If you’re a North American who has acquired eclipse glasses early for the
Big sunspots do not always produce large solar flares, but there is a connection. Consequently, it’s quite plausible we will soon witness X-flares associated with AR3576. If we don’t, we can still expect to encounter them before this solar cycle is over – after all we
What are solar flares?
As we know, the Sun is a constant source of light, which is a form of electromagnetic radiation, and it also radiates at other wavelengths. Every now and then, however, a small (or sometimes not so small) part of the Sun releases more electromagnetic radiation than usual. The extra brightness is not so great that we notice the Sun as a whole getting brighter, but if we have telescopes trained on the area, we can see the brightening patch.
Flares are a consequence of irregularities in the Sun’s magnetic field. Initially, the field will block some of the heat rising from the center of the Sun, causing a sunspot. However, when the field gets tangled or reorganizes, the energy released can accelerate charged particles through the Sun’s atmosphere, producing a swift extra burst of energy.
The larger the sunspot, the greater the flare potential, but the relationship between them is far from perfect. Both rise and fall with the 11-year solar cycle, the peak of which we have either just seen, or will see soon.
A big spot does not guarantee big flares, but it certainly raises the chances.
How are solar flares categorized?
Flares are categorized into five classes based on the peak flux in watts per square meter (W/m2), counting only the energy released at between 1 and 8 Angstroms (known as soft X-rays). For decades, successive Geostationary Operational Environmental Satellites (GOES) have had the job of measuring the energy released by flares so they can be classified.
The smallest flares, A-class, peak at less than 10-7 W/m2, which is almost too small to notice at our distance. B and C classes (respectively 10-7-10-6 and 10-6–10-5 W/m2) are of interest to solar astronomers, but have little effect on most people.
The largest flares, those with more than 10-4 W/m2, are called X-class. There is no theoretical limit on how large the X-class can be. Within the other classes, flares are subdivided 1-10, but the largest flare encountered by GOES was so powerful it saturated its detectors, leaving astronomers to estimate its size at X40-X45.
An X-flare’s number indicates how many times as energetic it is as an X1 flare, so an X9 is nine times as powerful as an X1, around 9 x 10-4 W/m2.
Are solar flares a threat?
Definitely, but also not directly.
The first thing to note is that the problem is seldom the flares themselves. The threat arises from
Most flares don’t produce CMEs, but the larger a flare is, the more powerful a CME it can trigger.
As you probably noticed, the world suffered no serious consequences from recent X-flares, but the fact that not every X-flare is damaging doesn’t mean none are.
Unsurprisingly, we have more to fear from an X50 flare than an X5. Direction, however, is at least as important as size. Half of X-flares are on the far side of the Sun and we’re only aware of them if a spacecraft happens to be suitably positioned to notice. Even flares that are on the side we can see won’t affect us much if pointed away from the Earth.
The flares we need to worry about are those that are both powerful and score direct hits on the Earth’s magnetosphere.
The standard against which flares are measured is the
Moreover, the Carrington Event may be far from the limit. Tree rings reveal evidence of so-called