ThisisSCIENCE

This is SCIENCE UN THE NEWS, in VOA Special English. I'm Steve Ember.undelete files This week our program is about a mystery as old as time. Bob Doughty and Sarah Long tell about the mystery of time.If you can read a clock, you can know the time of day. hard drive repairBut no one knows what time itself is. We cannot see it. We cannot touch it. We cannot hear it. We know it only by the way we mark its passing.Digital photo repairFor all our success in measuring the smallest parts of time, time remains one of the great mysteries of the universe.One way to think about time is to imagine a world without time. There could be no movement,desktop recovery because time and movement cannot be separatedA world without time could exist only as long as there were no changes. For time and change are linked. We know that time has passed when something changes.email recovery softwareIn the real world -- the world with time -- changes never stop. Some changes happen only once in a while, like an eclipse of the moon. Others happen repeatedly, like the rising and setting of the sun. Humans always have noted natural events that repeat themselves. When people began to count such events, they began to measure time. In early human history, the only changes that seemed to repeat themselves evenly were the movements of objects in the sky. The most easily seen result of these movements was the difference between light and darkness.recover deleted filesThe sun rises in the eastern sky, producing light. It moves across the sky and sinks in the west, causing darkness. The appearance and disappearance of the sun was even and unfailing. The periods of light and darkness it created were the first accepted periods of time. We have named each period of light and darkness -- one day.People saw the sun rise higher in the sky data recovery crackduring the summer than in winter. They counted the days that passed from the sun's highest position until it returned to that position. They counted three hundred sixty-five days. We now know that is the time Earth takes to move once around the sun. We call this period of time a year.Early humans also noted changes in the moon. As it moved across the night sky, they must have wondered. Why did it look different every night? Why did it disappear? Where did it go Even before they learned the answers to these questions, they developed a way to use the changing faces of the moon to tell time.Twindows partition recoveryhe moon was "full" when its face was bright data recovery hard diskand round. The early humans counted the number of times the sun appeared between full moons. They learned that this number always remained the same -- about twenty-nine suns. Twenty-nine suns equaled one moon. photo recovery softwareW 2000 e now know this period of time as one month.Early humans hunted animals and gathered wild plants. They moved in groups or tribes from place to place in search of food. rebuild raidThen, people learned to plant seeds and grow crops. They learned to use animals to help them work, and for food.They found they no longer needed to move from one place to another to survive.As hunters, people did not need a way to measure time. As farmers, however, they had to plant crops in time to harvest them before winter. They had to know when the file recovery softwareseasons would change. So, they developed calendars.No one knows when the first calendar was developed. But it seems possible that it was based on moons, or lunar months.files recoveryWhen people started farming, the wise men of the tribes became very important. They studied the sky. They gathered enough information so they could know when the seasons would change. They announced when it was time to plant crops.The divisions of time we use today file recovery deletedwere developed in ancient Babylonia four thousand years ago. Babylonian astronomers believed the sun moved around the Earth every three hundred sixty-five days. pc file recoveryThey divided the trip into twelve equal parts, or months. Each month was thirty days. Then, they divided each day into twenty-four equal parts, or hours. data recovery downloadThey divided each hour into sixty minutes, and each minute into sixty seconds.Humans have used many devices to measure time. The sundial was one of the earliest and simplest.A sundial measures the movement of the sun across the sky each day. It has a stick or other object that rises above a flat surface. The stick, blocking sunlight, creates a shadow.ntfs file recovery As the sun moves, so does the shadow of the stick across the flat surface. Marks on the surface show the passing of hours, and perhaps, minutes.The sundial works well only when the sun is shining. outlook express email So, other ways were invented to measure the passing of time. One device is the hourglass. recover emailsIt uses a thin stream of falling sand to measure time. The hourglass is shaped like the number eight --- wide at the top and bottom, but very thin in the middle. In a true "hour" glass, it wholesale jordanstakes exactly one hour for all the sand to drop from the top to the bottom through a very small opening in the middle. When the hourglass is turned with the upside down, it begins to mark the passing of another hour.