A quadruple Saturn moon transit.
Saturn, like the Earth, is tilted with respect to its orbit around the Sun. Our tilt is about 24 degrees, and Saturn’s is about 27. This means that twice every Saturn year (which are roughly 30 Earth years in length) we see Saturn’s rings edge-on. They can get so thin they practically disappear! That happens in September of this year, and as you can see from the image above image, our viewing angle of the rings is currently very shallow.
The icy particles in the rings orbits over Saturn’s equator, just as the moons do. That means that if we’re seeing the rings nearly edge-on, the orbits of the moons are that way as well. This makes transits — moons moving across the face of the planet — more common. So on February 24 of this year, Hubble was able to snap a spectacular series of images of four of Saturn’s moons projected on Saturn’s visage. You can see how the moons moved in the image below, showing the time-sequence Hubble took of the event.