The sun is the closest star to Earth, and even at a distance of 150 million kilometers its gravitational pull holds the planet in orbit. It radiates light and heat, or solar energy, making it possible for life to exist on Earth. Plants need sunlight to grow, and animals, including humans, (18) __________. Without heat from the sun, Earth would freeze, and there would be no winds, ocean currents, or clouds needed to transport water around the globe. Solar energy has existed as long as the sun, about 4.6 billion years, (19) __________. Developed over 11,000 years ago, agriculture used solar energy to produce crops and preserve food. Intentional planting in vast, sunny areas increased yields, and drying food in the sun prevented it from spoiling, creating surpluses that supported growing populations and structured societies. Early urban societies positioned buildings to face south, used windows and skylights, and chose materials with thermal mass, elements of solar architecture that are now aided by computer programs. Greenhouses convert sunlight to heat to grow plants out of season, and solar energy can also cook food. (20) __________. Solar technology can even support healthcare, as solar autoclaves heat water to sterilize instruments in rural clinics. Solar power converts sunlight into electricity through photovoltaics and concentrating solar thermal power. Solar cells powered Vanguard I in 1958 and now run everything from calculators to homes and commercial buildings. It was not until the first couple of decades of the 21st century that (21) __________, alongside the push to respond to human caused climate change. Besides generating electricity, solar energy can also make water potable through solar disinfection. Solar disinfection, (22) __________. Still, solar power is intermittent, takes up space, and can displace plants, wildlife, and communities, while producing panels can harm environments and supply chains. Even so, the sun offers an abundance of free and clean energy when governments and communities work to lessen these drawbacks, and relying on renewable energy is not only possible, but critical for addressing climate change. [Adapted from https://education.nationalgeographic.org/resource/power-sun/] |
