Sun’s Strongest Flare in Weeks Could Push Aurora South Friday

At 4:50 p.m. ET on Tuesday, a patch of the sun called Active Region 4479 let go of the most powerful flare it has produced all week. NASA’s Solar Dynamics Observatory, which watches the sun continuously, caught the moment as a bright white flash against the star’s teal-colored disk.

The flare measured X1.1 on the scale scientists use to rank these events — X-class is the most intense category, and the number that follows measures relative strength within it. It was strong enough to trigger a brief but real R3 radio blackout across the sunlit side of Earth, degrading high-frequency radio signals for pilots, ships and amateur radio operators across the Americas for the better part of an hour.

What actually crosses 93 million miles

The flare itself is light — X-rays and extreme ultraviolet radiation that reach Earth in about eight minutes and cause the radio disruption. What matters more for the days ahead is what came with it: a coronal mass ejection, a separate cloud of magnetized solar plasma that left the sun in every direction at roughly 1,500 kilometers per second, or about 3.3 million miles per hour. Unlike the flare’s light, the CME takes days to arrive, because it is physical material, not radiation, crossing the distance between the sun and Earth.

NOAA’s Space Weather Prediction Center issued a G2 — Moderate Geomagnetic Storm Watch for Friday, July 3, based on that CME’s projected arrival. The agency’s forecast calls for weaker G1-level conditions Wednesday, a lull Thursday, and the moderate storm settling in Friday. G2 storms are common enough — this is a fairly routine event by the standards of an active sun — but they are strong enough to push aurora well south of its usual polar range.

NOAA says the aurora could become visible as far south as New York, Wisconsin and Washington state, provided skies are dark and clear. That is a real possibility, not a guarantee: geomagnetic storms are notoriously hard to forecast precisely, and the same CME could also deliver only a glancing blow, as a similar event did earlier this week. Potential effects, mostly confined to areas near the poles, include minor power-grid voltage fluctuations, small satellite-orientation errors and added drag on spacecraft in low orbit — not the kind of disruption that reaches the ground for most people.

This is the ninth flare at M-class or stronger from the sun’s active regions in the past week, part of a stretch NOAA calls elevated but not extreme for this point in the solar cycle. Active Region 4479 remains capable of another X-class eruption, the agency said, with a slight chance of a minor solar radiation storm. Three days after the Vera Rubin Observatory started its ten-year survey of the night sky, the sun gave skywatchers a far more immediate reason to look up — assuming the clouds cooperate Friday night.