It's not every day that a prominent feature of our solar system disappears, but that's precisely what will happen with Saturn. Over the weekend, Saturn's gorgeous rings will nearly vanish from sight. No worries, they'll be back in a couple of weeks.
This phenomenon is caused by an optical illusion that occurs when the stars line up. Saturn is tilted at 26.73 degrees on its orbit, while Earth is very close to that at a 23.5-degree tilt. When the two planets line up just right, the rings of Saturn are almost entirely horizontal from the perspective of Earth, causing them to mostly vanish.
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"As Saturn and the Earth travel around the sun, we will periodically be in a position where those rings are seen edge on," explains Dr. Shannon Schmoll, director of the Abrams Planetarium at Michigan State University. "Because the rings are so thin, if we look at it edge-on, we can't see (the rings)."
So, anyone looking up at the sky this weekend will likely note that the planet won't look very Saturn-like without its trademark rings. However, if you're using a powerful telescope, the rings will still be visible. It'll appear as though a thin line is running through the middle of Saturn, as shown in the graphic above.
How do Saturn's rings disappear?
Saturn's rings look like a line when they're lined up.
The tilt of Saturn and Earth is the main thing. It's like looking at a piece of paper. If you hold it horizontally up to eye level, it'll be practically invisible. Paper is an apt analogy here because Saturn's rings are thinner than many think.
"The rings of Saturn are incredibly thin," Schmoll says. "Even the thickest estimates put the rings at 1 kilometer (about half a mile). Saturn's diameter is over 116,000 km, so comparatively that is VERY thin."
According to NASA, Saturn's rings average about 30 feet in height across the entire length of the ring. That means when viewed from the side at a distance of about 1.5 million kilometers (983,000 miles), you might as well be looking at a sheet of paper from the side.
The rings are still technically visible. Folks with higher-powered telescopes may be able to see the line jutting across Saturn. However, those with low-power telescopes may not see it, making Saturn look naked.
When will the rings return?
The peak of this little celestial dance will occur over the weekend. So, technically, the rings have already been like this for a week or two and will continue to be difficult to see going into April. By then, Saturn's orbit will begin to tilt the rings again, and they will slowly come back into view over the next month or two.
"Technically, the ring plane crossing is only for a moment when it's fully edge on," said Schmoll. "For powerful telescopes, we can see the rings again quickly. For most backyard telescopes, though, you have to wait a few months before you can see them again"
How rare is this event?
According to NASA, this happens about every 13 to 15 years on average. It's not an exact science, though, as prior events occurred in 1980, 1995 and 2009.
"Saturn's orbit is just under 30 years, so there are two times in a Saturn orbit when that angle is just right," Dr. Schmoll says. "Sometimes it happens when Saturn is on the opposite side of the sun from us, which makes it hard to see because the sun gets in the way."
The next one is predicted to come in 2038 or 2039, Schmoll says, and it should be "a lot easier to spot" as well.