It is the outer atmosphere of sun. Where the temperature is very high. Even more high temperature than sun’s photophere(actual surface). Scientists believe high temprature in outer atmosphere because of solar flares. But further research is going on by various missions of agencies. NASA’s Parker mission is a first mission named on a actual person. Parker mission objectives are to study the corora by phycally going closer to surface. Means Parker probe will go closer to sun and will be first probe to go that much to sun. India’s Aditya mission also about inspection of sun which will be launched after 2022.
Corona’s outermost layer can get more than 1,000,000 degree celcius. Corona is outer just environment of sun which have more temperature than even photosphere which is actual surface. Is not it wierd? Yes it may be, thats why space agencies are funding so much money to research these phenomena.
It is actual surface of sun. From where solar flares or heat energy in simple words released. Here temperature is about 6000 degree celcius. This is where sunspots we see. Gas jets shoot out from here. This is the area which is visible during solar eclipse. India’s space agency ISRO is about to conduct inspection on all three corona, photosphere, chromosphere.
Above image we see in telescope is the photosphere. Red liquid that are emitting these are actually gas jets shootout.
Its is just above the photosphere below the corona. Layer of approximately 2500km wide between corona and photosphere. When we move from inner circle that is red to outer circle, its color turns to pink. This 2500km thick layer visible only during solar eclipse. That much information is enough for exam point of view. But further you can extend your knowledge from here.
On photosphere we can see black spots. These are called sunspots. They have a cycle of 11 years. These are the areas having high magnetic field that is why they appear black. We know that sun’s magnetic field affects out communication systems on earth. That is why missions on sun are necessary.