Solar Activity

The Solar Dynamics Observatory, launched by NASA in February 2010, photographs the Sun every 12 seconds in multiple wavelengths simultaneously. Each wavelength reveals a different layer of the solar atmosphere, at a different temperature.

The 171 Angstrom channel shows the corona at around 600,000°C - the classic golden SDO view where active regions glow intensely. The HMI continuum shows visible light, the view closest to what a solar telescope would see, with sunspots appearing as dark patches. The 304 Angstrom channel reveals the chromosphere at 50,000°C, highlighting prominences - enormous arcs of plasma suspended above the surface. The 193 Angstrom channel shows the hottest coronal structures at 1.2 million°C, where coronal holes (dark regions where the solar wind escapes into space) are clearly visible.

Every 11 years, the Sun's magnetic field reverses its polarity. The north magnetic pole becomes the south pole and vice versa. This cycle drives a dramatic rise and fall in solar activity - from the quiet minimum (few or no sunspots, minimal flare activity) to the stormy maximum (hundreds of sunspots, frequent powerful flares and coronal mass ejections).

The butterfly diagram below the viewer shows this pattern clearly. At the start of each cycle, sunspots appear at high latitudes (around 30 degrees from the equator). As the cycle progresses, new spots emerge closer and closer to the equator. By the end of the cycle, activity is concentrated near the equator, and the next cycle's spots begin appearing at high latitudes again. This migration pattern, when plotted on a latitude-vs-time chart, creates a shape resembling butterfly wings - hence the name.

Sunspots are not blemishes or imperfections. They are regions where intense magnetic fields (thousands of times stronger than Earth's) break through the surface. The magnetic field suppresses convection, preventing hot plasma from rising from below. The result is a region that is cooler than its surroundings - about 3,500°C compared to the 5,500°C of the normal photosphere. This temperature difference makes sunspots appear dark, though a sunspot on its own would be brighter than the full Moon.

Sunspots typically occur in pairs or groups with opposite magnetic polarity, connected by arching magnetic field lines. It is along these field lines that solar flares and coronal mass ejections originate. The larger and more complex the sunspot group, the more likely it is to produce a powerful eruption.

Solar flares are sudden releases of magnetic energy, producing intense bursts of radiation across the electromagnetic spectrum. They are classified by X-ray intensity: C-class (minor), M-class (moderate), and X-class (major). An X10 flare is ten times more powerful than an X1. The radiation arrives at Earth in just 8 minutes (the speed of light) and can cause radio blackouts on the sunlit hemisphere.

Coronal mass ejections (CMEs) are more dangerous. They are massive clouds of magnetised plasma, billions of tonnes of solar material, launched into space at speeds of 250 to 3,000 km/s. When a CME hits Earth's magnetosphere, it can compress and distort the magnetic field, inducing electric currents in long conductors - power lines, pipelines, and undersea cables. A sufficiently powerful CME could damage transformers, disrupt satellite electronics, and degrade GPS accuracy.

The same geomagnetic storms that threaten infrastructure produce aurora - the northern and southern lights. During the May 2024 G5 storm, aurora was visible across most of the United Kingdom, the continental United States, and parts of northern Mexico. It was the most widely observed aurora in human history, partly because of the storm's intensity and partly because hundreds of millions of people carry high-quality cameras in their pockets.