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.
There is no way specific way to place an order for a baby brother or a baby sister. The gender (boy or girl) of a baby is determined by whether the father’s fertilizing sperm has an X or a Y chromosome. An X chromosome will lead to a girl, and a Y to a boy. (Mothers always contribute an X chromosome.) Although scientific methods are available to help parents organize their chromosomes and take advantage of the fact that the “boy” sperm has less DNA than “girl” sperm, they can be expensive and unreliable. One method, called the Shettles method, recommends that if parents want a girl, they should plan to make a baby right around the time of ovulation.
At this time, the egg is as far away as possible from the incoming sperm so the long-distance runners of the sperm world, the X sperm, have a better chance of making it to the egg. For a boy, the method suggests that parents plan to make a baby about two to four days after ovulation. That way, the short-distance sprinting Y sperm can make it to the egg first. Many doctors say that although this method is based in science, it is no guarantee that a couple will have a baby boy or a baby girl.
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.
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.
Cotton, which comes from flowering Gossypium plants, is a key vegetable fiber used for making clothes, and oil from its seeds can be used in cooking or for making soap. The cotton plant grows in 17 states that make up the U.S. “Cotton Belt”: California, Arizona, New Mexico, Texas, Oklahoma, Arkansas, Missouri, Mississippi, Alabama, Louisiana, Florida, Tennessee, North Carolina, South Carolina, Virginia, Georgia, and Kansas. In the United States, where cotton is no longer picked by hand, machines called pickers or strippers harvest the crops.
Cotton-picking machines have spindles that pick (twist) the seed cotton from the burrs that are attached to plants’ stems. Doffers— a series of circular rubber pads—then remove the seed cotton from the spindles and knock the seed cotton into a conveying system. Conventional cotton stripping machines use rollers equipped with alternating bats and brushes to knock the fluffy white bolls, which contain seeds and hairs, from the plants into a conveyor. After harvest, most of the cotton is pressed into large blocks for storage. These cotton bundles are then transported to the cotton gin, a machine that pulls out the seeds from the cotton bolls.
Absolutely. Being bitten by a plant-eating dinosaur such as Brachiosaurus, with its 52 chisel-like teeth, would certainly hurt! The bite of a Parasaurolophus, with its interlocking rows of teeth, might take off your fingers. In the Iguanodon, numerous sharp teeth were set in rows in the upper and lower jaws, and at steep angles to each other.
When the teeth were pressed together, the upper jaw was forced outward, creating a grinding motion between the teeth and its meal of crushed plant tissue.
As the young red blood cell grows and takes on an adult form in the marrow of the bone, it loses its nucleus, and it increases its production of hemoglobin. Hemoglobin is the red pigment, or color of blood, and contains iron, combined with protein. (Oxygen combined with iron is red; the more oxygen iron has bound to it, the redder it is.)
When blood passes through the lungs, oxygen attaches itself to the hemoglobin of the red cells. From there, the red cells carry the oxygen through the arteries and the capillaries to all other cells of the body. The arteries appear reddish because the iron in the blood gives up its oxygen to the cells that need it as the red blood cells travel throughout the body. By the time the blood is back on its way to the heart and then to the lungs it has less than half as much oxygen as it did before. The veins, therefore, do not get as much oxygen as the other tissues and they appear bluish.
According to the National Aeronautics and Space Administration (NASA), Which is in charge of space exploration and scientific discovery for the United States, the Hubble transmits about 120 gigabytes of science data every week. That’s equal to about 3,600 feet (1,097 meters) of books on a shelf. The growing collection of pictures and data is stored on magneto-optical disks. Among its many discoveries, Hubble has revealed the age of the universe to be about 13 to 14 billion years, which is a more accurate estimate than the Big Bang range of between 10 to 20 billion years.
Hubble also played a key role in the discovery of dark energy, a mysterious force that causes the expansion of the universe to accelerate. Hubble has shown scientists galaxies in “toddler” stages of growth, helping them understand how galaxies form. It found protoplanetary disks, clumps of gas and dust around young stars that likely function as birthing grounds for new planets. It discovered that gamma-ray bursts—strange, incredibly powerful explosions of energy—occur in far-distant galaxies when massive stars collapse.
The combine harvester saves the farmers time and labor. Before modern machinery, harvesting crops was a painstaking process. Gathering and removing mature plants from the field had to be done by hand. Farm workers used sharp-bladed, long-handled scythes and curved sickles to cut down cereal crops like wheat. Even the fastest reaper could only clear about a third of an acre a day. Because rain could ruin harvested wheat, workers called sheaf-makers quickly tied it into bundles, so that it could be safely stored if the weather turned stormy. During the long winter months farm workers used jointed wooden tools called flails to thresh or beat the dried wheat in order to separate its edible grain seeds from its stalks.
But in 1786 a machine that threshed wheat by rubbing it between rollers was invented, replacing human threshers. And around 1840 a reaping machine—whose revolving wheel pressed grain stalks against a sharp blade that cut them down— replaced human harvesters. Today, farm machines called combine harvesters do this work in much the same way. These machines are very efficient and combine all three jobs of cutting, collecting, and threshing a crop. A single combine harvester can process five acres of wheat in less than an hour!
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.