A globe is a two-dimensional scale model of a spheroid celestial body such as a planet, star or moon, in particular Earth, or, alternatively, a spherical representation of the sky with the stars (but without the Sun, Moon, or planets, because their positions vary relative to those of the stars; however, the ecliptic, along which the Sun moves, is indicated).
Terrestrial globes are the only geographical representation of Earth that have negligible distortion. Spheres such as the Earth are mapped onto a flat surface using a map projection with an inherent degree of distortion. These projections can either enforce angle preservation or area preservation. A typical scale for a globe is roughly 1:40 million.
The Earth is the most popular planet represented, but globes of the Sun, the Moon and other celestial objects have been made, including fictional ones.
The earliest globe, called the "Nürnberg Terrestrial Globe", was made during the years 1490-1492 by German mapmaker Martin Behaim.
A globe is usually mounted at an angle on bearings. In addition to making it easy to use this mounting also represents the angle of the planet in relation to its sun and the spin of the planet. This makes it easy to visualize how days and seasons change.
Sometimes a globe has relief, showing topography; in the case of a globe of the Earth the elevations are exaggerated, otherwise they would be hardly visible. Most modern globes are also imprinted with parallels and meridians so that one could (if only approximately due to scale) tell where a specific point on the surface of the planet is located.
Mass-produced globes are typically covered by a printed paper map. The most common type has long, thin strips of paper that touch at the equator, and narrow to a point at the north pole and the south pole. Then a small disk is used to paper over the inevitable irregularities at the poles. The more strips there are, the less stretching and crumpling is required to make the paper map fit the sphere. From a geometric point of view, all points on a sphere are equivalent -- one could select any arbitrary point on the Earth, and create a paper map that covers the Earth with strips that come together at that point and the antipodal point. However, as the Earth is an oblate spheroid and not a perfect sphere, bulging slightly at the equator, to correctly represent the true shape of the Earth using such paper strips is more difficult.
Notable large globes:
Eartha, currently the world's largest rotating globe (41 feet in diameter), at the Delorme headquarters in Yarmouth, Maine
The Mapparium, 30 foot walk-in globe at the Christian Science complex in Boston, intended to be viewed from within.
The Babson globe in Wellesley, Massachusetts, a 26-foot diameter globe which originally rotated on its axis and on its base to simulate day and night and the seasons
The giant globe in the lobby of The News Building in New York City.
Earth Globe
OUR PLANET...
The most accurate world map is a globe. Like the planet Earth, a globe is shaped as a ball. When you look at a globe you can truly see the way the world looks in all of its complexity. All the countries are shown in true size relative to each other. You can see how far apart different cities are, and you can learn what time it is in another part of the world.
Why are globes so much more accurate than flat maps of the world? If you peeled the paper off a globe and tried to lay it out on a table like a map, you'd have a hard time. The map would have all sorts of gaps in it. But that's essentially what cartographers have been trying to do for hundreds of years. On some flat maps, pieces of land near the North Pole look larger than they are in reality. For example, Antarctica stretches across the bottom of a flat map when it is really a circular continent. Of course, flat maps can be very useful; you cannot put a globe in your pocket while you are traveling. But if you want to "think globally," it is obvious that a globe is what you need.
FLAT-OUT WRONG...
When astronauts look down at the earth from outer space, it looks like a huge blue and white marble. But thousands of years ago, before rocket boosters and space shuttles were invented; it was impossible to see what the world looked like from above. Ancient people had no way of flying so they could only look around and try to imagine the shape of their world.
In most places, the ground they were standing on was more or less flat, so they guessed the whole world must be flat. If you went all the way to the edge of the world, they thought, you would fall off or be swallowed by monsters.
In Greece, storytellers used to describe the world as a flat disk, surrounded by the "Ocean River." Hundreds of years later, Aztec Indians in Central America had a very similar idea: They believed the world was a flat disk with a great circle of water around it.
A WELL-ROUNDED IDEA...
Even thousands of years ago, people saw things happening around them everyday that couldn't be explained by the theory of a flat world. If the world was flat, why did the sun always come up every morning in the east and go down every evening in the west? And why did the stars move in a circle in the night sky? These movements in the sky didn't prove that the world wasn't flat. But they gave clues about the real shape of the earth.
At first, ancient peoples came up with myths to explain these mysteries. Some of them said a chariot pulled the sun across the sky each day. But not everyone believed these stories. Little by little, more people in the ancient world came to believe that the world was a sphere.
A SHADOW OF THE TRUTH...
Around 250 BC, the Greek mathematician Eratosthenes noticed that a post in the city of Alexandria, Egypt cast a shadow at noon on the summer solstice, the longest day of the year. But at the same time in Syrene, a town due south from Alexandria, a similar post did not cast any shadow. Why was this?
Eratosthenes figured the sun must be shining its light at these two towns from different angles. The sun was directly above the post in Syrene, so the post did not cast any shadow. But the sunlight was shining toward Alexandria at an angle. This was because the earth's surface was curved, Eratosthenes reasoned.
By knowing the distance between the two cities and by calculating the angle of the pole to the shadow, Eratosthenes was able to apply geometric theory to determine the size of the earth. He figured out the diameter of the earth was 7,850 miles (12,633 kilometers). He was only off a little. The earth's actual diameter is about 7,926 miles (12,757 kilometers) at the equator.
THE CENTER OF THE UNIVERSE?...
By then, many Greeks knew for sure the world was shaped like a globe. However, most of them didn't have any idea how this globe fit into the rest of the universe. Aristarchus, who lived in the 200s BC, said the earth revolved around the sun, but not many people believed him. Instead, they believed Claudius Ptolemy, an astronomer who said in 150 BC that the earth was at the center of the universe. Ptolemy said the moon, the sun, the planets and stars revolved around the earth in a series of circles. For another 1,400 years, many people mistakenly believed that this was a true picture of the universe.
In 140 BC, a Greek known as Crates of Mallus built what may have been the first globe in history. It is hard to picture what was on that globe, since the Greeks only knew what a small part of the planet looked like. They had never traveled to China, Australia or the Americas, so none of those places could have been on the globe.
A VERY BIG EGG...
Thousands of miles away, around the same time, some Chinese astronomers thought the earth was a hemisphere-like globe sliced in half underneath a dome-shaped universe. Other Chinese thinkers believed the universe was shaped like an egg, with a sphere-shaped earth in the middle of the egg. In other words, they thought of the earth as the yolk.
And then there was a third group of Chinese astronomers who said the universe was an infinitely large, almost empty space, where spheres like the sun, the moon and the earth just floated around, very far away from each other. This was very close to the truth known by scientists today. But as the Greeks, the Chinese dropped this idea and stuck with the theory of the egg-shaped universe.
ARABIAN NIGHT-WATCHERS...
Astronomers in India learned about the universe by reading books written by the Greeks. Around 500 AD, an Indian astronomer Aryabhata explained why the stars circled the earth in the night sky. He believed the earth must be spinning like a top.
The Arabs learned about astronomy from these previous cultures, and they became some of the best astronomers of the Middle Ages. Like the Greeks before them, the Arabs used sun shadows to measure how big around the world was. In the 1300s, a former slave in Arabia named al-Khazini came up with a theory of gravity. He said all objects were attracted to the center of the earth.
DEBUNKING OLD MYTHS...
Before European explorers and conquerors sailed across the oceans in the 1400s and 1500s, cartographers in Europe made globes. In 1492, Martin Behaim, a German cartographer, made the oldest globe that still exists today. Years later, the Dutch would become famous for making the best globes and maps.
When the kings and queens of Europe gazed upon these wonderful spherical maps, they still imagined the rest of the universe circling around the earth. But in the 1500s and 1600s, Polish astronomer Nicolaus Copernicus, German astronomer Johannes Kepler and Italian astronomer Galileo Galilei debunked the myth that the earth was at the center of everything. They showed that the earth was actually a planet moving around the sun. Many religious leaders refused to believe these new ideas, threatening Galileo and banning the books of Copernicus.
Sir lsaac Newton, came up with the first theory that explained the movements of the stars, the sun, the moon and the planets. Newton realized the force that causes an apple to fall from a tree to the ground is the same force that attracts the moon to the earth. Newton explained how this force called gravity holds the solar system together. Today, scientists are still getting more information about the universe and the laws of physics, but the rules discovered by Newton still give a good, basic description of the universe around us.
Reprinted from: "A guide to Your Globe" by Replogle Globes Inc.
A sphere (Greek: óöáῖñá) is a perfectly symmetrical, three-dimensional geometrical object. In mathematics, the term refers to the surface or boundary of a ball, but in non-mathematical usage, the term is used to refer either to a three-dimensional ball or to its surface. This article deals with the mathematical concept of a sphere. In physics, a sphere is an object (usually idealized for the sake of simplicity) capable of colliding or stacking with other objects which occupy space.
In three-dimensional Euclidean geometry, a sphere is the set of points in R3 which are at distance r from a fixed point of that space, where r is a positive real number called the radius of the sphere. The fixed point is called the center or centre, and is not part of the sphere itself. The special case of r = 1 is called a unit sphere.
|
