Last Monday (11), a “dead” sunspot exploded, releasing large loads of energy in the form of radiation. The event also caused a coronal mass ejection (CME) towards Earth – basically, an exploding ball of plasma from the Sun. And it is predicted to hit our atmosphere tomorrow (14), around 8 am.
But there’s no reason to panic; it does not pose any risk of catastrophic impacts to the planet. What we may feel are the effects of a mild to moderate geomagnetic storm, such as swings in satellite operations or the power grid.
The moment of the solar eruption (flare) was recorded by the Solar satellite dynamicsNASA, and the Royal Observatory of Belgium.
Its most awaited (and beautiful) consequence will be in the sky: a CME usually causes very intense aurora borealis and australis, visible at lower latitudes than normal.
When its electrically charged particles hit the Earth’s magnetic field, they can descend through the North and South Poles, interacting with gases in the atmosphere. This releases energy in the form of photons (particles that make up light), which create the dancing colors and shapes in the sky, which we call “auroras”.
Unfortunately for us, the spectacle is usually seen only in the countries of the polar circles, especially Canada, Finland, Iceland, Norway, Russia and Sweden, in addition to Greenland (Danish territory) and Alaska (USA).
This week, auroras are expected to be more intense over a wider swath of the globe, including places such as the northern United States, New Zealand, and southern Argentina and Chile.
Solar spots and eruptions
Sunspots are those dark regions on the surface of the Sun. They are caused by the intense magnetic and plasma fluxes inside our star, which escape outwards.
They are temporary, lasting from a few hours to a few months. The Sun’s own convection process “kills” these spots, tearing them apart and leaving a magnetically disturbed trail.
The one that exploded this week was sunspot AR2987, which generated a class C eruption, a common type that rarely makes direct impacts on Earth.
A curious detail is that this stain was already “dead”. But how? Days or weeks later, sunspots can “resurrect”, with magnetism reappearing in the same region, and explode again.
Sometimes, like Monday, these “flares” can trigger coronal mass ejections, which are huge eruptions of plasma and magnetic fields from the Sun that travel through space at millions of kilometers per hour. Class C events rarely generate CMEs, but when they do, they are slower and weaker.
Solar activity and auroras
During calmer times on the Sun’s surface, the flow of particles known as the “solar wind” is enough to trigger auroras in the planet’s polar regions.
But during large CMEs, there is a greater perturbation to Earth’s magnetic field, which means that auroras can appear over a much wider zone. They are called “boreal” if they occur in the northern hemisphere, or “austral” in the south.
Currently, the Sun is going through a period of high activity, which explains the greater occurrence of auroras, geomagnetic storms and other recent phenomena. These are the so-called “solar cycles”, which last about 11 years, alternating calm and activity.
This is cycle 25 – that is, the twenty-fifth since formal observations began in 1755. The number of sunspots continues to increase, and is expected to peak in 2025.
*With information from Live Science and SpaceWeather.