New Delhi: Sunday night brought with it a celestial illusion: the spectacular rings of Saturn vanished momentarily. They did not disappear in reality but just edged out of our line of sight, making them invisible to human eyes. The rare phenomenon known as “ring plane crossing” captivated skywatchers across the globe. And it is not the first time, it occurs roughly every 13-15 years.
NASA posted a short video of Saturn rotating as its rings slowly faded from view. “Saturn’s rings have disappeared! (Kind of.) Due to their tilt from the perspective of Earth, the planet’s rings have appeared to vanish. But don’t worry – as Saturn continues to rotate, the rings will become visible again,” the caption read on X.
Why do the rings appear to vanish?
As Saturn tilts on its axis while orbiting the Sun, the apparent angle of its rings changes from Earth’s perspective. During a ring-plane crossing, the rings appear to narrow, and at the exact alignment, they can seem to vanish entirely. Saturn takes 29.5 Earth years to complete one orbit around the sun.
It is the slow progression of Earth and Saturn through their orbits that dictates the apparent appearance and disappearance of the rings.
A similar crossing occurred in 1995, followed by another in 2009. Saturn, often called the jewel of the solar system, has rings roughly 2,70,000 kilometres in diameter, yet their vertical thickness is only about 10 metres. On the day of a ring-plane crossing, the rings appear extremely thin from Earth, fading almost completely into the background sky.
This year, two such crossings were witnessed: one was in March when Saturn was closer to the sun and was lost in its glare. This time, the planet was positioned up in the evening sky, making it a delight for the skywatchers.
On Sunday night, Saturn appeared as a yellow, flattened, ringless disk.
The rings confusion
It was some 400 years ago, when Saturn was observed through the telescope, and its disappearing rings caused confusion. At the heart of it was the famous astronomer Galileo Galilei. Michael Shank, an emeritus professor of history at the University of Wisconsin-Madison, told The New York Times that Galilei had observed Saturn in July 1610 with a self-made “spyglass”. However, the sight caught him off guard because he couldn’t “properly resolve the rings”.
“Nobody back then suspected planets could have rings,” Shank told the international newspaper. So, Galileo named the rings “lateral bodies” around the planet.
However, a few years later, when Galilei observed the planet again, he was taken aback as there were no rings. This confusion was resolved in 1659 after Dutch physicist Christiaan Huygens concluded that what Galilei had seen were not lateral bodies but rings around the planet.
Saturn is not going to be adorned by its rings for long. A NASA research in December 2018 revealed that the planet was losing its iconic rings at the maximum rate estimated from Voyager 1 & 2 (twin NASA spacecraft launched in 1977). The rings are being pulled into Saturn by gravity as a dusty rain of ice particles under the influence of Saturn’s magnetic field, the NASA press release read.
“We estimate that this ‘ring rain’ drains an amount of water products that could fill an Olympic-sized swimming pool from Saturn’s rings in half an hour,” said James O’Donoghue of NASA’s Goddard Space Flight Centre in Greenbelt, Maryland.
(Edited by Ratan Priya)