Jupiter, Saturn, Uranus, and Neptune have rings—or thin belts of rocks—around them. Jupiter’s ring is thin and dark, and cannot be seen from Earth. Saturn’s rings are bright, wide, and colorful. Uranus has nine dark rings around it, and Neptune’s rings are also dark, but contain a few bright arcs.
At one time all of the planets, Earth included, had rings. These rings were unstable and the material was either lost in space or collected into the satellites of these planets.
In 1960, astronomers discovered some mysterious space objects and called them quasars because they were discovered to be a strong source of radio waves. In fact, the term “quasar” comes from the words “quasi-stellar radio source.” Quasars are sources of light or radio waves, just like galaxies, that emit enormous amounts of energy.
They are the most distant objects scientists have discovered. They are very bright (as bright as hundreds of galaxies, burning with the energy of 1 trillion Suns) and much smaller than most galaxies. Today, many astronomers refer to these objects as quasi-stellar objects, or QSOs.
Internet search engines are like computerized card catalogs at libraries. Viewed through a Web browser with an Internet connection, they provide a hyperlinked listing of locations on the World Wide Web according to the requested keyword or pattern of words submitted by the searcher. Search engines use computer software called “spiders” or “bots” to search out, inventory, and index Web pages automatically.
The spiders scan each Web page’s content for words and the frequency of words, then stores that information in a database. When the user submits words or terms, the search engine returns a list of sites from the database and ranks them according to the relevancy of the search terms.
Several different factors determine how big a person will grow. The most important one is heredity, the passing of physical traits from parents to children. When you began as a single fertilized cell, your mother and father each contributed half the genes—coded chemical information—needed for you to live and grow. These genes are responsible for your physical traits, like the color of your eyes and hair, how your body will be shaped, and how tall you will become. That is why children look a lot like their parents, or even their grandparents: they have inherited family characteristics that may have been passed on for several generations. If your parents are big or tall, chances are good that you will be big or tall, too. The average height of a woman in the United States is about 5 feet, 4 inches (1.6 meters), and the average height for an American man is 5 feet, 9 inches (1.75 meters).
In spite of genetic coding, certain conditions can keep people from growing as large as their genes say they should. Bad nutrition keeps a body from reaching its maximum size. Poor health and disease do the same. That is why people who lived in generations before us, when food was sometimes scarce and health care was poor, were quite a bit smaller than we are today. Taking good care of your body, then, helps it become the best it can be.
After a victory on a battlefield, the ancient Greeks would build a monument dedicated to a chosen god, which they called a “trophy.” These trophies were made of limbs stripped from the dead enemy soldiers and then hung on a tree or pillar, a ritual that is kept alive by modern “trophy hunters,” who celebrate their victory over an unarmed animal by hanging its head on the wall.
Be grateful for the Stanley Cup.
Airplanes function according to a complex mix of aerodynamic principles—theories that explain the motion of air and the actions of bodies moving through that air. Airplanes get their power from engines. Small planes generally use piston engines, Which turn propellers that push aircraft through the air in the same way that boat propellers push vessels through water. But bigger planes use jet engines, powered by burning fuel. These engines expel great amounts of air that thrust a plane forward and up. An airplane must be in constant motion—its wings slicing through rushing air to create lift—in order to stay up; moving air is also required to steer it. In order to get enough lift to rise into the air on takeoff, an airplane has to travel along the ground first at great speed.
Airplanes are able to lift into the air and stay there because of the shape of their wings. An airplane wing is flat on the bottom and curved on the top. When a plane’s engines push it forward, air divides to travel around its wings. The air that passes over the larger curved top moves faster than the air that passes under the flat bottom. The faster-moving air on top becomes thinner and has lower pressure than the air below, which pushes the wing up. Uneven air pressure caused by the shape of an airplane’s wings, then, creates a force called lift, which allows an aircraft to fly.
Our muscles, which make up about half of our body mass, control the way the body moves. Muscles work together all the time, whether we are actively playing sports, or quietly reading and writing. Muscles lie in bands just beneath the surface of the skin. A muscle is made up of thousands of fibers bundled together within a protective sheath that consists of blood vessels and nerves. These nerves can be up to 12 inches (30 centimeters) long. A muscle becomes stronger when you work it, which is why people Who regularly exercise have more defined muscle tone than those Who do not exercise. There are about 660 muscles in the human body. The three types of muscle tissue are skeletal, cardiac, and smooth. The main and most unique characteristic of muscle tissue is its ability to contract, or shorten, making some type of movement possible.
Skeletal muscles hold the bones together, and are often called “voluntary” muscles because the brain controls them. The cardiac muscle, which is found only in the heart, contracts to send blood from the heart into the arteries. The brain sends signals to the cardiac muscle to speed up or slow down its contractions, called the heartbeat. Smooth muscles, located in the internal organs such as the stomach and intestines, help these organs or tissues do their job, such as help you digest and eliminate your food.
The hectare (abbreviated ha) is a unit of area equal to 10,000 square meters and used exclusively for measuring land. To get a sense of how big this is, imagine a football field. A football field is almost exactly 100 meters from one end line to the opposite goal line.
Imagine a square of that length on each side, and you’ve got an area of one hectare. There are 100 hectares in one square kilometer, so one square kilometer is the same area as a square that is ten football fields on one side.
According to many religions based on Judaism and Christianity, heaven is a state of existence where a person’s spirit is at last united with God forever. In a number of Christian religions, heaven is believed to be the reward for people who have lived good lives according to certain rules of thought and behavior that God has made known through scriptures (sacred writings, like the Bible) and through the teachings of churches and religious leaders. (Those who have not followed these rules, it is believed by many, go to a place of punishment known as hell.) Many Christians believe that at the end of the world their human forms will be resurrected in a perfect state—just as the body of Jesus Christ was, when he arose from the dead on Easter morning—and join their souls or spirits in heaven for eternity.
This idea has led to the concept that heaven is an actual place—located above—with physical characteristics. Over the centuries, through pictures and writings, people have tried to create images of heaven, imagining a place of perfect happiness perched atop fluffy white clouds. It has often been portrayed as a place full of things that would bring happiness on Earth, possessing, for instance, pearly gates and streets of gold.
Scientists often compare Earth to an onion because the planet is made up of many layers of rocks of different densities. On the outside, there is a think crust of hard, cold rock, which is about 4 miles (7 kilometers) thick under the oceans and 22 miles (35 kilometers) thick under the continents. The crust—the layer we live on—surrounds a hard, rocky surface that marks the top of the mantle, called the lithosphere. Most of Earth is made of its mantle, Which goes almost halfway down to Earth’s center.
At the very center is Earth’s core, which has a center of solid iron and nickel about the size of the Moon (called the inner core) and a molten exterior (called the outer core). The temperature of Earth increases about 36 degrees Fahrenheit (2.2 degrees Celsius) for every 0.62 miles (1 kilometer) down you go, reaching temperatures as high as 11,000 degrees Fahrenheit (6,093 degrees Celsius) at its center.