Eclipse

(adsbygoogle = window.adsbygoogle || []).push({}); When three celestial objects become aligned, an eclipse is said to occur. The many eclipse events known to astronomers are of two different types. In the first, the eclipsing body comes between an observer and the eclipsed object. The eclipsed object appears to the observer to be totally or partially covered by the eclipsing object. Eclipses of the second type affect only planets or natural satellites. In this case, the eclipsing body comes between the sun and the eclipsed object. The eclipsed...

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Light

One of the most familiar and important forms of energy is light. Nothing is visible to humans when light is totally absent. But light is even more important for other reasons. Many scientists believe that millions of years ago light from the sun triggered the chemical reactions that led to the development of life on Earth. Without light the living things now on Earth would be unable to survive. Light from the sun provides energy for life on Earth. Plants change the energy of sunlight into food energy. When light rays strike a green plant,...

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Dead Sea

Between Israel and Jordan lies the Dead Sea, a salt lake located on the lowest point of the Earth's surface. Its basin lies some 1,300 feet (400 meters) below sea level, making it the lowest body of water in the world. The lake is about 50 miles (80 kilometers) long and 11 miles (18 kilometers) wide. Its surface area is about 394 square miles (1,020 square kilometers). The Dead Sea extends from north to south in a great depression between rocky cliffs. The depression is a rift valley, caused by the Earth's crust having slipped down between...

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Fungus

Fungi (singular, fungus) are everywhere in the environment—in the soil; in lakes, rivers, and the seas; in the air (some are so tiny that they are carried by currents of wind or on the bodies of insects); and in and on plants and animals, including humans. Along with bacteria, fungi are responsible for the decay of organic matter and the release into the atmosphere of carbon, oxygen, nitrogen, and phosphorus. Many of them are eaten at the dinner table. One of the most beneficial uses of a fungus came with the virtually accidental discovery...

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Mars

As it is visible from Earth without the aid of a telescope, the planet Mars has intrigued stargazers since ancient times. Babylonians mentioned Mars in records from about 3,000 years ago, associating the red planet with their god of death. The modern name Mars is that of the Roman god of war; the planet's two moons, Phobos (Fear) and Deimos (Terror), are named after the sons of Ares, the Greek god of war. Mars passes relatively close to the Earth in its orbit. In addition, it generally has no obscuring layer of clouds, unlike the Earth's other...

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Vitamin

All living things, plant or animal, need vitamins for health, growth, and reproduction. Yet vitamins are not a source of calories and do not contribute significantly to body mass. The plant or animal uses vitamins as tools in processes that regulate chemical activities in the organism and that use basic food elements—carbohydrates, fats, and proteins—to form tissues and to produce energy. Vitamins can be used over and over, and only tiny amounts are needed to replace those that are lost. Nevertheless, most vitamins are essential in the diet...

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Water

Nearly three fourths of the Earth's surface is covered with water. Perhaps the most important liquid in the world, water is usually easy to get from rain, springs, wells, streams, rivers, ponds, and lakes. It fills the vast ocean beds. As vapor, water is also present in the air, where it often condenses into clouds. The bodies of most living things contain a large proportion of water. For example, water comprises about 60 percent of the weight of the human body. Water is necessary for life. Millions of years ago the first forms of life on Earth...

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