Earth's Magnetic Field
Areas where an object shows magnetic influence are called magnetic fields. The effect occurs along magnetic field lines. English scientists Michael Faraday and James Clerk Maxwell discovered the concepts of magnetic field and magnetic lines. Earth's magnetic field is also called the geomagnetic field.
The Earth's magnetic field reaches out into space and meets the solar wind. The solar wind contains charged particles coming from the Sun. The Earth's magnetic field deflects the solar wind which can break down the ozone layer protecting the Earth from ultraviolet radiation.
The magnetic field also deflects cosmic rays from outside the solar system. These are high-energy charged particles. They are kept out of the solar system by the Sun's magnetosphere. A magnetosphere is an area around a planet or other astronomical object where charged particles are manipulated. The magnetosphere occurs because the planetary object has hot metallic cores.
The solar wind exerts a pressure which if it reached all the way to the Earth's atmosphere, would erode it. However, Earth's magnetic field exerts pressure back and stops the dangerous solar wind. Even the Earth's magnetic field cannot completely stop the charged particles from entering the magnetosphere. These particles bounce back and forth between the poles. A ring current is formed when positive ions go westward, and negative ions go eastward. The magnetic field at the Earth's surface is reduced because of that ring current.
Space weather occurs in the magnetosphere. Conditions in the magnetosphere change. This is caused by solar activity. The magnetosphere gets bigger if the solar wind is weak. If the solar wind is strong, more of it penetrates the compressed magnetosphere. Geomagnetic storms can occur when shock waves are sent through the solar system from eruptions above the Sun or solar flares. A shock wave of this type can reach the Earth in two days. It can cause damage to the satellites in the atmosphere. The largest geomagnetic storm was recorded in 1859. It shorted out telegraph lines.
In 1832, Carl Friederic Gauss measured the Earth's magnetic field. It has been measured continuously over the last one hundred years. The field has decayed about ten percent in that time. Governments sometimes operate geomagnetic observatories which measure the Earth's magnetic field. They can forecast magnetic conditions. These could be storms which would affect electric power and communications. One hundred geomagnetic observatories are connected in the International Real-time Magnetic Observatory Network. It has been measuring the Earth's magnetic field since 1991. The military use geomagnetic measurements to detect significant metallic objects, like a submarine under water.
An interesting fact is that during migration some animals, including birds and turtles, can navigate because they can detect the Earth's magnetic field. Some scientists believe that wild deer and cows, when they are not under high voltage power lines, usually align their bodies north-south when they relax. The scientists suggest that magnetism is the cause. Other scientists disagree with that finding.
European robins and some other songbirds use a magnetic compass to navigate the Earth's magnetic field. Very weak electromagnetic fields can disrupt the compass. Scientists put the blame for this occurrence on AM radio signals and other electronic equipment found in homes or businesses.
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