CHROMOSPHERE
Is the next-to-last solar layer and is characterized by its reddish color visible during a total solar eclipse or using a solar telescope specially designed for this kind of observations (a telescope with an alpha -Hα hydrogen filter). On this layer, way less dense than the previous ones, it can be observed phenomena such as spicules, which are plasma jets moving at 20 km/s from the photosphere to outer space. Spicules can happen anywhere in the solar sphere, and last around 15 minutes.
Unlike the rest of the Sun, it is observed that on this layer, as it moves away from the center, the temperature increases from 4,200 °C in the outer part of the photosphere to about 25,000 °C, 2,000 km in the “upper” part.
A definitive explanation of what causes a temperature inversion is still under discussion, although the local magnetic field is likely to undergo some variations, known as magnetic reconnection. That is how the energy of the magnetic field turns into motion and heat, which increases the temperature on this layer.
CORONA
The corona is the outermost layer of the Sun. It extends a few million kilometers into outer space but is not that dense, just like a billion times less than the photosphere. On the other hand, its temperature is way hotter, hitting temperatures between 1 million and 3 million Celsius. This layer is visible during a solar eclipse or using coronagraphs designed to observe it. It is worth mentioning that it is probably one of the most breathtaking and iconic views of a total solar eclipse. The corona does not have a well-defined, symmetrical shape, and it depends on the solar magnetic cycle.
What is the solar magnetic cycle?
The Sun, like the Earth, has two magnetic poles: the north pole and the south pole. Every eleven years, these poles turn upside-down, and the one in the north moves to the south, which is known as the magnetic cycle. This situation generates changes in the emitted Sun’s radiation (less than 0,1 %) as well as in the plasma amount ejected from its surface. During the maximum magnetic activity of the Sun, most sunspots, solar flares, and others are observed in the photosphere.
Studying these changes is essential since they cause effects on space and Earth, mainly on an atmospheric level, producing auroras and, in the case of stronger events, they can even affect satellites orbiting around our planet.
