Its diameter is about 30 Earth radii, and outside of the magnetosphere is the solar wind. The magneto-sphere is the region of space around Earth that is controlled by Earth’s magnetic field. Large-scale structures, like multiple parallel arcs (Figures 4-5) and spirals that fill almost the entire sky (Figure 6) show the spatial pattern of these currents. This region is connected to the outer magnetosphere by electric currents. The smaller scale structures like rays, small curls, and thin curtains shown in Figure 3 represent structures in the acceleration processes. Following the magnetic field up from the aurora, we get to the auroral acceleration region, about 620-6,200 miles (1,000-10,000 km) above the earth. This shapes the aurora into curtain and ray-like structures (Figure 2). We can model the aurora and are now gaining the understanding to forecast its appearance (Lummerzheim 2007).Ĭharged particles, like those that cause the aurora, can generally only travel along the direction of the magnetic field. But we do have a fairly good understanding of the general processes and the flow of energy that feeds these processes. These energetic particles come from the volume of space just above the aurora, and are accelerated by plasma physics processes that are still under investigation. The light of the aurora is generated by atoms and molecules of the air when they are struck with energetic particles from space. Note comet Hale-Bopp in the lower right hand corner. Several parallel curtains above Rock Creek in Denali National Park and Preserve. The peoples who lived at high latitude and who had a regular display of the aurora held similar beliefs.įigure 5. In ancient times when the aurora appeared overhead, people often associated the aurora with good or bad omens and sometimes considered it a manifestation of activities of heavenly spirits or gods.
Aurora is visible at mid-latitudes during the largest magnetic storms, but it is dominated by red colors. Although the native people from New Zealand must have seen aurora on occasion, Captain Cook is considered the discoverer of the aurora australis he saw it in 1773 on his voyage around the southern tip of South America.Īt mid-latitudes, people rarely see the northern lights. The term aurora borealis originated in the 1600s, when Galileo combined the word “aurora,” the Latin word for “dawn,” with the term “boreal,” the Greek word for “north.” Aurora also appears in the southern hemisphere, where it is called the “aurora australis.” Since there is very little populated landmass at high southern latitudes, there are no known historical and mythological references to the southern aurora. This structure is related to the auroral acceleration process directly above the atmosphere. Small-scale structure in aurora shows as thin curtains and small rays and curls over Fairbanks, Alaska. The author wrote the book to prepare Norwegian King Magnus Lagabøte for his duties as a ruler.įigure 3. The first recorded use of the words “northern lights” to describe the aurora was in 1230, in a book titled The King’s Mirror. In his book Majestic Lights, Eather (1980) presents several quotes from the Bible that most likely refer to aurora. 2,300 years ago, Aristotle saw curtains of light in the sky and called the phenomena “chasmata” to indicate that the cause was cracks in the sky, allowing in light from beyond the heavenly sphere. High-resolution spectral observations let us understand how the upper atmosphere is affected by auroraĪ Brief History of Understanding the Auroraĭescriptions of aurora, or the northern lights, go as far back as written history. Observations of color balance in aurora can provide us with information about the physical processes in the near Earth space that cause aurora. This article discusses the mechanisms that are responsible for the colors of the aurora. The aurora has fascinated observers at high latitudes for centuries, but only recently have we begun to understand the processes that cause it.
Green curtains and rays above the Brooks Range and Gates of the Arctic National Park.
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