Our Sun is a star, and together with all the stars that we can see at night, it is part of an enormous assembly of stars called The Milky Way Galaxy. The word galaxy is the name used for very large numbers of stars that are part of the same related group. The Milky Way Galaxy is just one of many existing galaxies.
Compared to the Earth, the Sun is very large and very far away. It is a million times larger than the Earth and is 300,000 times heavier. Rotating on its axis, which is slightly tilted, the Earth travels an immense distance through space on an elliptical orbit around the Sun, taking one year, actually a little more than 365 days, to complete one orbit, moving at a speed of about 67,000 miles per hour at an average distance from the Sun of about 93 million miles. It is the combination of the orbital motion of the Earth and the tilt of its axis of rotation that results in the Earth’s seasons.
There is land and sea, solid rock and water, on Earth, a world surrounded by an atmosphere of air, but on the Sun there are no rocks or water, no solids of any kind. The Sun is a huge ball of very hot gases, about 72% hydrogen and 27 % helium, and the remaining 1% is made up of many of the same materials that exist on earth, called elements, but on the Sun in a gaseous state. The visible outer layer of the Sun, called the photosphere, is composed mainly of hydrogen at a temperature of about 5,500 degrees Celsius. Deep in the interior at the core, which we cannot see, the temperature is calculated to be fifteen million degrees Celsius or more and the pressure there is 300 billion times that of the atmosphere at the surface of the Earth with a density of about 12 times that of solid lead on Earth. It is this extreme heat and pressure at the core that enables and maintains the nuclear fusion processes that generate the Sun’s heat and light. In simple terms, it does so by converting hydrogen to helium in a very complex multi-step fusion process that also releases immense amounts of energy that slowly makes its way from the core to the surface and streams out of the sun in all directions in the form of heat and light and other radiation. Just a small portion of that total output reaches earth while the rest streams out into space. This radiation is called the Solar Wind.
In the continuous fusion process, about four million tons of the Sun’s mass is converted into energy every second. Even at this prodigious rate, the Sun should continue to exist for another four and a half billion years or so, although by the end of that far distant time it will change in size and composition and the amounts of energy emitted.
Sometimes in the evening at sunset if there is a somewhat hazy atmosphere, we may see the sun as a distinct solid red circle outlined against the sky as it begins to disappear below the horizon. We speak of the setting sun but in reality the sun stays in a fixed position in relation to the Earth and it is the earth that is turning, rotating slowly, that gives the illusion of a setting sun. But, a word of caution is required here. Unless it is screened by the atmosphere at the horizon in this way, where the Sun’s rays are not shining through, NEVER look directly at the sun, it is dangerous to do so because its brightness can cause damage to the eyes, even perhaps, to the extent of blindness. Also, for an additional caution, the light emitted by the Sun includes ultra violet rays that are harmful if the skin is exposed to them for too long a period of time, causing not just painful sunburn but also, with repeated exposures, damage to the skin that can lead to a possibility of a not uncommon form of skin cancer.
The Sun is at the center of a system of eight planets, together with their satellite moons, and many smaller bodies called asteroids, meteoroids, and comets, all orbiting the Sun at different distances and rates of speed. Collectively, these comprise The Solar System and occupy a disc shaped region of space within the Milky Way Galaxy. The Sun, accounts for about 99% of the mass of the entire system.
The Sun is the ultimate source of all energy and sustains life on planet Earth.
