Sun

NASA uses the unique vantage point of space to understand and explore our home planet and our home star in order to achieve our vision: To improve life here, extend life to there, and find life beyond.

The relationship between the Sun and the Earth is at the heart of a complex, dynamic system we do not yet fully understand. The Earth-Sun system, like the human body, is comprised of diverse components that interact in complex ways, requiring unique capabilities for characterizing, understanding and predicting change. Therefore, we need to understand the Sun, the heliosphere, and Earth's atmosphere, lithosphere, hydrosphere, cryosphere, and biosphere as a single connected system.

At the center of our solar system is the Sun, a magnetically variable star. This variability has impacts on life and technology that are felt here on Earth and throughout the solar system. NASA is working to understand the Sun, our own star, and the Earth, our own planetary system, because they comprise the only star-planet system we can investigate in detail. Using our view from space to study the Earth-Sun system, we can also better predict critical changes to Earth and its space environment.

INTRO:

One of the most important features of every day life is the sun. It rises and sets, and we use it to fix our daily routine. Without it we would not receive the light and heat that provides us with energy. This star, our sun, is very unique. Most stars are visible only at night, but our sun is visible at daytime. It is the closest star to earth. Since the star is so close to us, we are able to know much about its surface. Similar to all stars, the sun is a ball of hot gas. It has an interior as well as an atmosphere. The sun's surface is known as the photosphere. It's surface is largely uniform in brightness and becomes slightly darker on its edges. The sun is one of our sources of energy. Nuclear fusion is the process by which energy in the sun is formed. Groups of four hydrogen atoms are changed in to a single helium atom.

THE SUN AND US:

The sun is a star located at the center of our solar system. Although we can see many stars at night, the sun is the only one that we can see during the day. The sun is the biggest object in the solar system, as well as the most important. It's gravity keeps the planets from spinning off in to space.

The sun is also important for our life on Earth. It provides us with food, wind, weather, and tides. It contributes power for our factories by running windmills and hydropower. The sun also provides us with electricity that is generated by fossil fuels, such as coal, gas, and oil. These fuels are nothing more than stored sunlight. Solar energy does not pollute, is almost free, and will not run out for some five billion years.

Our bodies are provided with energy from the sun as well. It triggers photosynthesis to occur in green plants. The process traps the sun's energy and turns it in to carbohydrates. By eating these plants, animals convert this energy in to a type they can use. These carbohydrates are passed up the food chain.

The sun plays an important role in our weather. The sun's rays hit the ground and the warm ground heats the air above. Warm air from the equator moves north and south to the poles, making winds. The sun warms the oceans, and makes water vapor. The vapor rises and forms clouds. When the droplets are large enough, they fall back down to the earth as rain, sleet, snow or hail.

LAYERS OF THE SUN:

Close up, our sun is not as amiable. Its outer layers are extremely hot, bubbling, and full with explosions. The first layer, the photosphere, looks like the sun's surface. In the photosphere, hot gases rise and cool. These are known as convective cells. Upon reaching the surface, they look like small freckles, known as granules. The temperature of the photosphere is about 10,000 degrees Fahrenheit, which is much cooler than what is above and below. But it is the photosphere that sends heat and light in to space. These waves travel at 186,300 miles per second, and reach Earth within approximately eight minutes.

The next layer is the chromosphere. The best time to see this layer is during a total eclipse, which is when the moon blocks the sun's disk. The chromosphere appears as a thin, pink ring around the edge of the sun. The bottom part of the sun's atmosphere is irregular in terms of its shape. Its depth can vary from 1,000 to 10,000 miles. Giant flames, or spicules, make the chromosphere irregular. Spicules are made of hot gases that shoot from the chromosphere in to less dense area. They can extend up to 10,000 miles and travel at 17 miles per second.

The corona is also best studied during a total eclipse. It appears as a pearl white layer extending out around the sun. The corona is the top layer of the sun's atmosphere. It is made up of very hot, thin gases and stretches more than 1 million miles from the photosphere. Its one million degrees hotter than the sun's surface due to violent explosions from below, such as sunspots, prominences, or solar flares. With these high temperatures, the corona is constantly expanding and changing shape.

2. How We Depend on the Sun

The Sun gives us heat, light, our food, and the air that we breathe. It powers the atmosphere to give us the winds and rain. Even the coal and oil that generate electricity for light and power come from plants and animals that lived hundreds of millions of years ago and depended on the Sun for life.

The Sun heats the land, oceans, and air. It evaporates water from lakes and oceans. When the water vapor cools, it drops as rain or snow, giving us the moisture we need for drinking water and for plants and animals to grow.

Green plants use the Sun's rays to turn carbon dioxide and water into carbohydrates. At the same time, they release oxygen that we use to breathe. This process of production of carbohydrates by green plants is called photosynthesis. The carbohydrates formed by the plants are used by them to grow, and we use plants for our nourishment.

Without the Sun, the Earth would be a dark, cold, dead place.