How does aurora form? | What are solar storms and how it affect us ? | CME

The aurora borealis also known as Northern lights near "North pole" and aurora australis near "south pole". 

There are mainly two reasons why this happens:- 

1. Solar wind 

2. Earth's magnetic field 

Let's understand the first one "Solar winds"

The sun sends us a lot of other energy and small particles our way. Let's see how? The sun is made up of billions of particles probably 91% of hydrogen and 8.9% of helium and 1% of other gases. Sun can be divided into 6 layer or regions.

1. Corona 

2. Chromosphere 

3. Photosphere

4. Convection Zone

5. Radiative Zone 

6. Core

Credit:- NASA

1. Corona:- This layer consist of plasma and it is the outermost layer of the sun's atmosphere. It is above the chromosphere and is easily visible during total solar eclipse having a temperature of 500,000 Kelvin.

The Sun's corona and is visible to the naked eye.
Credit:- https://lucnix.be/, Luc Viatour  

2. Chromosphere:- The chromosphere is visible as a coloured flash at the beginning and end of solar eclipse. Chromosphere extends up to 2000 km into the corona. It has a red colour due to electromagnetic emissions. It is also observed on stars other than sun. The temperature here is 4000 k to 8000 k approximately.

3. Photosphere:- the outer shell of the star from which light is radiated. The deepest layer which we can observe directly. The temperature here where is from 6500 k to 4000 k.

4. Convection zone:- this layer is unstable due to conviction. It consists of mass movement of plasma which usually comes from circular convection current. What is circular convection current? It is, when water gets hot it rises and when it cools it sinks. This makes the magma rise (like boiling water). Then when it reaches the top the magma cools from the crust it sinks back down to the core. Just like the water, the magma creates movement of a circular motion called convection currents.

5. Radioactive zone:- here the radiation is so dance that before photons travel a very short distance they are absorbed or scattered. It takes 171,000 years for gamma rays to leave the radioactive zone.

6. Core:- the hottest part of the Sun. It has a density of 150 g/cm³ and a temperature of 15 million k approximately. It is made of hot dance plasma and has pressure to be estimated of 3.8 PSI.

Now we know about its layers, let's see what are solar winds? Well, they are the charged particles that consist of electrons, protons and alpha particles with kinetic energy of 0.5 to 10 kev. This particles are released from corona. Solar winds very in temperature, speed and density. They can escape the sun's gravitational pull because of their high energy and high speed. It's speed is 1 million miles/hours. One more thing,

The velocity component perpendicular to the magnetic field creates circular motion, whereas the component of the velocity parallel to the field moves the particle along a straight line.

Credit:- https://openpress.usask.ca.

coronal mass ejection

The black spots you see in the above picture are the areas where temperature is gradually low compared to other areas.
Credit:- NASA

Coronal mass ejections causes highly energetic eruptions from the Sun, providing the main source of major space weather events. Millions and billions of terms of plasma from the sense atmosphere gets ejected and speeding it up to 9 million km/h. The gas clouds produced by CME be sometimes larger by sun itself. Around 2 days later they will reach Earth. This is known as solar wind. If this solar winds hits our planet then it would cause an extinction . Solar flares are ejected regularly from the sun's surface. Do solar wind hits earth? Well solar winds hits earth but we are protected by the Earth's magnetic field and its atmosphere. 

What would happen if a solar flare hits earth?

In the year 1859, Carrington noticed that there are  high flares on sun, he saw that for at least 5 minutes and noted what he observed. After 17 hours, something dangerous happened earth was strked by geomagnetic storm! When this happened Arora was seen all over the earth. It was so bright that minors in USA woke up to make breakfast for themselves. Report says that people were able to read newspapers. There was not much of technology at that time but telegraphs were invented. 

The telegraph and electrical grids where overwhelmed by the electricity pushed through their wires. Operated squad electrical shocks from the telegraph machines and the telegraph paper were lit on fire. Even though, if telegraph was not connected to the circuit but still telegraph were able to communicate each other.

Telegraph operator tries to adjust the equipments they received shocks in return even if it was not connected to the circuit. This event is known as Carrington event.

How it happened?

According to Faraday's law, when flux changes through the coil then there is an induced EMF and induced EMF generates current.

That's it!  

What would happen if any solar storm hits us today ?

If any solar storm hits us today then world could face loss of 10¹¹ US dollars also it may result in fires. It would destroy our navigation systems and underwater internet cables. But NASA does keep a close eye on our Sun with satellites such as SOHO in case it decides to flare up in our direction, and ongoing missions headed towards the Sun such as the Parker Solar Probe will collect enough data on our host star to help scientists predict its behavior.

Credit:- NASA, NOAA

Color of aurora

The color of an aurora depends on the intensity of charged particles. If you see red aurora, then charged particles have low energy. The oxygen atoms give low-frequency red light. You can see a green aurora when more energetic particles slam into oxygen. The high energy of particles causes the oxygen atoms to release higher-frequency green light. If energy is even more higher than particles cause nitrogen atoms to glow blue. If the nitrogen atoms begin to decay, they emit a purple coloured light. This is a rare colour to see, and usually only happens during a particular time.