The Sun.

Our Sun.

Here I intend to describe what it's on the Sun that influences the Earth to make an aurora develop.

Sunspots.

Sunspots are dark spots in the solar photosphere (Sun's visible surface), which can have a diameter of 2,000-100,000 km. The sunspot consists of a dark interior, the umbra with a temperature 2000 - 2500 degrees lower than the photosphere's 5800 °K. The umbra is sometimes surrounded by a lighter area known as the penumbra and its temperature is about 500 degrees lower than the photosphere's. A sunspot suddenly appears as a dark poor and grows in size until it covers a larger or smaller part of the photosphere, it can divide into smaller groups of spots or disappear after a couple of weeks or months. Very large sunspots, or groups of sunspots, often have longer duration The sunspots vary periodically in numbers with a cycle of eleven years. This variation is called the solar cycle. The latest maximum occurred in February 2014. The long awaited solar cycle 25 arrived early November 2019. Solar cycle max is expected around the year 2023 or 2024.

Take a look at the sharpest picture ever made of a sunspot. Picture made with the Swedish solar telescope at La Palma.

Solar flares.

The most violent events on the Sun are the solar flares, which occur near the sunspots. When a solar flare is discharged, a sudden release of energy appearing as electromagnetic radiation on all wavelengths is spread out. Solar flares are very intense radio wave transmitters, and on the Earth we receive radiation many times stronger than from any other cosmical radio source. A plasma cloud consisting of electrons and protons, a CME (Coronal Mass Ejection), is eventually thrown out into the solar wind with a speed up to 2000 km per s. The solar wind which normally has a speed of 300 - 400 km per s increases in intensity and when it reaches the Earth, after a couple of days, magnetic disturbances and aurora occur on the Earth.

Corona holes.

Where the Sun's magnetic field is open and allow particles, mostly electrons and protons to escape freely into the solar wind and travel through the solar system is called a coronal hole. The velocity of the solar wind increases and when the intensified solar wind reaches the Earth it interacts with the Earth's magnetic field and aurora occur. Corona holes with a position that influences the Earth are most common at the end of the solar cycle.