The aurora has fascinated observers at high latitudes for centuries, but only recently have we begun to understand the processes that cause it. This article discusses the mechanisms that are responsible for the colors of the aurora. Observations of color balance in aurora can provide us with information about the physical processes in the near Earth space that cause aurora. High-resolution spectral observations let us understand how the upper atmosphere is affected by aurora
At mid-latitudes, people rarely see the northern lights. Aurora is visible at mid-latitudes during the largest magnetic storms, but it is dominated by red colors. 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. The peoples who lived at high latitude and who had a regular display of the aurora held similar beliefs.
What causes the colors in the aurora borealis
When an atom or molecule emits light as a photon, to rid itself of its excess energy, that photon has a wavelength that is characteristic for that atom. We perceive wavelength as color. Laboratory experiments can reproduce these light-emitting processes by forcing a current through an evacuated glass tube that contains a small amount of a selected gas. The study of these light-emitting processes led to the understanding of atoms early in the twentieth century, and to the discovery of quantum mechanics. Because each type of atom or molecule emits colors unique to it, we can use the colors of the aurora to determine the atmospheric composition at the auroral altitude.
However, the auroral electrons sometimes have enough energy to give them the punch to penetrate deeper than that into the atmosphere. When that happens, only emissions with a much shorter lifetime are possible. The most abundant gas is molecular nitrogen, and it radiates promptly in deep blue and red colors. Mixing these together gives purple. The bottom edge of a green auroral curtain gets this purple color when auroral elec-trons are accelerated to very high energy (Figures 7-8).
The observations of the colors of the aurora, either in a broader sense by looking at the overall color balance, or by detailed spectroscopic methods, can teach us much about the physical processes that cause aurora and the effects that aurora has on the upper atmosphere. The color balance tells us the altitude of aurora. We can relate that to the processes that accelerate auroral electrons in the near earth space, and we can see the evolution of electric currents that flow in the magnetosphere. High-resolution spectroscopy lets us see the wind in the upper atmosphere and how it is changed by the aurora. High altitude blue aurora tells us that ions that are generated in the aurora are pulled out of the atmosphere into space. And the colors themselves tell us the composition of the atmospheric gas at the altitude of the aurora.
The bright dancing lights of the aurora are actually collisions between electrically charged particles from the sun that enter the earth's atmosphere. The lights are seen above the magnetic poles of the northern and southern hemispheres. They are known as 'Aurora borealis' in the north and 'Aurora australis' in the south.. Auroral displays appear in many colours although pale green and pink are the most common. Shades of red, yellow, green, blue, and violet have been reported. The lights appear in many forms from patches or scattered clouds of light to streamers, arcs, rippling curtains or shooting rays that light up the sky with an eerie glow.
Northern Lights can be seen in the northern or southern hemisphere, in an irregularly shaped oval centred over each magnetic pole. The lights are known as 'Aurora borealis' in the north and 'Aurora australis' in the south. Scientists have learned that in most instances northern and southern auroras are mirror-like images that occur at the same time, with similar shapes and colors.
'Aurora borealis', the lights of the northern hemisphere, means 'dawn of the north'. 'Aurora australis' means 'dawn of the south'. In Roman myths, Aurora was the goddess of the dawn. \par Many cultural groups have legends about the lights. In medieval times, the occurrences of auroral displays were seen as harbingers of war or famine. The Maori of New Zealand shared a belief with many northern people of Europe and North America that the lights were reflections from torches or campfires.
The Aurora Borealis is most often seen in a striking green color, but it also occasionally shows off its many colors ranging from red to pink, blue to purple, dark to light. The reason that the aurora is seen in so many colors is that our atmosphere is made up of many different compounds like Oxygen and Nitrogen. When the charged particles that come from the sun hit the atoms and molecules of the Earth's atmosphere, they excite those atoms, giving off light. Different atoms give off different colors of the spectrum when they are excited. A familiar example is the Neon lights that we see on many business signs in our modern world. The Neon lights contain the gas Neon. These lights have electricity run through them to excite the Neon gas. When the Neon is excited, it gives off a brilliant red-orange color. The Neon lights are the same idea as the aurora, only on a lot smaller scale.
To use your device for capturing aurora borealis, you need to be able to adjust the manual settings on your camera. This means if the standard app on your phone/tablet doesn't allow you to do this, you'll need to find another option. The best camera app option by far is from Adobe.
Dawn WindThe aurora borealis, or northern lights, was studied by ancient Roman and Greek astronomers. The phenomenon was named for the Roman goddess of the dawn, Aurora, and the Greek god of the north wind, Boreas.
Fox FireIn Finland, the aurora borealis is called revontulet, which literally translates to fox fires. According to one Finnish folk tale, the lights are caused by a magical fox sweeping his tail across the snow and sending sparks up into the sky.
Polar lights (aurora polaris) are a natural phenomenon found in both the northern and southern hemispheres that can be truly awe inspiring. Northern lights are also called by their scientific name, aurora borealis, and southern lights are called aurora australis.
The northern lights, or aurora borealis, are a spectacular, colourful display of light commonly seen in the night sky in the northern hemisphere. Auroras in the southern hemisphere are known as the southern lights, or aurora australis.
The word "aurora" is derived from the name of the Roman goddess of the dawn, Aurora, who travelled from east to west announcing the coming of the sun.[4] Ancient Greek poets used the corresponding name Eos metaphorically to refer to dawn, often mentioning its play of colors across the otherwise dark sky (e.g., "rosy-fingered dawn").[5]
In northern latitudes, the effect is known as the aurora borealis or the northern lights. The former term was coined by Galileo in 1619, from the Roman goddess of the dawn and the Greek name for the north wind.[11][12] The southern counterpart, the aurora australis or the southern lights, has features almost identical to the aurora borealis and changes simultaneously with changes in the northern auroral zone.[13] The aurora australis is visible from high southern latitudes in Antarctica, Chile, Argentina, South Africa, New Zealand and Australia. The aurora borealis is visible from being close to the center of the Arctic Circle such as Alaska, the Canadian Territories, Iceland, Greenland, Norway, Sweden, Finland and Russia. On rare occasions the aurora borealis can be seen further south, for example in Estonia, Latvia, Lithuania, Scotland, Ireland, Denmark, and the northern part of the contiguous United States.
In 2016, more than fifty citizen science observations described what was to them an unknown type of aurora which they named "STEVE", for "Strong Thermal Emission Velocity Enhancement". STEVE is not an aurora but is caused by a 25 km (16 mi) wide ribbon of hot plasma at an altitude of 450 km (280 mi), with a temperature of 6,000 K (5,730 C; 10,340 F) and flowing at a speed of 6 km/s (3.7 mi/s) (compared to 10 m/s (33 ft/s) outside the ribbon).[34]
The effect of the aurorae on the electric telegraph is generally to increase or diminish the electric current generated in working the wires. Sometimes it entirely neutralizes them, so that, in effect, no fluid [current] is discoverable in them. The aurora borealis seems to be composed of a mass of electric matter, resembling in every respect, that generated by the electric galvanic battery. The currents from it change coming on the wires, and then disappear the mass of the aurora rolls from the horizon to the zenith.[74]
The earliest datable record of an aurora was recorded in the Bamboo Annals, a historical chronicle of the history of ancient China, in 977 or 957 BCE.[75]An aurora was described by the Greek explorer Pytheas in the 4th century BC.[76] Seneca wrote about auroras in the first book of his Naturales Quaestiones, classifying them, for instance, as pithaei ('barrel-like'); chasmata ('chasm'); pogoniae ('bearded'); cyparissae ('like cypress trees'); and describing their manifold colors. He wrote about whether they were above or below the clouds, and recalled that under Tiberius, an aurora formed above the port city of Ostia that was so intense and red that a cohort of the army, stationed nearby for fire duty, galloped to the rescue.[77] It has been suggested that Pliny the Elder depicted the aurora borealis in his Natural History, when he refers to trabes, chasma, 'falling red flames', and 'daylight in the night'.[78]
The northern lights (aurora borealis) illuminate the sky over Reinfjorden in Reine, on Lofoten Islands in the Arctic Circle in 2017. Jonathan Nackstrand/AFP via Getty Images hide caption 2ff7e9595c
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