-
Asked by maddiet to Mark, Matthew, Mike, Paul, Sabina on 10 Mar 2014. This question was also asked by 10216mw, .
-
Paul Coxon answered on 10 Mar 2014:
The Northern Lights work by a similar mechanism as neon lights used in advertising. They involve an interaction between charged particles and the Earth’s magnetic field.
The Sun isn’t a uniformly stable object – in undergoes periods of high and low activity. Occasionally during a period of high activity it will emit a burst of charged electrons and protons called plasma during an event called a coronal mass ejection. The solar wind produced by the Sun spreads these charged particles throughout our solar system and towards Earth.
The plasma eventually reaches Earth’s magnetosphere – the magnetic shield surrounding Earth to protect us from the dangerous particles and radiation in space. The magnetosphere isn’t perfectly spherical – the solar wind is always pushing against it, deforming and stretching it into a long leeward tail like the wake of a ship, which is called the magnetotail.
Most of these particles are diverted away from Earth, but some end up being trapped in the magnetotail, and directed along the field lines, becoming more dense near the magnetic poles. These charged particles are propelled into the upper reaches of the atmosphere – the ionosphere, and collide violently with the neutral gas atoms up there. These collisions transfer energy to the gas atoms. The collisions cause the electrons of the atmospheric atoms to become excited. As the electrons return to their original energy levels, these atoms emit visible light of distinct wavelengths, to create the colours of the aurora and making the ionosphere glow!
The different colours in an aurora depends on the wavelength of the light emitted. This is determined by the specific proportions of gases in the atmosphere and and the energy of the particle hitting it.
Above 300 km the ionosphere is mostly oxygen which when excited gives out a red glow. Other gases at lower levels such as nitrogen and helium produce blue or purple.The Northern Lights were recently seen in the skies above the UK, and the photos taken on those nights were really spectacular. Unfortunately they couldn’t be seen in Cambridge and I’m very sad to have missed them 🙁
-
-
Mike Lee answered on 10 Mar 2014:
The sun is like a huge explosion, held together by it’s shear size. Nonetheless, very dangerous particles are being thrown out all the time. By good fortune, the Earth as a magnetic field, which literally is a shield against these particles. If we didn’t have one, life on Earth would not survive.
Sometimes, after a large explosion on the sun, the magnetic field breaks and these particles make it to the atmosphere. They hit into the air, making the it glow in different colours.
-
Matthew Malek answered on 11 Mar 2014:
“Northern Lights” is a 1995 novel by Phillip Pullman, set in a fictional alternate version of my home town, Oxford. When published in the USA, the name was changed to “The Golden Compass”. They also made a horrible film version in 2007.
😀
Seriously, though, the northern lights, or an “aurora borealis” is caused by a massive ejection of charged particles from the Sun. These particles are primarily protons, like the solar wind, but there are also some electrons, too.
The Earth has a magnetic field, and charged particles bend their path in a magnetic field. So the Earth’s magnetic field guides these solar particles towards the North pole. (Also the South pole, but you won’t get “northern” lights down there!) These particles excite electrons in the atmosphere, which then de-excite back to their original “ground state”, giving off the extra energy in the form of the beautiful coloured lights.
When you see green or brownish red light, you can tell your friends that this is coming from oxygen. If you see blue or red light, the emission came from oxygen. Those are the two major components of the Earth’s atmosphere.
Meanwhile, the Southern lights (or “aurora australis”) happen in the Southern skies by exactly the same process… and usually at the same time as the Northern lights. Since the original trigger was activity in the Sun, it happens for both at once.
-
Mark Jackson answered on 12 Mar 2014:
In Roman myths Aurora was the goddess of the dawn, so ‘Aurora borealis,’ the lights of the northern hemisphere, means ‘dawn of the north’. 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.
We’re a little more scientific about things today. The Northern Lights are actually the result of collisions between gaseous particles in the Earth’s atmosphere with charged particles released from the sun’s atmosphere. Variations in colour are due to the type of gas particles that are colliding. The most common auroral color, a pale yellowish-green, is produced by oxygen molecules located about 60 miles above the earth. Rare, all-red auroras are produced by high-altitude oxygen, at heights of up to 200 miles. Nitrogen produces blue or purplish-red aurora.
Comments
maddiet commented on :
Thank you!