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Every two years as the Olympic Games begin, we hear about athletes using or at least being tested for performance-enhancing drugs. Every time the Tour de France rolls around, there's talk of possible doping. Sometimes, competitors raise the question when one athlete does particularly well. Other times, tests catch athletes with drugs in their systems. The practice of using artificial substances or methods to enhance athletic performance is called doping. Doping has become such a great concern that the United States formed an Anti-Doping Agency.

Why Some Athletes Use DrugsAthletes face enormous pressure to excel in competition. They also know that winning can reap them more than a gold medal. A star athlete can earn a lot of money and a lot of fame, and athletes only have a short time to do their best work. Athletes know that training is the best path to victory, but they also get the message that some drugs and other practices can boost their efforts and give them a shortcut, even as they risk their health and their athletic careers.

As far back as ancient Greece, athletes have often been willing to take any preparation that would improve their performance. But it appears that drug use increased in the 1960s. One well-publicized incident happened at the Seoul Olympics in 1988 when sprinter Ben Johnson tested positive for anabolic steroids and was stripped of his gold medal. Athletes may also misuse drugs to relax, cope with stress or boost their own confidence. Athletes may have several reasons for using performance-enhancing drugs. An athlete may want to: Build mass and strength of muscles and/or bones Increase delivery of oxygen to exercising tissues Mask pain Stimulate the body Relax Reduce weight Hide use of other drugs

A third of reef-building corals worldwide are threatened with extinction due to climate change and water pollution, according to the first global assessment on the marine creature by 39 scientists.

Destructive fishing and the degradation

"When corals die off, so do the other plants and animals that depend on coral reefs for food and shelter, and this can lead to the collapse of entire ecosystems," he added.

end of the spectrum are the reds and oranges. These gradually shade into yellow, green, blue, indigo and violet. The colors have different wavelengths, frequencies, and energies. Violet has the shortest wavelength in the visible spectrum. That means it has the highest frequency and energy. Red has the longest wavelength, and lowest frequency and energy. LIGHT IN THE AIR Light travels through space in a straight line as long as nothing disturbs it. As light moves through the atmosphere, it continues to go straight until it bumps into a bit of dust or a gas molecule. Then what happens to the light depends on its wave length and the size of the thing it hits. Dust particles and water droplets are much larger than the wavelength of visible light. When light hits these large particles, it gets reflected, or bounced off, in different directions. The different colors of light are all reflected by the particle in the same way. The reflected light appears white because it still contains all of the same colors. Gas molecules are smaller than the wavelength of visible light. If light bumps into them, it acts differently. When light hits a gas molecule, some of it may get absorbed. After awhile, the molecule radiates (releases, or gives off) the light in a different direction. The color that is radiated is the same color that was absorbed. The different colors of light are affected differently. All of the co

d after Lord John Rayleigh, an English physicist, who first described it in the 1870's.) WHY IS THE SKY BLUE? The blue color of the sky is due to Rayleigh scattering. As light moves through the atmosphere, most of the longer wavelengths pass straight through. Little of the red, orange and yellow light is affected by t

As you look closer to the horizon, the sky appears much paler in color. To reach you, the scattered blue light must pass through more air. Some of it gets scattered away again in other directions. Less blue light reaches your eyes. The color of the sky near the horizon appears paler or white.