for myself a fascinating phenomenon. Saturn appears dim through a methane filter because its atmosphere strongly absorbs methane, while the rings, composed mainly of water ice, do not absorb methane and remain bright.