In our Solar System, the Sun lies at the center and everything goes around it, a fact first realized by the ancient Greek mathematician and astronomer Aristarchus of Samos in the third century BC.
The star we call the Sun is a gigantic ball of burning gas, with a diameter of 840,000 miles. It is so big that over a million Earths could fit into it. The surface of the Sun, the Photosphere, has a temperature of 5,500 degrees celsius. At the core of the Sun, temperatures reach a massive 15.6 million degrees celsius. Inside the Sun, hydrogen atoms are fused together into helium, releasing energy (heat)in the process. The Sun consumes 4 million tons of hydrogen every second and its energy output is a whopping 386 billion billion megawatts
To put it another way, in 15 minutes the Sun produces as much energy as the whole of Humankind uses in a year. It can maintain this output for another 5 billion years or so.
The Sun spins on its axis, just as the planets do, but being gaseous the speed of rotation varies with latitude. This warps the Sun’s magnetic field and causes magnetic eruptions, which show up as dark patches known as sunspots, on the surface. These are cooler, only 4000 degrees C. Eventually, the Sun’s magnetic field collapses and the north and south magnetic poles swap position. Then the whole process starts again, completing a cycle every 22 years. Sunspots are at their maximum during the period when the poles are swapping. These fluctuations in the magnetic field are associated with solar flares, huge jets of solar gas flung far out into space. They can be accompanied by dense clouds of electrically charged particles known as the ‘Solar Wind’, flung out at a speed of 450 KM per second Occasionally, intense bursts of this disrupt communications on Earth.
Life on Earth totally depends on the energy emitted by the Sun. Sunlight makes possible photosynthesis and plant life supports both herbivores and their predators, the carnivores. The Sun drives our atmosphere and weather systems. It also affects us in more subtle ways. The Sun’s UV radiation on our skin is our principal source of vitamin D. This is important for healthy bones, muscles and the proper functioning of our immune systems. As we all know though, too much exposure to UV carries the risk of skin cancer and cataracts. The Sun also stimulates the Pineal gland in the brain. This gland produces chemicals called Tryptamines which improve our mood. Sunshine really does make us feel good!
We know that at some point in about 5 billion years’ time the Sun will change though. As it continues to consume its hydrogen and release energy, it will reach a point when the balance between the gravity pulling it in and the energy pushing it out will be destabilized. The center will contract and become hotter, but the outer regions will expand and become cooler. At this point, life on Earth as we know it will become impossible. Ultimately, energy production by the Sun will end and the whole thing will collapse.