Is there a solar flare right now?

The Sun is a star, a huge ball of hot gas held together by its own gravity and lit by fusion in its core. Its gas is electrically charged, and its churning makes strong, tangled magnetic fields. Where they push up through the surface, we see dark sunspots.

Above a group of sunspots, the twisted field can snap into a calmer shape. It lets go of its stored energy within minutes, as a burst of light across every colour, from radio waves to X-rays. That burst is a solar flare. NASA calls flares the most powerful explosions in the solar system.

Here on the ground we are safe. Earth's air and its magnetic field, the shield we live inside, stop a flare's harmful radiation long before it reaches us.

Flares are measured by how brightly they shine in X-rays, as seen from Earth's orbit. NOAA's GOES satellites watch the Sun's X-rays without a break, and the strongest reading of a flare gives it a letter: A, B, C, M or X.

Each letter is ten times the one before. So an X flare is ten times an M, and a hundred times a C. A number adds detail inside a class: an M2 is twice an M1. The X class has no top, because nothing caps how strong a flare can be.

On a quiet day the Sun sits in the B or C class, with small flares coming and going. Right now it reads B1.8. Big flares come most often near the peak of the Sun's 11-year cycle, when it is crowded with sunspots.

A flare's X-rays and ultraviolet light travel at the speed of light. They hit the top of our atmosphere on the side of Earth facing the Sun at the moment we see the flare, with no warning at all.

The extra light charges up the lower layers of the ionosphere, high above our heads. Shortwave radio normally bounces off the layers above, which lets pilots and sailors talk across oceans. During a strong flare those signals are swallowed instead. That is a radio blackout, and it lasts from minutes to hours. NOAA's blackout scale starts at the M class.

The last flare of class M or X began on 19 October 2026. Flares often come with a second eruption, a cloud of charged gas called a coronal mass ejection. That cloud is far slower than light. If it is aimed at Earth, it can arrive a day or more later and set off a geomagnetic storm.

The strongest flare ever measured erupted on 4 November 2003, at the end of a burst of activity around Halloween. It was so bright that it overwhelmed the X-ray sensor on the GOES satellite for 12 minutes. Working from the parts it did record, NOAA estimated its peak at X28. The flare went off near the edge of the Sun, pointing away from us, so Earth escaped the worst.

In the cycle we live in now, Solar Cycle 25, a great flare came on 3 October 2024. It peaked at X9.0. When it erupted, NOAA called it the most powerful flare so far in this cycle.

GOES has measured the Sun's X-rays only since 1976. The great flare that Richard Carrington saw by eye in 1859 came long before, so nobody knows its class. It was followed by the largest geomagnetic storm on record.