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The photos we usually see portray aurorae in a kaleidoscopic range of
colors. So why was the aurora we encountered in step 3 red?
The basic colors of the aurora are green and pink. The electrons
accelerated by the action of the solar wind and the Earth's magnetic field
collide with the air (which consists chiefly of oxygen and nitrogen),
separating the electrons from their the atoms somewhat. This process is
called excitation. When the excited electron, which had been circling the
outer perimeter of the atom, rejoins the its original orbit in the atom,
this surplus energy is released. This energy is visible as luminescence,
and its properties vary depending on the element. The light emitted from
oxygen atoms is generally green or dark red, while that of nitrogen
molecules is pink. Hence the basic colors of the aurora are green and pink.
This is how we know that the aurora observed at Rikubetsu-cho in Hokkaido
was created by the luminescence of oxygen atoms.
We can demonstrate that each element has its own characteristic color in an
experiment known as the "flame reaction." In this reaction, solutions of
different elements are heated to energize the atoms. The electrons are
excited (moved to the a higher orbit in the atom), then differences are
observed in the color of the light generated when the electrons return to
their original orbits. By comparing the colors with those in the photo
below, try to guess which type of atom the light is generated by.
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