Solar phenomena

Solar phenomena are natural events occurring within the Sun's atmosphere.

These events include solar wind, solar flares, and coronal mass ejections. They also include sunspots and coronal heating. Together, these fluctuations are known as solar variation. This variation creates space weather within the Sun's gravitational field. Understanding these events helps us understand how our star affects our solar system.

These phenomena are driven by powerful magnetic fields. These fields are generated by two different processes. First, a helical dynamo located near the center of the Sun's mass creates strong magnetic fields. Second, a chaotic dynamo near the surface creates smaller magnetic fluctuations. When two oppositely directed magnetic field lines are brought together, magnetic reconnection occurs. This process causes the field lines to rearrange themselves. This rearrangement results in a sudden release of stored energy. This energy release is what powers many solar events.

One major type of event is a coronal mass ejection, or CME. A CME is a massive burst of solar wind and magnetic fields. These bursts rise above the solar corona, which is the Sun's outer atmosphere. Most powerful solar flares are accompanied by CMEs. These ejections often originate in active regions, such as sunspot groupings. CMEs can be linked to other activities like eruptive prominences or solar tsunamis. These events can disrupt radio transmissions and damage electrical power grids on Earth.

A solar flare is another distinct phenomenon. It is a sudden, intense flash of brightness on the Sun's surface. A single flare can release up to 6 × 10^25 joules of energy. This is about 160 billion megatons of TNT equivalent. Flares eject clouds of ions, atoms, and electrons into space. These clouds usually reach Earth within one or two days. Flares can also cause solar proton events. These are storms of highly energetic particles that pose radiation hazards to astronauts.

Prominences are large, bright features made of gas. They often look like loops extending from the Sun's surface. These features are anchored in the photosphere and reach into the corona. Prominence plasma is much cooler and denser than the surrounding coronal plasma. A prominence can form in about one Earth day. Some can last for weeks or even months. If a prominence breaks apart, it can form a CME. The largest prominence ever recorded was over 140,000 km long.

Sunspots are dark areas found on the photosphere, the Sun's radiating surface. They appear dark because intense magnetic activity inhibits convection. This process cools the area compared to the rest of the surface. Around sunspot groups, you may find brighter areas called faculae. These occur as the flow of energy is re-established. Sunspots often appear in pairs with opposite magnetic polarity. They follow Spörer's law, which describes how their latitude declines during a solar cycle.

Humans have studied solar activity for a very long time. Records of these events date back to the eighth century BCE. In the 19th century, scientists knew very little about the Sun's energy. The 20th century brought a surge in astrophysics and new telescopes. In 1931, the invention of the coronagraph changed everything. This tool allowed scientists to study the corona even in full daylight.

Solar activity follows a periodic solar cycle lasting about 11 years.

During solar maxima, the Sun produces about three CMEs every day. During solar minima, there is only about one CME every five days. This cycle influences space weather and even Earth's climate. When a CME hits Earth, it causes a geomagnetic storm. This storm can deform Earth's magnetic field and create the aurora.

These events show how deeply our planet is connected to the Sun.