How much does the earth bend the light

Moving charges in fields

The northern lights have been known since ancient times. It occurs in the form of colored ribbons, threads, flags, flames and curtains mainly in the northern latitudes, but can also be observed here. According to the myths of the Eskimos, the aurora is caused by the spirits of the deceased playing a ball game in the sky, with a walrus skull thrown back and forth producing the glow.

Another earlier idea, which at first sounds quite plausible, assumed that it is sunlight that is reflected on ice crystals in the atmosphere at altitudes of 100 to 1000 km and broken down into its components. Anders Jonas ÅNGSTRÖM (1814 - 1874) was able to refute this, as he demonstrated significant differences between the light of the aurora and sunlight. He analyzed the spectrum of the aurora and compared it with that of the sun. He came to the conclusion that many wavelengths that are represented in the solar spectrum were completely absent in the spectrum of the aurora borealis. This made it possible to rule out that the polar light is reflected sunlight.

Today we know that auroras are caused by particle radiation consisting mainly of electrons and protons, the Solar wind, is caused. This particle radiation emanating from the sun (no light) hits the earth's magnetic field and "bends" it, so that the field is pushed out to the side facing away from the sun like a comet's tail.

The Earth's magnetosphere

The darker side of the globe in the sketch represents the night side, the lighter the day side; so one looks to the evening side of the earth. The morning side is not visible because it is on the side of the earth facing away from the observer. The Bow shock wave is the region where the solar wind particles experience their first major deceleration. This causes the earth's magnetic field to be compressed on the day side of the earth. The Magnetopause is the region where the earth field and the solar wind field are approximately equally strong. The earth's magnetic field is stretched on the night side of the earth.

The LORENTZ force of the magnetic field, which results from the field of the sun and the earth's field, which is shifted by the solar wind, acts on the electrons and protons. Protons and electrons coming from the sun are deflected in different directions due to their different charges. If one were to look from the earth in the direction of the sun (and thus the oncoming particles) in the sketch, the protons would be deflected out of the plane of the paper and the electrons into the plane of the paper would be deflected. The magnetic field flowing into the far north creates a negative and a positive charge cloud. The negative charge pole is on the evening side, the positive one on the morning side. An electric field builds up in the magnetosphere between these clouds of charge, creating a kind of natural aurora generator. (Source Northern Lights page Leidmann) Since there are still individual air molecules in the magnetosphere, which are ionized by the UV radiation of the sun and the solar wind, a current flows between the two charge poles, from the morning side (+ pole) to the evening side (- Pole). This is one possibility how the magnetic field causes charge movements (referred to below as electron and proton drift) in the magnetosphere.

Furthermore, charged particles are trapped in the earth's internal magnetic field. The area in which this happens is called the Van Allen Belt and is a radiation belt of the earth. Here the electrons and protons are held like in a magnetic bottle and only reach the upper atmosphere in the vicinity of the poles. As soon as the electrons and protons get into the atmosphere, they stimulate the air molecules to glow. This usually happens at an altitude of 65km to 400km, but can sometimes be observed at an altitude of up to 1200km.

The recordings were made by the space shuttle Discovery, which was commissioned by the US Department of Defense to investigate how the northern lights can disrupt the early warning systems for ICBMs.

A space shuttle even flew through an aurora borealis once. During the crossing, the astronauts saw flashes of light, even if they kept their eyes closed. The charged particles passed through the walls of the space shuttle and the eyeball, reacted with atoms in the body and generated the lightning bolts. (Source: fh-wiesbaden)

Those looking for more pictures and additional information can find them on the University of California's Aurora page.