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PLANETARIUM LITERATURE
The early planetary models
The earliest planetarium began as scale models of the sky- though we might hardly recognize them as such.
The ancient Greek astronomer Eratosthenese may have been the first to build a sky model, around 250 B.C. His device, a metal sphere and surrounding rings, moved on two axes. The metal celestial sphere moved on one axes, while the rings, which represented the paths of the sun and other planetary bodies, moved on the other. The device and those like it became known as armillary spheres.
The Greek mathematician and inventor Archimedes built an impressive armillary sphere powered by water. It is said to have been so accurate that it could reproduce eclipses of the sun and moon. Another ancestor of the modern planetarium is the celestial globe. This was a sphere on which the positions of the stars and constellations were marked so they could be viewed from the outside.
One other popular model, built in 1700s, was the orrery, named after the British earl of Orrery, for whom it was built. It was notable for showing that the Earth was just one of the solar system’s children planets, all of which were mounted on the rotating arms surrounding a central sun.
Andreas Busch built the first planetarium theatre in 1657. He constructed a large globe into which twelve people could climb. The stars were fixed on inside the globe, and the planets moved along a set of internal rings. Visitors could sit and gaze at the artificial stars and planets as if sitting under a perfectly clear night sky.
Astronomers continued to team with engineers to build such globes right upto the 20th century. Dr. Wallace Atwood of the Chicago Academy of Science built the last of these globes. Fifteen feet (4.5 meters) wide and powered by electricity, it is still on display at the academy.
The modern Planetarium
The modern form of the planetarium was developed in the early 1900s by Drs Max Wolf of the Heidelberg Observatory and Walter Bauersfeld of the Carl Zeiss company in Jena, Germany. These men were the first to envision and design a planetarium projector. Their idea, as Bauersfeld described it in 1919, revolutionized our ability to recreate the cosmos: “ The great sphere shall be fixed; its inner white surface shall serve as the projection surface for many small projectors which shall be placed in the centre of the sphere. The reciprocal positions and motions of the little projectors shall be interconnected by suitable drive gears in such a manner that the little images of the heavenly bodies, thrown upon the fixed hemisphere, shall represent the stars visible to the naked eye, in position and in motion, just we are accustomed to see them in the natural clear sky”.
In August 1923, Bauersfeld demonstrated the first “Zeiss Model I” planetarium projector in a makeshift plaster dome on the roof of the Zeiss Factory. It showed in stunning detail the stars, Sun, Moon, and planets as they would normally be visible from Munich. Two months later the projector was installed in the Duetsches Museum, opening to the public on October 21, 1923. “ The wonder of Jena”, as it soon became known, captured the public’s imagination as no astronomical novelty ever had.
The Zeiss Company soon began to construct more planetarium projectors and developed the dumbbell-shaped projecting instrument. At the centre of each end of the dumbbell is a high-powered lamp. Arranged around each lamp are numerous lens systems, each containing a metal slide of an area of the sky. Tiny holes in the slides represent individual stars and constellations. As light passes through each hole, a point of light—or star – is formed on the dome ceiling. Bigger holes are needed to project bright stars. Recreating the brightest stars requires separate projectors equipped with filters to produce each star’s correct colour.
The first such planetarium in the United States was built in 1930 in Chicago. It became known as the Alder Planetarium, and was one of only half a dozen planetariums in the world.
In 1947 Armand Spitz, an amateur astronomer from Philadelphia, designed and built a smaller, simpler, and less expensive planetarium projector. His invention enabled many small museums, libraries, and schools to install their own, more economical planetariums.
Since that time, planetariums have been springing up at an average rate of 30 a year. Today there are nearly 1400 operating around the world. In addition to the Zeiss and Spitz models, some 165 different types can be found in 64 countries on six continents.
Colourful lasers, rotating planets, swirling clouds, and whizzing spacecraft fill the planetarium dome. Behind such spectacular illusions lies the hardware that forms the planetarium itself. Modern planetariums also hide elaborate special effects behind this inner dome.
In 1983 a totally new type of planetarium instrument burst onto the scene. Introduced by Evans and Sutherland Computer Corporation, the “Digistar”, a computer graphics imaging device, projects first-generation computer animation onto the planetarium dome.
In addition, some planetarium theaters are used to show motion pictures with immense film formats and gigantic, yet crisp images. Omnimax projectors, use 70 mm wide film projected across the entire dome. Smaller theaters use 35 mm projectors such as the “Cine 360” to project similar films.