Like all other stars, the Sun is a huge ball of extremely hot and largely ionized gas. Over the years, we have learned many things about the Sun and its atmosphere. Let’s see what we exactly know about Sun’s atmosphere.
Sun does not have a plain or solid surface, instead has a very heated atmosphere that is made of solar material and is bound by gravity and magnetic forces. There are several layers in Sun’s atmosphere mainly the Photosphere, Chromosphere, and Corona.
The photosphere is the lowest layer of the Sun, the lowest layer that we can observe directly. It ranges from 11,00 degrees Fahrenheit at the bottom to 7460 F at the top. The photosphere is about 500 kilometers thick. It consists of bright bubbling granules of plasma and darker, cooler sunspots. The photosphere also consists of solar flares. Solar flares are the explosions that take place due to high magnetic fields.
The chromosphere is a very thin layer, that emits a reddish glow. This glow generally can only be seen during a total solar eclipse. At other times, it is very weak to be seen against the bright photosphere. The plasma present in the chromosphere has a very low density as compared to the photosphere. Chromosphere plays a role in conducting heat from the inner layers of the Sun to Corona its outmost layer.
Corona is the third and the outermost layer of the Sun. Just like Chromosphere, Corona can also be seen only during a total solar eclipse. It appears like white flames of gases flowing outwards in space. The temperature here can get up to 3.5 million degrees F. When the gasses cool down, they become solar wind.
In August 2018, NASA launched Parker Solar Probe to explore the Sun and its atmosphere by traveling closer to it than any other spacecraft ever has. And after 3 years on 28th April 2021, it passed Alfven critical surface. Alfven critical surface is a point at which the gravity and magnetic field of the Sun are too weak to contain solar material. This Alfven critical surface marks the end of the Sun’s atmosphere and the start of the solar wind. Until now, researchers were not sure about the exact location of the Alfven critical. But Parker told scientists that it has crossed Alfven critical when it encountered the specific magnetic and particle condition on 28th April 2021. It was at 18.8 solar radii above the solar surface at the time.
Alfven critical surface is not shaped like a smooth ball. Parker solar probe, during its flyby, passed several times in and out of corona which proved that Alfven critical has spikes and valleys that wrinkle its surface.
Psuedostremer is like an Eye of a storm. Psuedostremer is a huge structure that rises above the Sun’s surface. It can be seen from Earth at the time of the Solar Eclipse. Psuedostreamer is situated in Corona, the third layer of the Sun’s atmosphere. In a Psuedostremer, the condition is quiet, particles are slow and the number of switchbacks is dropped. It is a significant change in conditions found in the solar wind.
There is a zig-zag-shaped structure in the solar winds. This structure is known as Switchbacks. When NASA-European space Agency flew over the poles of the Sun in the 1990s, they discovered some zig-zag paths. For years, scientists thought that these zig-zag paths(switchbacks) are oddities confined to Sun’s polar region.
In 2019, it was discovered, switchbacks were rather common in the solar wind. Scientists found the switchbacks originated in the Photosphere where there is a high percentage of helium.
As more solar missions and research happens, we will know more about our star Sun and its atmosphere. It will help us understand the Earth-Sun system and life around it well.