Our sun — A gigantic fireball

The probe took these excellent pictures of our sun from 77 million kilometers away. Small solar flares have never before been so clearly visible. As it gets closer to the sun, the Solar Orbiter will specifically investigate these eruptions. It will also research how solar storms — which can cause problems for us on Earth — emerge.

The sun is constantly sizzling, boiling, and erupting. The eruptions are usually small, but sometimes they can be huge. During larger solar storms, billions of tons of electromagnetically charged material are hurled into space and toward the earth. This can have consequences for us. Those eruptions can lead to power cuts or the collapse of mobile phone networks.

Our sun had already been shining for billions of years before mankind even existed. Together with the planets of our solar system, the sun developed from a gas cloud 4.6 billion years ago. And it will probably continue shining for another five billion years, until its energy reserves run out.

The sun is basically a huge nuclear fusion reactor. At its core, pressure and temperature are so high that hydrogen atoms merge together to form helium atoms. This process releases huge amounts of energy. One thimble of sun material generates as much energy as burning thousand metric tons of coal does.

Seen from Earth, the sun doesn't seem big - it is just a bright spot in the sky. But it does have a radius of about 700,000 kilometres (435,000 miles). Its core is 15 million degree Celsius (27 million degree Fahrenheit). Temperatures on the sun's surface still reach 5500 degree Celsius (10,000 degree Fahrenheit).

All stars in our universe glow because they generate energy deep down inside. Our sun is just like other billlions of stars scattered across the universe. In comparison with other stars, our sun is of medium size. Some stars are a hundred times bigger, others are just a tenth of the sun's size.

The sun's surface is seething away. Hot and brightly glowing material ascends from the sun's inside, cools and sinks down again, appearing much darker. Our sun is the only star in the universe so close to Earth that astronomers can observe in such detail.

Sometimes big dark spots appear on the sun's surface staying for about a month. Even before the birth of Christ, humans already knew of those spots, and Galileo Galilei later recorded their appearance in writing. But for a long time people were mystified where those spots came from. Now we know the answer: they're areas with a particularly strong magnetic field.

When the sun is very active, geomagnetic storms develop. It's when the sun catapults a particularly high number of charged particles into space. Those particles can hit and destroy satellites. They might also disturb electric power substations on Earth and even lead to power breakdowns.

This is another, much more beautiful effect of geomagnetic storms: an aurora, also called polar light. It occurs when charged particles of the sun hit the Earth's atmosphere. The frequency of how often we may enjoy this spectacle depends on the solar cycle. Every eleven years the sun is particularly active - that's when many geomagnetic storms and auroras can be observed.