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Planetariums

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Majir
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« Reply #15 on: April 25, 2011, 04:32:52 pm »

Computerized planetariums

In 1983, Evans & Sutherland installed the first planetarium projector displaying computer graphics (Hansen Planetarium, Salt Lake City, Utah)—the Digistar I projector used a vector graphics system to display starfields as well as line art.

The newest generation of planetariums offer a fully digital projection system, using fulldome video technology. This gives the operator great flexibility in showing not only the modern night sky as visible from Earth, but any other image they wish (including the night sky as visible from points far distant in space and time).

A new generation of home planetariums was released in Japan by Takayuki Ohira in cooperation with Sega. Ohira is worldwide known as a mastermind for building portable planetariums used at exhibitions and events such as the Aichi World Expo in 2005. Later, the Megastar star projectors released by Takayuki Ohira were installed in several science museums around the world. Meanwhile, Sega Toys continues to produce the Homestar series intended for home use, however by projecting 10,000 stars on the ceiling makes it semi-professional.[2]

In 2009 Microsoft Research and Go-Dome partnered on the WorldWide Telescope project. The goal of the project is to bring sub-$1000 planetariums to small groups of school children as well as provide technology for large public planetariums.

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« Reply #16 on: April 25, 2011, 04:33:35 pm »



Bangabandhu Sheikh Mujibur Rahman Planetarium(Est.2003), Dhaka, Bangladesh uses Astrotec perforated aluminum curtain, GSS-Helios Space Simulator, Astrovision-70 and many other special effects projectors [1]
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« Reply #17 on: April 25, 2011, 04:35:22 pm »

Planetarium technology

Domes

Planetarium domes range in size from 3 to 35 m in diameter, accommodating from 1 to 500 people. They can be permanent or portable, depending on the application.

Portable inflatable domes can be inflated in minutes. Such domes are often used for touring planetariums visiting, for example, schools and community centres.
Temporary structures using Glass-reinforced plastic (GRP) segments bolted together and mounted on a frame are possible. As they may take some hours to construct, they are more suitable for applications such as exhibition stands, where a dome will stay up for a period of at least several days.
Negative-pressure inflated domes are suitable in some semi-permanent situations. They use a fan to extract air from behind the dome surface, allowing atmospheric pressure to push it into the correct shape.
Smaller permanent domes are frequently constructed from glass reinforced plastic. This is inexpensive but, as the projection surface reflects sound as well as light, the acoustics inside this type of dome can detract from its utility. Such a solid dome also presents issues connected with heating and ventilation in a large-audience planetarium, as air cannot pass through it.
Older planetarium domes were built using traditional construction materials and surfaced with plaster. This method is relatively expensive and suffers the same acoustic and ventilation issues as GRP.
Most modern domes are built from thin aluminium sections with ribs providing a supporting structure behind. The use of aluminium makes it easy to perforate the dome with thousands of tiny holes. This reduces the reflectivity of sound back to the audience (providing better acoustic characteristics), lets a sound system project through the dome from behind (offering sound that seems to come from appropriate directions related to a show), and allows air circulation through the projection surface for climate control.
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« Reply #18 on: April 25, 2011, 04:35:39 pm »

The realism of the viewing experience in a planetarium depends significantly on the dynamic range of the image, i.e., the contrast between dark and light. This can be a challenge in any domed projection environment, because a bright image projected on one side of the dome will tend to reflect light across to the opposite side, "lifting" the black level there and so making the whole image look less realistic. Since traditional planetarium shows consisted mainly of small points of light (i.e., stars) on a black background, this was not a significant issue, but it became an issue as digital projection systems started to fill large portions of the dome with bright objects (e.g., large images of the sun in context). For this reason, modern planetarium domes are often not painted white but rather a mid grey colour, reducing reflection to perhaps 35-50%. This increases the perceived level of contrast.

A major challenge in dome construction is to make seams as invisible as possible. Painting a dome after installation is a major task and, if done properly, the seams can be made almost to disappear.

Traditionally, planetarium domes were mounted horizontally, matching the natural horizon of the real night sky. However, because that configuration requires highly inclined chairs for comfortable viewing "straight up", increasingly domes are being built tilted from the horizontal by between 5 and 30 degrees to provide greater comfort. Tilted domes tend to create a favoured 'sweet spot' for optimum viewing, centrally about a third of the way up the dome from the lowest point. Tilted domes generally have seating arranged 'stadium-style' in straight, tiered rows; horizontal domes usually have seats in circular rows, arranged in concentric (facing center) or epicentric (facing front) arrays.

Planetariums occasionally include controls such as buttons or joysticks in the arm-rests of seats to allow audience feedback that influences the show in real time.

Often around the edge of the dome (the 'cove') are:

Silhouette models of geography or buildings like those in the area round the planetarium building.
Lighting to simulate the effect of twilight or urban light pollution.
In one planetarium the horizon decor included a small model of a UFO flying.
Traditionally, planetariums needed many incandescent lamps around the cove of the dome to help audience entry and exit, to simulate sunrise and sunset, and to provide working light for dome cleaning. More recently, solid-state LED lighting has become available that significantly decreases power consumption and reduces the maintenance requirement as lamps no longer have to be changed on a regular basis.

The world's largest mechanical planetarium is located in Monico, Wisconsin. The Kovac Planetarium. It is 22 feet in diameter and weighs two tons. The globe is made of wood and is driven with a variable speed motor controller. This is the largest mechanical planetarium in the world, larger than the Atwood Globe in Chicago (15 feet in diameter) and one third the size of the Hayden.

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« Reply #19 on: April 25, 2011, 04:36:27 pm »



The dome of the Athens Planetarium.
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« Reply #20 on: April 25, 2011, 04:37:03 pm »



The Hamburg planetarium
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« Reply #21 on: April 25, 2011, 04:37:58 pm »



The Large Zeiss Planetarium in Berlin, 1987.
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« Reply #22 on: April 25, 2011, 04:38:39 pm »



Dome of the Planetarium Science Center of the Bibliotheca Alexandrina
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« Reply #23 on: April 25, 2011, 04:39:22 pm »



A small inflatable portable planetarium dome.
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« Reply #24 on: April 25, 2011, 04:39:51 pm »

http://en.wikipedia.org/wiki/Planetarium
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« Reply #25 on: April 25, 2011, 04:40:12 pm »

Traditional electromechanical/optical projectors

Traditional planetarium projection apparatus uses a hollow ball with a light inside, and a pinhole for each star, hence the name "star ball". With some of the brightest stars (e.g. Sirius, Canopus, Vega), the hole must be so big to let enough light through that there must be a small lens in the hole to focus the light to a sharp point on the dome. In later and modern planetarium star balls, the individual bright stars often have individual projectors, shaped like small hand-held torches, with focusing lenses for individual bright stars. Contact breakers prevent the projectors from projecting below the 'horizon'.[citation needed]

The star ball is usually mounted so it can rotate as a whole to simulate the Earth's daily rotation, and to change the simulated latitude on Earth. There is also usually a means of rotating to produce the effect of precession of the equinoxes. Often, one such ball is attached at its south ecliptic pole. In that case, the view cannot go so far south that any of the resulting blank area at the south is projected on the dome. Some star projectors have two balls at opposite ends of the projector like a dumbbell. In that case all stars can be shown and the view can go to either pole or anywhere between. But care must be taken that the projection fields of the two balls match where they meet or overlap.

Smaller planetarium projectors include a set of fixed stars, Sun, Moon, and planets, and various nebulae. Larger projectors also include comets and a far greater selection of stars. Additional projectors can be added to show twilight around the outside of the screen (complete with city or country scenes) as well as the Milky Way. Others add coordinate lines and constellations, photographic slides, laser displays, and other images.

Each planet is projected by a sharply focused spotlight that makes a spot of light on the dome. Planet projectors must have gearing to move their positioning and thereby simulate the planets' movements. These can be of these types:-

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« Reply #26 on: April 25, 2011, 04:40:36 pm »



Copernican. The axis represents the Sun. The rotating piece that represents each planet carries a light that must be arranged and guided to swivel so it always faces towards the rotating piece that represents the Earth. This presents mechanical problems including:
The planet lights must be powered by wires, which have to bend about as the planets rotate, and repeatedly bending copper wire tends to cause wire breakage through metal fatigue.
When a planet is at opposition to the Earth, its light is liable to be blocked by the mechanism's central axle. (If the planet mechanism is set 180° rotated from reality, the lights are carried by the Earth and shine towards each planet, and the blocking risk happens at conjunction with Earth.)
Ptolemaic. Here the central axis represents the Earth. Each planet light is on a mount which rotates only about the central axis, and is aimed by a guide which is steered by a deferent and an epicycle (or whatever the planetarium maker calls them). Here Ptolemy's number values must be revised to remove the daily rotation, which in a planetarium is catered for otherwise. (In one planetarium, this needed Ptolemaic-type orbital constants for Uranus, which was unknown to Ptolemy.)
Computer-controlled. Here all the planet lights are on mounts which rotate only about the central axis, and are aimed by a computer.
Despite offering a good viewer experience, traditional star ball projectors suffer several inherent limitations. From a practical point of view, the low light levels require several minutes for the audience to "dark adapt" its eyesight. "Star ball" projection is limited in education terms by its inability to move beyond an earth-bound view of the night sky. Finally, in most traditional projectors the various overlaid projection systems are incapable of proper occultation. This means that a planet image projected on top of a star field (for example) will still show the stars shining through the planet image, degrading the quality of the viewing experience. For related reasons, some planetariums show stars below the horizon projecting on the walls below the dome or on the floor, or (with a bright star or a planet) shining in the eyes of someone in the audience.

However, the new breed of Optical-Mechanical projectors using fiber-optic technology to display the stars, show a much more realistic view of the sky, and are far superior to any digital star projector.

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« Reply #27 on: April 25, 2011, 04:41:11 pm »



A Zeiss projector in a Berlin planetarium during a show in 1939.
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Majir
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« Reply #28 on: April 25, 2011, 04:41:49 pm »



Zeiss projector at Montreal Planetarium
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« Reply #29 on: April 25, 2011, 04:42:27 pm »



A modern, egg-shaped Zeiss projector (UNIVERSARIUM Mark IX) at the Hamburg planetarium
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