An aurora, or 'polar light', is a natural light display in the sky. They are usually seen in the high latitudes (Arctic and Antarctic) regions. Auroras are produced when the Earth's magnetosphere is disturbed by the solar wind.
An aurora around the North Pole is called Aurora borealis or 'northern lights'. Around the South Pole it is Aurora australis or 'dawn of the south'. It can be seen from long distances, stretching in the sky many hundreds of miles.
Auroras can only be seen at night because their light is not as strong as the light of day. For instance, faint stars can be seen through the aurora. However they do happen during the day as well.
Aurora occurs when the Sun sends off particles into space. These particles are mainly electrons, with charge and energy, which means they contribute to electricity. Earth has a protective shield of energy around it. This is called the "magnetic field" and forms an elongated sphere around the Earth called the "magnetosphere". The Earth’s magnetic field wards off most of the solar wind.
At high-latitude areas (polar areas), the magnetic field is vertical. It does not ward off particles of the solar wind and can come from the magnetosphere and hit the particles of the air (Earth's atmosphere). When they hit, the atmosphere is heated and excited and the excess energy gets away, a phenomenon which we see as moving lights in the sky above 100 km altitude typically. An aurora can be especially bright following a solar event called a coronal mass ejection (CME), when the charged particles rip through the electromagnetic field because of their power.
Auroral phenomena have been observed on other planets than Earth that have a magnetic field, such as Jupiter, Saturn and more recently Mars. It is believed to be a widespread phenomenon in the Solar System and beyond.
Many legends are associated with the aurora, in all countries where this phenomenon regularly occurs.
References[change | change source]
- McIlwain C.E. 1960. Direct measurement of particles producing visible auroras. Journal of Geophysical Research. 65: 2727.