Sun Facts: Do You Know What a Solar Corona Is?

The Sun has always deserved human attention. Worshipped by ancient civilizations, the star has been seen with curiosity and holds secrets that scientists are still looking to unveil.

Have you ever seen a solar eclipse? If you have heard about the phenomenon, then you probably know that it occurs when the moon partially or totally covers the sun (from Earth’s view), preventing a large amount of light to reach Earth.

Try to remember the last eclipse that you witnessed. While experiencing this unique phenomenon, you probably noticed that there was an intense aura surrounding the sun. But, where does that light came from?

In this article we will explore one of the Sun’s mysteries and present you the Solar Corona: the hot burning plasma that surrounds the sun and other celestial bodies.

Solar corona facts

The word Corona is Latin for “crown” and is used to describe the layer with a temperature of 1 to 3 million Kelvin degrees. In fact, the Sun’s atmosphere has three main layers. Separating the surface of the Sun (photosphere) from the corona is the chromosphere.

The solar corona has an extension of several million miles outward from the other two spheres. A curious fact is that Corona temperature’s largely surpasses the temperatures of both photoshphere, which registers an average temperature of 5800 Kelvin, and chromospheres, which goes to about 25,000 Kelvin.

Although there are many theories, the reason for Corona’s such high temperatures has not been totally discovered. Some scientists think that it could be explained by the Sun’s natural magnetism and rotation.

Solar corona is composed of the same elements that are in the interior regions of the Sun, with hydrogen being the one the most abundant. Corona’s behavior resembles that of gas – it is simultaneously hot and bright. However it cannot be considered as a gas because it is composed of charged particles – protons and electrons that move at different velocities.

The temperature is not always constant and the Corona is unevenly distributed across the Sun’s surface. Scientists use the expression “Quiet Sun” to describe solar regions that, during a certain period of time, are not registering any activity or experiencing a phenomenon called “coronal hole ”.

Solar corona “magnetic braids”

Most of the Sun’s phenomena occur in the active regions due to the influence of its magnetic field. Active regions are activity zones parallel to the solar equator. Different sun events (like sunspots, facula or flares) occur in the 3 layers that surround the star.

In 2013, The High Resolution Coronal Imager (Hi-C) telescope revealed “magnetic braids” around the sun’s outer atmosphere. Scientist think that these braids might be the answer to the extremely high temperatures of the Sun’s Corona.


According to Jonathan Cirtain, head of the Hi-C project, they observed “a bundle of magnetic fields, wrapped about several other bundles to form a magnetic bundle ensemble”. Like a braid, “the magnetic fields in this ensemble have varying lengths, and the rate of curvature along individual field lines may also vary such that some fields are very highly curved while others are less so”.

When a high curvature occurs, the magnetic braid becomes unstable and is forced to interact with the opposite one. During this phenomenon, an enormous amount of energy is released which is possibly responsible for the heat of the plasma, the acceleration of flares and other massive outbursts.

What is a coronal hole?

Coronal holes are areas of the sun’s corona where the temperature is not that high. During this phenomenon, polar regions of the Sun become darker and release considerably less radiation. Simultaneously, the Corona becomes thinner producing conditions ideal for the release of solar winds.

Solar winds are just a large stream of plasma that travel in the upper atmosphere of the sun. The stream consists of an immense discharge of protons and electrons, released at supersonic velocity. The protons and electrons that escape the solar wind result in the enchanting Aurora Borealis that we see on the Earth’s northern and southern poles.

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Gayrajan Kohli
Gayrajan Kohli
Gayrajan is a staunch solar promoter, serial entrepreneur & management consultant. He has a decade of experience in solar PV, disruptive technologies and political consultancy in USA and India. He believes that development of solar and other renewable technologies is critical to India's energy security. Gayrajan holds a Masters and a Bachelors in Electrical Engineering from USA. Follow him on Twitter to gain daily industry insights.
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