One of the sun’s sunspots has gotten so large that it can be seen from Earth without magnification—but not without eye protection.
Sunspot AR3310, a dark patch on the sun facing toward us, has grown to such a size that a telescope is not required to spot it from Earth. South Korean astronomer Bum-Suk Yeom uploaded a graphic of the sunspot, showing its scale next to a tiny planet Earth.
“Naked-Eye Sunspot using Solar Glasses (or Solar Filter),” Yeom said in an Instagram post sharing the image. “A giant sunspot, visible to the naked eye, is crossing the sun’s disk. A [sunspot] can be seen to the left of the center of the solar disk.”
Sunspots are dark areas on the sun’s surface caused by regions of particularly strong and twisted magnetic fields. If these fields are strong enough, they prevent some heat from the sun’s core from reaching its atmosphere, resulting in the surface being cooler and appearing darker.
Sunspots are occasionally large enough to be viewed with the naked eye—and with eye protection against the sun’s powerful glare.
“The minimal visibility threshold is estimated as [roughly] 425 millionths of the visible solar disk—0.04 percent of the solar disk—whereas larger sunspot area and favorable meteorological conditions improve their visibility,” Hisashi Hayakawa, a solar physicist at Japan’s Nagoya University, previously told Newsweek.
The Earth’s surface area takes up only around 169 millionths of the solar disk. In his post, Bum-Suk estimates that sunspot AR3310 is about four times the size of the Earth.
Because of their active magnetic fields, sunspots are usually the points of the sun from which solar flares are emitted or coronal mass ejections occur. Solar flares are the muzzle flash of a solar eruption, sending X-rays out into space. CMEs are the bullet: plumes of solar plasma and a magnetic field traveling at immense speeds. If either of these solar ejections hits the Earth, it can trigger geomagnetic storms, causing auroras across the middle latitudes and occasionally radio blackouts.
As the sun progresses through its 11-year solar cycle, the number of sunspots varies. At the solar maximum, solar activity peaks and the sun has many more sunspots than during the minimum six or so years later. There have been 25 of these cycles of activity since they were first recorded in 1755. The last solar minimum occurred in 2019, and the next solar maximum is forecast for 2025, according to the National Oceanic and Atmospheric Administration’s Space Weather Prediction Center.
However, the current solar cycle appears to be exceeding the initial predictions. Solar Cycle 25 has now outperformed the official forecast for over 24 consecutive months, with sunspot numbers already nearing the scale of those seen during the maximum of the previous cycle.
Those trying to catch a glimpse of this unusually large sunspot are warned to not look directly at the sun. Bum-Suk said in his post that solar glasses or solar filters are essential to protect the eyes.
“I would recommend you to use eclipse glasses,” Hayakawa also said. “Don’t directly see the sun, even through smoked glass. Your eyes will be burnt. Some historical astronomers significantly reduced their eyesight owing to their solar observations.”
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