269 résultats pour "earth"
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Earth (planet).
Milky Way to complete one revolution around the Galaxy’s center. Earth’s axis of rotation is inclined (tilted) 23.5° relative to its plane of revolution around the Sun. This inclination of the axis creates the seasons and causes the height of the Sun in the sky at noon to increase and decrease as the seasons change. The Northern Hemisphere receives the most energy from the Sun when it is tiltedtoward the Sun. This orientation corresponds to summer in the Northern Hemisphere and winter in the S...
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Earth (planet) - astronomy.
Milky Way to complete one revolution around the Galaxy’s center. Earth’s axis of rotation is inclined (tilted) 23.5° relative to its plane of revolution around the Sun. This inclination of the axis creates the seasons and causes the height of the Sun in the sky at noon to increase and decrease as the seasons change. The Northern Hemisphere receives the most energy from the Sun when it is tiltedtoward the Sun. This orientation corresponds to summer in the Northern Hemisphere and winter in the S...
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EARTH, ATMOSPHERE AND SPACE
oxygen, which has three instead of the usual two atoms in itsmolecules. The ozone layer also plays a vital role in helpinglife on Earth. It does so by filtering out from sunlight most ofthe harmful ultraviolet rays. These are the rays that causesunburn. Without the ozone layer, the intensity of ultraviolet radiationwould have a devastating effect on both plant and animal life.That is why the observed thinning of the ozone layer because ofatmospheric pollution is so worrying. 3.Into spaceThe air...
- Gaia (Gaea, Ge; Earth) Greek The personification of the Earth Mother in Greek mythology; known to the Romans as Tellus.
- Earth Mother A symbol in many ancient myth systems of the Earth, the source of all life and the power to create life.
- Earth Day.
- Earth Mother
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Prometheus (Forethought) Greek One of the
Titans, descended from the Earth Mother (Gaia)
and the Sky Father (Uranus); son of Iapetus and
one of the daughters of Oceanus, possibly Clymene;
brother of Atlas and Epimetheus; father of Deucalion.
knew he was being tricked, Zeus decided to keep the knowledge of fire-making from humankind. Prometheus, undaunted, stole fire from heaven, or from the forge of the smith-god, Hephaestus, and took it to Earth hidden in the hollow stalk of the fennel plant. He then began to teach people all the uses of fire—how to make tools and fashion metal, how to build, and how to cook. He also taught people how to sow and reap, and how to use herbs for healing. Prometheus, Bound and Unbound - Mythology. Pro...
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- Nicolaus Copernicus I INTRODUCTION Nicolaus Copernicus (1473-1543), Polish astronomer, best known for his astronomical theory that the sun is at rest near the center of the universe, and that the earth, spinning on its axis once daily, revolves annually around the sun.
- Rhea (Earth) Greek A Titan, the mother of the great ruling gods of Olympus.
- Pandora (All-giving) Greek The first woman to appear on Earth, according to Greek mythology.
- Cronus (Kronus) Greek A Titan, the son of Uranus (Heaven) and Gaia (Earth).
- Typhon (Typhoeus) Greek A hundred-headed monster whose parents were Gaia (Earth) and Tartarus.
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Astrobiology - astronomy.
water to help reactions along. American chemists Stanley Miller and Harold Urey tested part of Oparin and Haldane’s hypothesis in the early 1950s by simulating conditions of the early Earth. In whathas become known as the Miller-Urey experiment, the two scientists connected two flasks with a loop of glass tubing that allowed the gases to pass between the flasks.They filled the upper flask with methane, ammonia, and hydrogen—components thought to have been in the early atmosphere. They filled the...
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Hercules (mythology)
I
INTRODUCTION
Pollaiuolo's Hercules et Antaeus
In a wrestling match, Hercules triumphed over the mighty giant Antaeus, who received his strength from his mother, the
Earth goddess Gaia.
Pollaiuolo’s Hercules and the HydraAmong his 12 labors, the mythological hero Hercules had to kill the nine-headed Hydra. Each time Hercules cut off onehead, two more grew in its place. Hercules solved the problem by, as soon as he cut off one head, burning with a torchthe spot where it had been to stop its regrowth. Hercules and the Hydra (about 1460, Uffizi, Florence, Italy) was paintedby Italian artist Antonio Pollaiuolo. Hercules is shown wearing the skin of the Nemean lion, which he had kil...
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Venus (planet) - astronomy.
level winds circle the planet at 360 km/h (225 mph), making a complete rotation in only four days. These winds are said to super-rotate because they travel muchfaster than the rotation of the planet itself. These high-speed winds cover the planet completely, blowing toward the west at virtually every latitude from equator topole. The motions of descending probes, however, have shown that the bulk of Venus’s tremendously dense atmosphere, closer to the planet’s surface, is almoststagnant. From th...
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Artificial Satellite - astronomy.
The first stage of a multistage rocket consists of rocket engines that provide a huge amount of force, or thrust. The first stage lifts the entire launch vehicle—with itsload of fuel, the rocket body, and the satellite—off the launch pad and into the first part of the flight. After its engines use all their fuel, the first stage portion of therocket separates from the rest of the launch vehicle and falls to Earth. The second stage then ignites, providing the energy necessary to lift the satellit...
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Moon - astronomy.
B Volcanic Features Maria, domes, rilles, and a few craters display indisputable characteristics of volcanic origin. Maria are plains of dark-colored rock that cover approximately 40 percent ofthe Moon's visible hemisphere. The maria formed when molten rock erupted onto the surface and solidified between 3.16 billion and 3.96 billion years ago. This rockresembles terrestrial basalt, a volcanic rock type widely distributed on Earth, but the rock that formed the maria has a higher iron content an...
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Extrasolar Planets - astronomy.
When a planet passes in a front of the star it orbits—an event called a transit—it causes a small dip in the brightness of the star. Measuring the slight change in thebrightness can be used not only to directly detect a planet, but to determine its size and orbit. However, the planet needs to orbit in a plane that lies in a telescope’sline of sight on the star. Despite long odds, Earth-based telescopes have detected and studied a few exoplanets using this method. The first space telescope design...
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Planetary Science - astronomy.
III ORIGINS AND COMPOSITIONS OF PLANETS Astronomers believe that planetary systems are formed of elemental materials that were created in the interiors of giant stars. Some of this material comes from giantstars that shed material into space as they age. Most of the matter to form planets, however, comes from stars that explode as supernovas and spread debris enrichedwith the heavier chemical elements into space. According to the currently accepted views, the most likely first stage in the evo...
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Gravitation
I
INTRODUCTION
Gravitation, the force of attraction between all objects that tends to pull them toward one another.
precise observations possible, and Galileo was one of the first to use a telescope to study astronomy. In 1609 Galileo observed that moons orbited the planet Jupiter, afact that could not reasonably fit into an earth-centered model of the heavens. The new heliocentric theory changed scientists' views about the earth's place in the universe and opened the way for new ideas about the forces behind planetarymotion. However, it was not until the late 17th century that Isaac Newton developed a theory...
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Gravitation - astronomy.
precise observations possible, and Galileo was one of the first to use a telescope to study astronomy. In 1609 Galileo observed that moons orbited the planet Jupiter, afact that could not reasonably fit into an earth-centered model of the heavens. The new heliocentric theory changed scientists' views about the earth's place in the universe and opened the way for new ideas about the forces behind planetarymotion. However, it was not until the late 17th century that Isaac Newton developed a theory...
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Geography - geography.
A Collecting Data Geographers may collect data in the field or from secondary sources, such as censuses, statistical surveys, maps, and photographs. Advances made since World War II(1939-1945) in the use of aerial photography, including the use of special films, and in techniques for obtaining three-dimensional views of the landscape from the air haveenabled geographers to perform more detailed studies of the earth and its resources ( see Aerial Survey). Geographers also have made use of radar...
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Geography - Geography.
Geographers have developed a standard pattern of map symbols for identifying such cultural features as homes, factories, and churches; dams, bridges, and tunnels;railways, highways, and travel routes; and mines, farms, and grazing lands. C Analyzing Geographic Information Techniques that use mathematics or statistics to analyze data are known as quantitative methods. The use of quantitative methods enables geographers to treat a largeamount of data and a large number of variables in an objectiv...
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Mercury (planet) - astronomy.
In 1991 powerful radio telescopes on Earth revealed signs of possible deposits of ice in the polar regions of Mercury. These ice deposits occur in areas where sunlightnever falls, such as crater bottoms near both of the planet’s poles. Similar ice deposits may have been found during the 1990s near the poles of the Moon by theClementine and Lunar Prospector spacecrafts. The ice on Mercury likely comes from comets or water-bearing meteorites that have hit Mercury over the planet’s historyup throug...
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Astronomy - astronomy.
Telescopes may use either lenses or mirrors to gather visible light, permitting direct observation or photographic recording of distant objects. Those that use lenses arecalled refracting telescopes, since they use the property of refraction, or bending, of light ( see Optics: Reflection and Refraction ). The largest refracting telescope is the 40-in (1-m) telescope at the Yerkes Observatory in Williams Bay, Wisconsin, founded in the late 19th century. Lenses bend different colors of light by d...
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Ice Ages.
B Future Ice Ages The record of previous glacial activity is the best indicator for future ice ages. Scientists examine the evidence for the numerous 100,000-year glacial-interglacial cycleswithin the present ice age to attempt a forecast of future ice ages. Since all previous ice ages lasted tens of millions of years, our present ice age will likely continue fora considerable amount of time. Each glaciation begins slowly and may take 80,000 years or more to reach its maximum extent. A rapid me...
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History of Astronomy - astronomy.
Egypt, the Sun was directly overhead at noon. On the same date and time in Alexandria, Egypt, the Sun was about 7 degrees south of zenith. With simple geometryand knowledge of the distance between the two cities, he estimated the circumference of the Earth to be 250,000 stadia. (The stadium was a unit of length, derivedfrom the length of the racetrack in an ancient Greek stadium. We have an approximate idea of how big an ancient Greek stadium was, and based on that approximationEratosthenes was...
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Comet - astronomy.
may exceed the planet Jupiter in size, however. Observations from telescopes on Earth and in space indicate that most of the gases in the coma and tail of a comet are fragmentary molecules, or radicals, of the mostcommon elements in space: hydrogen, carbon, nitrogen, and oxygen. The radicals, for example, of CH, NH, and OH may be broken away from the stable molecules CH 4 (methane), NH 3 (ammonia), and H 2O (water), which may exist as ices or more complex, very cold compounds in the nucleus. Al...
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Mars (planet) - astronomy.
The Martian core is probably much like Earth’s, consisting mostly of iron, with a small amount of nickel. If other light elements, particularly sulfur, exist there as well, thecore may be larger than presently thought. From studying Earth’s magnetic field and core, scientists theorize that the motions of the liquid rock in Earth’s core generateits magnetic field. Mars does not have a significant magnetic field, so scientists believe that Mars’s core is probably solid. However, spacecraft data in...
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Jupiter (planet) - astronomy.
Beneath the supercritical fluid zone, the pressure reaches 3 million Earth atmospheres. At this depth, the atoms collide so frequently and violently that the hydrogenatoms are ionized—that is, the negatively charged electrons are stripped away from the positively charged protons of the hydrogen nuclei. This ionization results in asea of electrically charged particles that resembles a liquid metal and gives rise to Jupiter’s magnetic field. This liquid metallic hydrogen zone is 30,000 to 40,000 k...
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Space Exploration - astronomy.
to produce 250,000 newtons (56,000 lb) of thrust. The Germans launched thousands of V-2s carrying explosives against targets in Britain and The Netherlands. Whilethey did not prove to be an effective weapon, V-2s did become the first human-made objects to reach altitudes above 80 km (50 mi)—the height at which outer spaceis considered to begin—before falling back to Earth. The V-2 inaugurated the era of modern rocketry. A2 Early Artificial Satellites During the years following World War II, the...
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Meteorology.
to find the corresponding relative humidity and dew-point temperature. III SPECIAL METEOROLOGICAL INSTRUMENTS Meteorologists have developed several sophisticated instruments that measure multiple physical characteristics of the air simultaneously and at more than one location.The most important of these special instruments are radiosondes, Doppler radar, and weather satellites. A Radiosonde A radiosonde measures air temperature, air pressure, and humidity from the earth’s surface up to an alt...
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Map - Geography.
Often only southeast slopes are hachured or shaded, giving somewhat the effect of a bird's-eye view of the area illuminated by light from the northwest. Shadings orcarefully drawn hachures, neither of which give elevations, are more easily interpreted than contour lines and are sometimes used in conjunction with them for greaterclarity. IV MAP PROJECTIONS For the representation of the entire surface of the earth without any kind of distortion, a map must have a spherical surface; a map of this...
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Neptune (planet) - astronomy.
The gaseous atmosphere of Neptune contains hydrogen, helium, and about 3 percent methane. It extends about 5,000 km (about 3,000 mi) above the planet’s ocean.Light reflected from Neptune’s deep atmosphere is blue, because the atmospheric methane absorbs red and orange light but scatters blue light. In 1998 astronomersalso identified molecules of methyl in Neptune’s atmosphere. Methyl molecules each contain one carbon atom and three hydrogen atoms. Methyl molecules are knownas hydrocarbon radical...
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From Bulfinch's Mythology: Prometheus and Pandora - anthology.
The world being thus furnished with inhabitants, the first age was an age of innocence and happiness, called the Golden Age. Truth and right prevailed, though not enforced by law, nor was there any magistrate to threaten or punish. The forest had not yet been robbed of its trees to furnish timbers for vessels, nor had men builtfortifications round their towns. There were no such things as swords, spears, or helmets. The earth brought forth all things necessary for man, without his labour inplo...
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Asteroid - astronomy.
Asteroids of the S type, related to the stony iron meteorites, make up about 15 percent of the total population of asteroids that can be seen from Earth. Much rarer arethe M-type objects, corresponding in composition to the meteorites known as “irons.” These objects are made up of an iron-nickel alloy and may represent the cores ofbodies that were large enough to differentiate into layers and to melt deep inside. Their rocky outer layers may have been removed by impacts with other asteroids . A...
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Sun - astronomy.
A The Sun’s Place in the Milky Way The Milky Way Galaxy contains about 400 billion stars. All of these stars, and the gas and dust between them, are rotating about a galactic center. Stars that arefarther away from the center move at slower speeds and take longer to go around it. The Sun is located in the outer part of the galaxy, at a distance of 2.6 × 10 17 km (1.6 × 10 17 mi) from the center. The Sun, which is moving around the center at a velocity of 220 km/s (140 mi/s), takes 250 million y...
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Apollo Program - astronomy.
Moon’s orbit; rendezvousing and docking with the CSM; and finally, setting a course home to Earth. On return to Earth, the spacecraft was slowed by drag from Earth’satmosphere and by parachutes (just before splashdown), before landing in the ocean. The transit time to and from the Moon was approximately three days each way.Depending on the specific mission, the time in lunar orbit ranged from less than one day for Apollo 8 to over six days for the final three missions, and the time on thelunar s...
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Apollo Program - U.
Moon’s orbit; rendezvousing and docking with the CSM; and finally, setting a course home to Earth. On return to Earth, the spacecraft was slowed by drag from Earth’satmosphere and by parachutes (just before splashdown), before landing in the ocean. The transit time to and from the Moon was approximately three days each way.Depending on the specific mission, the time in lunar orbit ranged from less than one day for Apollo 8 to over six days for the final three missions, and the time on thelunar s...
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Geology.
terminology. Today the geologic time scale is generally agreed upon and used by scientists around the world, dividing time into eons, eras, periods, and epochs. Everyfew years, the numerical time scale is refined based on new evidence, and geologists publish an update. Geologists use several methods to determine geologic time. These methods include physical stratigraphy, or the placement of events in the order of their occurrence,and biostratigraphy, which uses fossils to determine geologic time...
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Cosmology - astronomy.
In 1917 American scientist Harlow Shapley measured the distance to several groups of stars known as globular clusters. He measured these distances by using amethod developed in 1912 by American astronomer Henrietta Leavitt. Leavitt’s method relates distance to variations in brightness of Cepheid variables, a class of starsthat vary periodically in brightness. Shapley’s distance measurements showed that the clusters were centered around a point far from the Sun. The arrangement of theclusters was...
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Greenhouse Effect.
addition, humans cut down huge tracts of trees for lumber or to clear land for farming or building. This process, known as deforestation, can both release the carbonstored in trees and significantly reduce the number of trees available to absorb carbon dioxide. As a result of these human activities, carbon dioxide in the atmosphere is accumulating faster than Earth’s natural processes can absorb the gas. By analyzing airbubbles trapped in glacier ice that is many centuries old, scientists have d...
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Biodiversity.
a common molecule, ribonucleic acid (RNA), and most also have deoxyribonucleic acid (DNA). These molecules direct the production of proteins—molecules responsiblefor the structure and function of virtually all living cells. This is the evolutionary chain of life. All species are descended from a single common ancestor. From that ancient single-celled microbe, all inherited RNA. As time goesby, species diverge and develop their own peculiar attributes, thus making their own contribution to biodiv...
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Biodiversity - biology.
a common molecule, ribonucleic acid (RNA), and most also have deoxyribonucleic acid (DNA). These molecules direct the production of proteins—molecules responsiblefor the structure and function of virtually all living cells. This is the evolutionary chain of life. All species are descended from a single common ancestor. From that ancient single-celled microbe, all inherited RNA. As time goesby, species diverge and develop their own peculiar attributes, thus making their own contribution to biodiv...
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Relativity
I
INTRODUCTION
Albert Einstein
In 1905 German-born American physicist Albert Einstein published his first paper outlining the theory of relativity.
in calculating very large distances or very large aggregations of matter. As the quantum theory applies to the very small, so the relativity theory applies to the verylarge. Until 1887 no flaw had appeared in the rapidly developing body of classical physics. In that year, the Michelson-Morley experiment, named after the American physicistAlbert Michelson and the American chemist Edward Williams Morley, was performed. It was an attempt to determine the rate of the motion of the earth through t...
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Star (astronomy) - astronomy.
absorbing the missing colors of light. For example, the set of dark lines made by hydrogen includes a dark red line, the set of dark lines made by sodium includes a pairof dark yellow lines, and the set of dark lines made by iron includes lines of nearly every color. Each element in the gaseous outer layer of a star produces its ownparticular pattern of dark spectrum lines, depending on the temperature and pressure of the gas. Astronomers have observed spectrum lines, or spectra, for hundredsof...
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Galileo
I
INTRODUCTION
Galileo (1564-1642), Italian physicist and astronomer who, with German astronomer Johannes Kepler, initiated the scientific revolution that flowered in the work of
English physicist Sir Isaac Newton.
V WORK IN ASTRONOMY During most of his time in Padua, Galileo showed little interest in astronomy, although in 1595 he declared in a letter that he preferred the Copernican theory that Earthrevolves around the Sun to the assumptions of Aristotle and Ptolemy that planets circle a fixed Earth ( see Astronomy: The Copernican Theory ; Ptolemaic System). A Observations with the Telescope In 1609 Galileo heard that a telescope had been invented in Holland. In August of that year he constructed a t...
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Galileo.
V WORK IN ASTRONOMY During most of his time in Padua, Galileo showed little interest in astronomy, although in 1595 he declared in a letter that he preferred the Copernican theory that Earthrevolves around the Sun to the assumptions of Aristotle and Ptolemy that planets circle a fixed Earth ( see Astronomy: The Copernican Theory ; Ptolemaic System). A Observations with the Telescope In 1609 Galileo heard that a telescope had been invented in Holland. In August of that year he constructed a t...
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Earthquake.
III CAUSES Most earthquakes are caused by the sudden slip along geologic faults. The faults slip because of movement of the Earth’s tectonic plates. This concept is called theelastic rebound theory. The rocky tectonic plates move very slowly, floating on top of a weaker rocky layer. As the plates collide with each other or slide past eachother, pressure builds up within the rocky crust. Earthquakes occur when pressure within the crust increases slowly over hundreds of years and finally exceeds...