Question

What are auroras and how do auroras form?

Answer 1

Auroras are the beautiful curtains of light in the night skies of the far north and south. In the Northern Hemisphere, they are popularly called Northern lights, and officially known as "Aurora Borealis" (meaning "northern dawn"); in the Southern Hemisphere, they are known as "Aurora Australis" or the Southern Lights.
During the luminous phenomenon of an Aurora, streams of colourful light appear as reds, greens, yellows, pinks, and purples. Most of the spectacular displays can be divided into one of three dominant forms. In the first form, a homogenous band or arc of light rises across the lower part of the sky from east to west, reaching within a few degrees of the horizon. This band may be just 100 m thick. In the second form, rays stream up vertically from the arc or band-like fringes on fine fabric, following the lines of the Earth’s magnetic field. A third form, the corona, is seen when the aurora is directly above you, and rays seem to fall around you from the zenith of the sky. A single auroral display may incorporate a range of these forms and a variety of colours, depending on the composition of the atmosphere. Auroral arcs can stand almost still and then, as though a hand has been run along a tall curtain, begin to dance and turn. After midnight, the aurora can take on a patchy appearance, and the patches often blink on and off once every 10 seconds or so until dawn.
Essentially, the light of auroras is emitted when charged particles in the solar wind excite the electrons of atmospheric atoms through collisions. As the electrons return to their original energy levels, these atoms, primarily oxygen and nitrogen, emit photons of visible light of distinct wavelengths to create the colours of the auroral display. The wavelength of the light depends upon the electronic structure of the atoms or molecules themselves, and on the energy of the charged particle colliding with the atom or molecule.