It is that time of year again where those “once in a lifetime” kind of astronomy hoaxes begin circulating on social media and wow an uninformed crowd. Here’s a hoax which I came across today purporting that Saturn will appear closer to Earth than the moon to offer an spectacular sight. Anyone with a basic understanding of astronomy will of course likely not get sucked into such an obvious fake. I was surprised however to find that the photo was heavily shared with thousands of people gullibly awaiting the falsely supposed sight.
I initially thought that this was a sarcastic meme, intended to make fun of those kinds of posts until I clicked on the shares and saw the sheer amount of people who genuinely plan to watch the sky tomorrow.
Saturn can never appear that big. The closest that Saturn and Earth can get to each other is 1.2 billion kilometres. That’s when opposition occurs. Earth overtakes Saturn at which point they are 180 degrees from each other and are at the same side of the sun. Since Saturn takes about 30 years to circle the sun and Earth takes just one year, Earth will overtake Saturn once every 378.1 days (about 12 months and 2 weeks). Thus, the oppositions recur each year with a 2 week increase. Last year, for instance, the opposition occurred on May 23rd. This year, it is expected to occur on June 3rd. Due to the elliptical nature of the orbits however, some oppositions will be closer than others.
A rare astronomical phenomenon called ring plane crossing occurs every 15 years, at which point Earth passes through Saturn’s ring plane and Saturn’s rings are tilted edgewise towards the Earth while the north pole tilts away from the sun. When the Northern Hemisphere is tipped towards the Earth, the rings come back into view.
Nothing of the incredibly exaggerated magnitude such as that portrayed in the hoax can occur in any way. Saturn’s closest approach to Earth in 30 years occurred in 2002 when Saturn was at its perihelion (closest approach to the Sun). It was brighter than all the other stars except Sirius but even then it was just a bright yellow speck in the sky (within 1.2 billion km away). One would have had to use a telescope to make out the rings. If Saturn were that close, Earth would have been long gone.