The Sun the star of the neighborhood from its formation to its inevitable end
It is the largest body near us giving us and all the planets light heat and gravity allowing life and also putting it in constant danger. A journey through the solar system the first article in the series
Among the stars shining in the night sky of Earth there are seven planets one Sun and additional planetary bodies that make up our neighborhood in the wide universe the solar system. Their relative closeness to us allows us to study them and maybe also dream of visiting them and even establishing colonies on them one day. This series of articles is dedicated to our neighbors in the solar system. Who are they and what do we know about them
Countries rise and fall leaders come and go again and again humanity discovers new findings records are broken and natural disasters strike. Against all these constant changes one thing we know for sure the Sun will shine tomorrow.
The Sun is the only star in our small neighborhood which is named after it the solar system. Moreover it is also the largest and most significant body in the system. How large Almost 99.8 percent of the mass in the space near us is concentrated in the Sun itself.
In the beginning there was a nebula
The Sun was formed about 4.5 billion years ago from a huge cloud of gas and dust called the solar nebula. The nebula gradually collapsed under its own gravity its rotation sped up similar to what happens when an ice skater pulls their arms closer to the body to spin faster and it flattened into a disk.
Because of the spinning motion more and more material accumulated at the center of the mass and its speed perpendicular to the axis of rotation increased thanks to the conservation of angular momentum. The cloud spread outward and in its center a round and very dense clump formed the core from which the Sun later developed. The rest of the cloud less than one percent of all its material continued spreading outward rotating around the forming star. This flat disk is the ecliptic plane the plane in which the planets orbit the Sun.
For about one hundred million years the spherical clump at the center grew and its material mostly hydrogen and helium compressed further. It gradually became so large and dense that the temperature soared to millions of degrees Celsius.
At this stage some of the small clumps of matter remaining near the new Sun were swallowed by it as well. The more distant clumps that the Sun’s gravity could not pull inward began to accumulate at the edges of the disk and to orbit around it. From these few stable clumps the planets of the solar system were formed.
Although the Sun is the center of our solar system and all the planets orbit around it it does not stand still. The Sun and its planets move in an orbit around the center of our galaxy the Milky Way. It completes this orbit at a dizzying speed of almost 800 thousand kilometers per hour.
Layered mysteries
The Sun is made of several layers like an onion. Their composition is similar plasma of hydrogen and helium but their temperatures differ greatly. The temperature on the surface of the Sun reaches about 5500 degrees Celsius but this burning heat is nothing compared to what happens deeper inside the core of the Sun. There the temperature can reach about 15 million degrees.
The innermost layer is the core the hottest and most dense place in the solar system and its radius is about one quarter of the entire radius of the Sun. Inside the core there is immense pressure created by the huge mass of the outer layers. The combination of enormous pressure and extreme temperature creates nuclear fusion in which hydrogen nuclei fuse into helium. This process releases a great amount of energy in the form of light and heat which the Sun emits and which allows life on Earth.
Around the core are the radiation and convection layers where the temperature drops from about seven million degrees to two million degrees as you move outward. The radiation layer acts as an insulating layer that keeps the heat inside the core. Above it is the convection layer where enormous bubbles of hot plasma rise toward the photosphere the layer we see as the Sun’s visible surface.
The energy from the core takes about 170 thousand years to pass through the convection zone. The outermost layers are those we can see and consider the Sun’s atmosphere. The photosphere is a thin envelope on which the famous sunspots appear magnetic whirlpools that look like dark spots. Above it is the chromosphere a thin red orange layer visible mainly during total solar eclipses.
The outermost layer is the corona. In the corona huge explosions occur due to magnetic activity. Surprisingly this is the hottest layer reaching about three million degrees Celsius even though it is the farthest from the core. The reason for this temperature jump remains a mystery. It can be seen clearly during total solar eclipses as a glowing halo.
Another mystery is the Sun’s magnetic cycle. Every 11 Earth years the magnetic poles flip. At the peak of the cycle there is increased magnetic activity with more solar flares and more ejections from the corona. Material leaving the corona at supersonic speed is called the solar wind and this flow of charged particles creates a giant magnetic bubble around the Sun called the heliosphere. The heliosphere extends beyond the orbits of the planets. Earth like all the planets is located inside the Sun’s atmosphere.
Because of the layered structure the rotation time of the Sun varies meaning the poles rotate slower than the equator.
There is something new under the Sun
The Sun is one of the most fascinating celestial bodies we study and compared to many others it is relatively close to us. But this closeness also has consequences because processes on the Sun can affect us. That is why studying the Sun is important not only for curiosity but also for protection.
NASA has launched many spacecraft to study the Sun. The probe that reached closest is the Parker Solar Probe launched in 2018 the first spacecraft to enter the corona. In December 2024 it made history by reaching a distance of 6.2 million kilometers from the surface. During this passage it broke the speed record of any human made object reaching about 690 thousand kilometers per hour.
The mission which cost about 1.5 billion dollars was meant to help scientists understand the mechanisms behind solar eruptions and the extreme temperatures of the corona. Earth’s magnetic field blocks most charged particles from the Sun but sometimes the Sun releases a billion tons of such particles at once which can damage satellites navigation systems and in extreme cases even electrical infrastructure. To prevent damage and develop warning systems the Parker probe was sent to study the inner processes that collect and accelerate the particles. It is protected by heat shields that withstand solar radiation of up to 650 kilowatts per square meter and temperatures of about 1370 degrees Celsius.
There are several other major missions. In 2006 the Stereo project launched two identical probes one ahead of Earth and one behind it in orbit around the Sun providing a three dimensional view of solar eruptions. Another spacecraft is SDO launched in 2010 which studies the magnetic field of the Sun and solar activity.
Another mission is Solar Orbiter a cooperation between NASA and the European Space Agency launched in 2020 to study the poles of the Sun which may play a key role in solar eruptions. It complements Parker from a different angle.
Seeing the light
It is easy to spot the Sun in the sky but observing it is another story. It is dangerous to look directly at the Sun even with sunglasses. To observe its storms and sunspots you need a special solar telescope.
Although we expect to see the Sun during the day it is responsible for one of the most beautiful night displays on Earth the aurora. It appears as colorful patches of light usually green but sometimes red yellow blue or purple over the polar skies. The aurora forms when charged particles from the Sun are guided by Earth’s magnetic field toward the poles where they collide with atmospheric gases causing the glowing colors. During strong solar storms the aurora can appear farther from the poles.
A stunning display of colorful lights occurs when the particles of the solar wind meet Earth’s atmosphere.
The future of the Sun
The Sun is a middle aged star formed around 4.5 billion years ago. It is stable now continuing to fuse hydrogen into helium. But nothing lasts forever. As fusion continues the helium concentration in the core rises. In about five billion years the Sun will finish most of its hydrogen supply and will contain mostly hot compressed helium.
At that stage the Sun will lose stability and begin dramatic changes. It will expand and swallow Mercury and Venus. Even if it does not reach Earth’s orbit Earth will likely be pulled inward. The Sun will emit much more energy causing all Earth’s oceans to boil and no known life form will survive.
As it expands gravity on the outer layers weakens and much of the material will be blown into space. The remaining helium will fuse into carbon and oxygen releasing large amounts of energy. Eventually the Sun will become a red giant then shed its external layers leaving behind a white dwarf the dense core no longer producing energy. Its size will be similar to Earth but extremely dense and mostly carbon.