Heliospheric Astroparticle Physics

Sun and Heliosphere

Sun Spot Cycle and Solar Activity

The sun is the largest object in the whole solar system and makes up almost 98% of the total mass. Its diameter is 109 times that of earth's, and there would be room inside it for over 1.3 million earths. The outermost visible layer is called the photosphere and has a temperature of 6000 degrees Celsius. But it's not free from flaws. Everywhere that magnetic lines go through the surface, sun spots are created. It is a region with cooler gas that looks dark against the normal photosphere. The Corona is the outermost part of the sun's atmosphere whose outer regions reach far into space. This region is called the heliosphere.

Abbildung 1: Aufnahmen von der Sonne
Image 1: Different views of the sun [original size]

A New Picture of the Sun

Life on earth without the sun is unthinkable. It gives light, warms the surface, the sea and the atmosphere, it controls the weather and climate. It gives energy for plant life and therefore all life.

The characteristics that stand out the most are the sun spots (image 1, first row left). Middle sized sunspots are already as big as the earth. The life span of a sun spot is from a few hours to a few months. Sun spots appear darker that the rest of surface because they are cooler than their surroundings. The cooling is caused by a strong local magnetic field (image 1, first row middle) and points out where there are especially intensive magnetic fields or high magnetic activity. The frequency of sunspots varies in an 11-year period, or the sun spot cycle.

Abbildung 2: Entladungen magnetischer Feldenergie (Flares)
Image 2: Discharge of magnetic field energy (flares)

Above the photosphere that is visible for the naked eye, there are other layers of the sun's atmosphere. The middle layer is called the chromosphere because of its intense color that is visible for a few seconds during a solar eclipse. The outer layer of the sun's atmosphere, the corona, is above the chromosphere and is impressive to observe during a total eclipse.
In the chromosphere, you can observe with special filters a surprisingly large variety of structures and dynamic processes, for example, prominences and the spectacular discharge of magnetic field energy (flares).

Abbildung 3: Polarlichter
Image 3: Northern lights occur mostly at times of high solar activity

After violent eruptions that release energy saved in the magnetic field, the earth can be hit with a shower of charged particles that causes interference in radio communication and, when they enter into the upper atmosphere, the northern lights.

The Heliosphere

Abbildung 4: Schematische Darstellung der Heliospähre
Image 4: Schematic model of the heliosphere

The heliosphere is described as the surroundings of the sun that is filled by expanding corona and shields us from the interstellar medium. The borders of the heliosphere have not yet been directly measured, but they lay outside of the orbits of the outer planets. Information about the heliosphere is gained though the measurements from space probes in our solar system.