The Sun is composed of three layers. The layer we can see with the naked eye here on Earth is the photosphere which is the only visible layer of the Sun. Beyond that is the chromosphere, which is hotter than the photosphere. The corona is the hottest and outermost layer of the atmosphere. It consists of low-density gas with a temperature greater than one million degrees Kelvin (1 million Kelvin is equal to 999,727 degrees Celsius). To prevent permanent damage to the eye, humans should only view the corona with the naked eye during a solar eclipse.

An image of the layers of the Sun. click for copyright

Unlike here on Earth, the Sun does not require oxygen to be "on fire," as we would like to describe it. In fact, the Sun is a large nuclear fusion reaction that takes place at its center. The reaction is actually the fusion of hydrogen into helium, which takes place at the center of the Sun. As the energy travels through the layers of the Sun over millions of years, the temperature of the energy decreases as it moves farther away from the fusion reactor. Once reaching the surface, this energy circles the Sun in the form of convection currents. It then leaves the Sun and heads out to the rest of the universe. Light, heat and radiation are the forms of energy that leave the Sun. Light takes about eight minutes to reach us here on Earth.

The energy available here on Earth comes from the Sun. Plants utilize this energy (i.e., the Sun) to perform photosynthesis and, therefore, to survive and produce oxygen. Animals then use this oxygen, as well as consume the plants, for their survival. And, millions of years ago, fossil fuels were formed from decaying plants and animals. As this source of energy is quickly depleted by today's rapid consumption, engineers have searched for ways to sustain our current rate of energy use. Newer technologies, such as solar power (among other alternatives forms of energy), utilize the Sun directly to produce electricity. Engineers play a major role in the design and implementation of technologies such as this.

There is much phenomena associated with the Sun, and most of the activity on its surface directly affects us here on Earth. Sunspots, solar flares, and coronal mass ejections are the main active events that we can observe.

Sunspots lie in active regions on the Sun's surface; they follow the same eleven-year cycle of the Sun, and they fluctuate in number. Sun spots are cooler regions of the sun with temperatures of about 3,700 degrees Kelvin (K), but as hot as 5,700 degrees K directly around the spot. The lifespan of a sunspot can be a few days up to weeks for very large spots. Sunspots are similar to magnets in that they come in pairs: a positive and negative one. These spots produce strong magnetic fields that enter the surface of the Sun and add to the natural field of the Sun produced by the flow of ions and electrons.

Solar flares occur as the Sun releases an extreme amount of magnetic energy. Even with our advanced understanding of the Sun and solar flares, engineers and scientists are still unable to predict when these flares will occur. The energy released from a solar flare is equivalent to millions of hydrogen bombs exploding concurrently. The flares can reach up to 100 million degrees K but generally are between 10 and 20 million degrees K. They occur in the active regions on the Sun's surface (around sunspots) and follow the Sun's eleven-year cycle. The Earth's atmosphere is directly influenced by solar flares. According to NASA, solar flares are the most energetic explosions in the solar system. Eight minutes after erupting from the Sun, the energy reaches the Earth and causes the atmosphere to become ionized and expand. As a result, long distance radio signals are disrupted and satellite orbits are disturbed, with possible damage occurring to their electrical components.

Coronal mass ejections, or CMEs, are similar to solar flares and can occur in the presence or absence of flares. CMEs are large bubbles of gas that are ejected from the Sun over several hours and travel at a speed of 2000 km per second. NASA observes 2-3 CMEs a day during a maximum sunspot cycle. CMEs can have catastrophic effects on the Earth and, similar to solar flares, may include a disruption of power and satellites. Outside the Earth's magnetic field, CMEs can cause damage to electronic equipment and astronauts in space.

Brainstorming: As a class, have the students engage in open discussion. Remind students that in brainstorming, no idea or suggestion is "silly." All ideas should be respectfully heard. Take an uncritical position, encourage wild ideas and discourage criticism of ideas. Have them raise their hands to respond. Write their ideas on the board. Ask the students:

• What tools do engineers and scientists use to view and learn about the Sun? (Possible answers: telescopes, high-powered imaging systems, satellites)
• How big is the Sun? (Answer: Large enough for a million Earths to fit inside it.)
• How far away is the Sun from the Earth? (Answer: 92 million miles)
• How long does it take light to travel from the Sun to the Earth? (Answer: eight minutes)

Idea Web: Ask students to brainstorm a list of activities we could not do if there was no Sun. What effects would the lack of these activities have on our daily lives? Could you live without the Sun? Encourage the students to build off of the other ideas. Have them create the idea web on the chalk/white board.

Pass the Buck: In groups of four, have students brainstorm ideas to design the ultimate renewable energy system. First, assign one student in the group to be the recorder. Then, have someone toss out an idea. Next, another person in the group provides an idea that builds on the first. Go around the group in this fashion until all students have put in enough ideas to put together a design. When they are done, have them share their idea(s) with the class. Encourage the incorporation of any current renewable energy systems (solar power, wind power, etc.) that they have learned about in other classes or past lessons. This can also be a fun exercise as an entire class.