Just had to show you this stunning picture of the Aurora Australis, the one that appears over the Southern hemisphere, as opposed to the Aurora Borealis, which is visible from the Northern hemisphere. It was taken by astronauts aboard the International Space Station (ISS), and shows the aurora australis against the backdrop of Earth's horizon.
The ISS was over the Southern Indian Ocean at an altitude of 350 km, with the astronauts looking towards Antarctica and the South Pole. Dense cloud cover is dimly visible below the aurora. The curvature of the Earth’s horizon can be clearly seen as well as the faint blue line of the upper atmosphere.
The stunning sight is formed as charged particles streaming from the Sun – known as the solar wind - interact with Earth’s magnetic field, resulting in collisions with atoms of oxygen and nitrogen in the upper atmosphere. This striking aurora image was taken during a geomagnetic storm that was probably caused by a coronal mass ejection from the Sun on May 24th. The atoms emit photons as a means of returning to their original energy state. The photons form the aurora that we see.
The most commonly observed colour of aurora is green, caused by photons (light) emitted by excited oxygen atoms at wavelengths centered at 0.558 micrometers, or millionths of a metre. Visible light is reflected from healthy (green) plant leaves at approximately the same wavelength. Red aurora are generated by light emitted at a longer wavelength (0.630 micrometers), and other colours such as blue and purple are also sometimes observed.
While aurora are generally only visible close to the poles, severe magnetic storms impacting the Earth’s magnetic field can sometimes shift them towards the equator.