Northern light, Aurora borealis in Kirkjufell in Iceland.
How Aurora is produced
The Sun is the closest star to us at 93 million miles. Despite this huge distance, the pure energy from the Sun is strong enough to warm our world and sustain life. The Sun constantly emits a stream of radiation called the solar wind. The solar wind is made up of countless particles that have been charged with large amounts of energy by the Sun. These high-energy particles are deadly to life on Earth and can damage the very structure of our DNA. Fortunately, the Earth has developed natural barriers that protect us from the solar wind. The Earth’s magnetic field is our main form of defense against the solar wind. This field is generated because the Earth has a rotating iron core. Iron can carry electricity and as it rotates, the moving electric charge creates a magnetic field. The magnetic field generated by the Earth’s core moves outward and forms a web-like structure that encloses our universe. When the solar wind meets the Earth’s magnetic field, it redirects away from our world. Without a magnetic field, the solar wind would slowly erode our atmosphere until nothing but a thin veil of air remained. Solar wind illustration However, not all particles are redirected to the solar wind. Instead, the magnetic field redirects certain charged particles to the Earth’s poles. Even when the solar wind manages to reach our world, life is still protected by an ozone layer. However, there are two major holes in the Earth’s ozone, one at each pole. When charged particles are redirected to the North and South Poles, they interact with atoms in our atmosphere. The amount of energy in the solar wind causes some of the atoms in the Earth’s atmosphere to lose their electrons, a process called ionization. With the ionization of the particles in our atmosphere, the solar wind forces them to release beams of light with high energy. The lights are simply ionized atoms in our atmosphere that have interacted with charged particles from the Sun, forcing them to glow and move in the air.
The Many Colors of the Saddle
Aurora Borealis in Iceland
Although the saddles are generally green, they can come in many different colors. The color of the saddle is determined by the atoms ionized longitudinally and the altitude at which it occurs. Since oxygen and nitrogen are the most abundant chemicals in the Earth’s atmosphere, the colors of the saddle are determined by how these two chemicals interact with the solar wind. When oxygen is ionized at high altitudes, the saddle glows red. At lower altitudes, ionized oxygen is green. The reason why the same chemical can emit two different colors has to do with the fact that at higher altitudes, the oxygen density is much lower than at lower altitudes. The high altitude allows the solar wind to ionize oxygen at a higher frequency and produce a red glow. Similarly, at lower altitudes the frequency with which the solar wind interacts with oxygen is lower and the product is green light. In addition to red and green, the saddle can be blue or purple. If you happen to see these two colors, it means that nitrogen is ionized in the atmosphere. The process by which the saddle forms and produces its exceptional colors only adds to their beauty and complexity.
Aidan Remple April 12, 2022 in Science
