Magnetic Fields: From the Sun

It’s not just the planets that have magnetic fields. The Sun also has a very large and dynamic magnetic field.

The sun’s magnetic field is formed much like on Earth and Jupiter. There are convection cells that bring heat from the sun’s heat sources to the surface. These convection cells, and the sun’s rotation period of 25.4 Earth days produce the sun’s magnetic fields. However, there are many notable differences.

These granules on the sun are convection cells.

The sun is over 12,000 times larger than the Earth, which means that its magnetic fields are larger as well. It’s so large, it extends past the orbit of Pluto. However, it isn’t a solid object, like Earth. The sun’s material is mostly plasma, which works like a gas; like Jupiter. This means that the sun experiences differential rotation, where the equator rotates faster than the poles. On the sun, its Equator rotates every 25.4 days, but its poles rotate every 29 days. This video will demonstrate what that does to the sun.
When the sun rotates, the equator stretchs the magnetic field lines towards the sun’s direction of rotation, and it will keep stretching it until they snap like rubber bands. When they snap, they release the energy in the magnetic field and the magnetic field lines pop out of the sun. These magnetic field lines cause the charged particles from the surface to become trapped along the magnetic field lines. Those trapped particles are called prominences. In addition, Sunspots are formed where the magnetic field lines poke out and in, when the charged particles are lifted from its surface. That is why sunspots are common during periods of high solar activity, like the Solar Maximum.

Eventually, the magnetic field lines will reconnect with each other, and release a lot of energy, leading to large solar flares, and coronal mass ejections. At the same time, the polarity of the magnetic fields will reverse. When the flip is complete, the sun’s magnetic field will drop to zero, reappear in its reversed polarity, and start the process again. This process occurs every 11 years and after each cycle, the poles reverse.

Today, there is evidence that the Sun’s magnetic field is in the process of flipping after a chaotic solar maximum. Once the flip is complete, the process starts again.

Here is a video that talks about the sun and its solar cycle by NASA:



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Coursera Lecture 6.6





Magnetic Fields: Its Purpose on Earth

Hi everybody,

If you have used a compass, then you have used one of Earth’s key features to find your way. That feature is Earth’s magnetic field.

Earth is a giant magnet. This is because the core generates the magnetic field using the process called the geodynamo. The geodynamo process works like this: the outer core is full of conductive metals that is heated from below by the inner core. This drives the convection. The convection in the outer core is maintained by the heat in the inner core, and chemical differentiation. With help by the rotation of the Earth, this drives convection, and creates an instability that forms the magnetic field, and this process aligns the magnetic field to the rotational axis of the planet.

The Geodynamo Process

Magnetic fields are essential for life on Earth. That is because the magnetic field protects the planet from cosmic rays and charged particles from solar flares. When the charged particles hit the magnetic field, they become trapped and slide along the field lines moving towards the poles. The strongest areas of the magnetic field are near the poles, and if the particles are not strong enough, then they are repelled and they bounce back and forth along the field lines and that creates the Van Allen Radiation Belts. There, the magnetic field has trapped the charged particles to prevent them from reaching the atmosphere. If we didn’t have the magnetic field protecting the Earth, then the atmosphere would become stripped of its atoms and the radiation from the solar wind would irradiate all life on Earth.

Van Allen Radiation Belts

However, the charged particles also interact with the magnetic fields. The motions of charged particles in circles form magnetic fields of their own. As a result, when both magnetic fields collide with each other, Earth’s magnetic field absorbs the momentum of the charged particles, and that pushes Earth’s magnetic field back. The Earth wants to make an even magnetic field, but the Sun is pushing the magnetic fields away from the sun. It’s not an even bombardment, due to the variations in solar output.

There are times when the solar wind is strong enough to overcome the magnetic field. The charged particle slides along the field into the poles, and when it is strong enough, it enters the atmosphere near the Earth’s poles, and ionizes the atmosphere. This leads to a beautiful sight called the Aurora Borealis/Australis.

Auroras over the landscape

Earth is not the only planet with a magnetic field though.

Stay tuned for my next post.



Coursera Lecture – Week 5.8