Discover the Fascinating Phenomenon of Northern Lights

[gem0688]

Hi,

I have allways loved the look of the northern lights, but have never quite understood what actually causes them!

Could anyone possibly explain it to me?

Thanx

 

[EL]

Try this one:
http://en.wikipedia.org/wiki/Aurora_(astronomy)

Please ask if there's something you think is hard to understand.

 

[gem0688]

Ok , i understand a bit, but i am still a bit confused.

They are caused by electrons of a certain energy which collide with atoms. Yes or no? And then how are the colours produced?

Thanx

 

[Hootenanny]

They are caused by electrons of a certain energy which collide with atoms. Yes or no? And then how are the colours produced?

Have you heard about quantum physics? Light spectroscopy for example?

~H

 

[gem0688]

yea, i did quantum physics a few years ago so a bit rusty! (all that photeletric effect and E=hf. Yea?!)

 

[Hootenanny]

yea, i did quantum physics a few years ago so a bit rusty! (all that photeletric effect and E=hf. Yea?!)

Yep, the formula you gave, $E = hf$ is important here. Now if there are free electrons in the atmosphere, what would happen if one of these electrons were to collide inelastically with an electron of, say an oxygen atom in the atmosphere?

~H

 

[gem0688]

Yep, the formula you gave, $E = hf$ is important here. Now if there are free electrons in the atmosphere, what would happen if one of these electrons were to collide inelastically with an electron of, say an oxygen atom in the atmosphere?

~H

Ok, well in an inelastic collision part of the kinetic energy will be changed to other forms of energy and so the electron will slow down. If it was to collide with an oxygen atom, the oxygen's electrons will become excited and so realease energy as light.

Ohhh i think i am getting there now. So then the colour of light will depend on the energy, frequency (because of E=hf) and the atom it has just collided with?

Still confused though on what makes them move around?

 

[Hootenanny]

the oxygen's electrons will become excited and so realease energy as light.

Almost there, they will release energy when they drop back down energy levels.

So then the colour of light will depend on the energy, frequency (because of E=hf) and the atom it has just collided with?

It will depend on the difference between the energy levels.

The aura of the northern lights is caused by the solar winds (a stream of plasma carrying ionised positve ions and electrons), they interact with the Earth's magnetic field.

~H

 

[gem0688]

Ok, I was nearly there!

so does the colour of light emmited depend on how big the drop back down between energy levels? Does it also depend on how high the collision takes place?

So they seem to 'dance' in the sky because the Earth's magnetic field generated by the Earth's core interacts with the solar winds which pulls thems in different directions?

Thanx again

 

[Hootenanny]

so does the colour of light emmited depend on how big the drop back down between energy levels? Does it also depend on how high the collision takes place?

Yes and yes. RE the second point, I'm not sure why this happens, perhaps do to the different composition of the atmosphere at different altitudes.

So they seem to 'dance' in the sky because the Earth's magnetic field generated by the Earth's core interacts with the solar winds which pulls thems in different directions?

From thinkquest;
"As the wind is thrown thousands of kilometers out into space where it later collides with the Earth's magnetic field, it will produce a powerful force while buffeting and distorting the shape of the Earth's field. The gusts of the solar wind and the ripples they cause in the Earth's magnetic field lead to the common brightening, fading, and dancing of the northern lights. Therefore, the greater the solar wind is, the more active the lights will be."

~H

 

[scott1]

Isn't the Northen also caused by how the Earth is titled and the angle of light?

 

[gem0688]

Yes and yes. RE the second point, I'm not sure why this happens, perhaps do to the different composition of the atmosphere at different altitudes.

~H

Ohh ok, so it all depends with what it is colliding with at different levels. So for example, at a lower level there may more oxygen collisions compared to another part.

I think i am getting there at last!

 

[gem0688]

Isn't the Northen also caused by how the Earth is titled and the angle of light?

Would this be beacuse of the light gets split up when it hits parts of the Earth's atmosphere at different angles?

 

[scott1]

Would this be beacuse of the light gets split up when it hits parts of the Earth's atmosphere at different angles?

It might but I'am not sure.

 

[Labguy]

Would this be beacuse of the light gets split up when it hits parts of the Earth's atmosphere at different angles?

The most "favorable" times of year is explained http://science.nasa.gov/headlines/y2001/ast26oct_1.htm" .

Ant http://www.atoptics.co.uk/" is cool for about every other type of atmospheric phenonenom.

 

[gem0688]

The most "favorable" times of year is explained http://science.nasa.gov/headlines/y2001/ast26oct_1.htm" .

Thanx, had a look at that site, was good. The pictures of the northern lights are really good. Also found the animation of how the magnetosphere is squashed helpful.

So it is because the electrons escape from the magnetosphere into our atmosphere, where the collisions with atoms occur.

Thanx

 

[gem0688]

ohhh and the collisions cause energy to be released when they drop back down energy levels, which causes the colour! ;)

 

[Schrodinger's Dog]

The colour is due to the composition of gases in the atmosphere, the green yellowish hues come from the emission spectrum of oxygen where as the blues and reds are the result of the emission spectrums of Nitrogen ions.

 

[gem0688]

Ohh now i see, so each different gas gives off a different colour.

Thnx Schrödinger's Dog

Gema

 

[BornLogician79]

When I first thought about the northern lights, for some reason I was under the impression that it was gravity deflecting light relative to how a prism bends/divides light, in combination with the gas difference. Gravity of north pole deflect (c) and gas breaks light up?
Very nice display!

 

[EL]

When I first thought about the northern lights, for some reason I was under the impression that it was gravity deflecting light relative to how a prism bends/divides light, in combination with the gas difference. Gravity of north pole deflect (c) and gas breaks light up?
Very nice display!

The infuence from the Earth's gravitational field on light is extremely tiny.

 

[Michael Mozina]

Ohh ok, so it all depends with what it is colliding with at different levels. So for example, at a lower level there may more oxygen collisions compared to another part.

I think i am getting there at last!

You do have the idea. Keep in mind that it is the electrical Birkeland currents that flow from the sun to the Earth that drive the light show. As these electromagneticed fields change shapes, so do the aurora.

Jupiter and even Mars also experience similar events which are also driven by Birkeland currents.