Of course without the Sun the Earth would be dark, but beyond the darkness the Sun is intricately involved with everything that happens here. Perhaps the most important event which we take for granted namely; photosynthesis would be impossible without the Sun. By that process the Sun's light, water, and air cause plants to make the food they need to grow. Without sunlight there would be no green plants. However, not only would plants disappear but the animals like cows, sheep, insects or fish that depend on green plants for food would also disappear. All animals either eat plants or animals that eat plants. Without sunlight all forms of life would cease to be. Since our food chain rises from plants to animals to human beings, without the process of photosynthesis there could be no life on this planet.
Even if there were another food source our lives would be more difficult without what we term natural resources. Imagine a life without automobiles, airplanes, or the possibility of heating or cooling our homes. We get energy from the Sun. From before the age of dinosaurs there was vegetation that died and then was buried underground or under the oceans. As time went on this vegetation was turned into what are termed fossil fuels like gas, oil, or coal. What we term Earth's natural resources would not exist without the sun. Those natural resources needed the sunlight to form. Even now we are still trying to harness the power of the Sun to heat our homes, power automobiles by developing solar collectors and solar cells.
Light from the Sun provides us with illumination. Without the Sun we could not see. Light from the Sun travels at 186,282, miles per second (299,792 kms per second). Even at this fast speed it takes about eight minutes for light to reach the Earth. Light is any source of illumination. It can be found in nature like the Sun or man made light like the light bulb.(17)
All light travels as waves. The distance between the crest (top) of the waves is the wave length. As the wave lengths get wider the frequency becomes lower, and conversely the shorter the wave lengths the higher the frequency. For us the most important part of the light spectrum is natural sunlight which is called white light or visible light. This is the light we can see. However, if light is put through a prism the white light breaks up into 7 colors of visible light: red, orange, yellow, green, blue, indigo, and violet, as well as infra-red and ultra-violet that we cannot see.
Every element gives off a different set of spectral lines. This is how scientists study the sun and other objects out in space despite them being so far away. The stars are classified by the color they appear to us on earth. As the temperature of the star increases the bluer the star appears to be.