The chromosphere begins at the upper limit of the photosphere. It is the layer, which becomes visible in the first phase of a solar_eclipse. It is also called the middle atmosphere.
Unlike the photosphere, which is only 400 kilometers thick, the chromosphere is up to 10,000 kilometers thick. Temperatures are several tens of thousands of degrees Celsius. Gas density drops here.
The chromosphere is not actually a uniform layer, but rather a system of complex structures. Here, countless gas jets called spicules shoot upwards at great speeds. An average spicule has a diameter of about 1000 kilometers and shoots upwards at a speed of 30 kilometers per second. After a few minutes, the gas jets fall back again. They are probably associated with a strong magnetic_field.
Using special filters, spicules can be observed not only at the edge of the Sun, but over its entire surface. Chromospheric flares, which lie far above the photospheric ones, can also be observed. These can be as much as 100,000 kilometers long and 10,000 kilometers in diameter.
