The sun

The Sun is the most prominent and important feature of our solar system. It is the largest object in the solar system, constituting approximately 98% of its total mass. The Sun today consists of about 74% hydrogen, which amounts to 92% of its volume. There is also helium, which accounts for 24% mass, and 7% volume. Finally, there are traces of other heavier elements like silicon, sulfur, neon, calcium, chromium, magnesium, carbon, iron, nickel, and oxygen. The Sun is classified as a yellow dwarf star, and as such has a relatively insignificant role in the Milky Way it resides in. It does however take a central role in our solar system, where it holds all planets, asteroids and comets in a strong gravitational grip.

The visible outer layer of the Sun is known as the photosphere, and its temperature is roughly 6,000 degrees Celsius. Inside the Sun’s core, solar energy is created. The temperature and pressure within this region are so high that nuclear fusion takes place. In this process, four hydrogen nuclei fuse together, forming one alpha particle, or helium nucleus. Due to convective processes, the energy which is generated in the Sun’s core takes about a million years to reach the surface, only to be beamed to Earth in only 8 minutes. The distance between the Sun and the earth is roughly 150 million kilometres (1 Astronomical Unit, AU).

The Sun is actually a star that is magnetically active. A strong, dynamic magnetic field is supported by it, which changes from year to year. It also changes in polarity every eleven years, an event which signifies the beginning of a new solar cycle. Though we have learnt a lot about the Sun over the years through constant research, many questions remain a mystery – like the origins of flares, the regular cycle of sunspot activity, etc. Since electromagnetic storms can be a danger to astronauts, satellites and the power grid, it is important to learn more about the occurence and predictability of solar phenomena.

Sunlight is our primary source of energy. The light and heat from the Sun support the oxygen-forming process of photosynthesis and are also responsible for our climate and weather. On Earth, we all need and rely on the sun. Plants capture the incoming solar radiation and convert it to oxygen and reduced carbon compounds. Animals (and humans) need the sunlight not only for the heat, but also for both vision and necessary vitamin supplies. More recently, humans have learned to make use of the sunlight in another way: by constructing solar cells, we are able to convert sunlight into a direct electric current. The amount of incoming solar radiation per unit area deposited by the Sun is called the solar constant. It should be noted that the solar constant, although called a constant, varies with Earth’s distance to the sun. Naturally, the actual amount of sunlight we receive is strongly dependent on many factors like latitude (your position on Earth), the time of day, the time of year and local weather conditions.

The Sun has been active for a staggering 4.6 million billion years, and is expected to go on for another 5 billion years. Once the solar core is depleted in hydrogen, the loss of radiation pressure causes core collapse. Since this further elevates pressure and temperature, the sun will start fusing helium into heavier elements. During this process the star will swell so large, that it might swallow the Earth. It will then collapse into a white dwarf, and take a trillion years to cool down.

The birth of our sun (video)

The death of our sun (video)