The Soviet satellite Sputnik 1, which was launched into space on October 4, 1957, was the first spacecraft to go into orbit around Earth. It had no crew members or animals aboard, but instead contained machines that sent information back to Earth via radio.
The former Soviet Union’s (now Russia) launch of Sputnik prompted the United States to get its first satellite, Explorer 1, into orbit quickly, igniting the so-called space race. This was the two countries’ rivalry over being the “first” in many areas of space exploration. Explorer 1’s test run in December 1957 burned on the ground, but the satellite was successfully launched into orbit around Earth on January 31, 1958.
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.
Farmers and state governments use chemical pesticides to protect their crops from insect pests, weeds, and fungal diseases while they are growing. They also spray their crops with pesticides to prevent rats, mice, and insects from contaminating foods while they are being stored.
While these actions are meant to benefit human health and bring a wide variety of fruits and vegetables to the supermarket, they can also harm people, wildlife, and the environment. This is why there are strict controls in place over their sale and use.
Today, about 3.5 percent of ocean water is salt. When planet Earth was still young, its atmosphere contained a mix of hydrogen chloride, hydrogen bromide, and other gasses from volcanoes. Oceanographers (scientists who study the ocean) believe that some of these gases dissolved in the early ocean, making it salty.
Today, however, most of the salt in the oceans comes from rain. Rain falling on the land dissolves the salts in eroding rocks, and these salts are carried down the rivers and out to sea. The salts accumulate in the ocean as water evaporates to form clouds. The oceans are getting saltier every day, but the rate of increase is so slow that it hard to measure. If the oceans suddenly dried up, there would be enough salt to build a 180-mile- (290-kilometer) tall wall around the equator.
The Earth is not round, but slightly squashed; it’s diameter at the equator (the imaginary line on Earth’s surface that divides Earth into a Northern and a Southern Hemisphere) is about 24 miles (38 kilometers) greater than its diameter at the poles. Why? Because the planet is constantly spinning, forcing material out toward the equator. The Earth’s surface is both smooth and bumpy, with vast oceans, tall mountains, rolling plains, canyons, swamps, and deserts.
The tallest mountain on our planet, Mount Everest in the Himalayas, stands at an altitude of 29,108 feet (8,872 meters), while Africa’s Sahara, the largest desert on Earth, spans over 2.1 million square miles (500,000 square kilometers) of land.
Babies are born with about 300 to 350 bones, but many of these fuse together between birth and maturity to produce an average adult total of 206. Bone counts vary according to the method used to count them, because a structure may be treated as either multiple bones or as a single bone with multiple parts. There are four major types of bones: long bones, short bones, flat bones, and irregular bones. The name of each type of bone reflects the shape of the bone. The shape of the bone also tells about its mechanical function. Bones that do not fall into any of these categories are sesamoid bones and accessory bones.
Cellular, or cell, phones first became available to consumers in the early 1980s, but the technology that made them small and truly portable evolved gradually over the next 10 years or so. By the beginning of the twenty-first century, millions and millions of people in countries all over the world were using cell phones on a daily basis. And it isn’t just adults who enjoy the benefits of completely mobile phone capabilities: in the United States alone, more than 20 percent of teenagers have a cell phone. That translates to at least one in five American teens. The cellular system divides each city into many small cells (a large city can have hundreds). Each cell has its own tower (which contains an antenna as well as transmitters and receivers that send and receive signals). Each tower can handle numerous callers at a given time, and their small size and weaker signal (compared to the radio antennae) means that their signals don’t interfere with those of nearby towers. When you call someone using a cellular phone, your phone is sending and receiving signals via radio waves, invisible bands of energy that work like light rays. In other words, your cell phone is a fancy, high-tech radio. After you dial a friend’s number, your phone must find the closest tower by searching for the strongest signal. Once that signal is located, your phone transmits certain information—like your cell phone number and serial number—that help your service provider make sure you are one of their customers.
Then the mobile telephone switching office (MTSO) finds an available channel where your conversation can take place. The MTSO then completes the connection (all of this happening in a few short seconds) and you are chatting with your friend, without wires or cords to hold you down. If you are sitting in the back seat of the car while talking, and your mom is driving you from one end of town to the other, your call will be switched automatically from one cell tower to the next without any pause in your conversation.
The Sun is extremely hot. The surface of the Sun (or its outer visible layer, called the photosphere) is about 10,000 degrees Fahrenheit (5,537 degrees Celsius)— about 50 times the temperature required to boil water.
The core of the Sun, where solar energy is created, reaches 27 million degrees Fahrenheit (15 million degrees Celsius). It is so intense that nuclear reactions take place there.
Before Lippershey and Galileo, magnification instruments had not been used to investigate objects beyond Earth. Since their time, far more powerful visiblelight telescopes have been developed along with other types of telescopes capable of “seeing” invisible forms of radiation, such as infrared, ultraviolet, radio, X-ray, and gamma-ray. Today’s optical telescopes (made from glass, lenses, or mirrors) are 100 million times more sensitive than Galileo’s telescope. For example, Hawaii’s twin Keck Tele scopes are the world’s largest optical and infrared telescopes. Each stands eight stories tall and weighs 300 tons.
The Hubble Space Telescope, named after astronomer Edwin Hubble and launched into space in 1990, orbits Earth at a speed of 5 miles (8 kilometers) per second, and beams images back to Earth. Because its position is above the atmosphere (which distorts and blocks the light that reaches Earth) it is able to view the universe more thoroughly and clearly than ground-based telescopes.
Yes. Mars, the fourth planet from the Sun, is called the Red Planet. It looks red because the rocks on the surface contain rusted iron. It has an atmosphere with clouds, winds, and dust storms—its red dust floats in the atmosphere and gives the planet a red sky.
Mars, which has two moons, orbits the Sun every 687 days and rotates on its axis once every 24 hours and 37 minutes.