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This article is about the theatre for observing the night sky. For other uses, seePlanetarium (disambiguation).

Inside a planetarium projection hall.

Inside the same hall during projection.

A planetarium under construction inNishapur, near theMausoleum of Omar Khayyam.

Aplanetarium(pluralplanetariaorplanetariums) is atheatrebuilt primarily for presenting educational and entertaining shows aboutastronomyand the night sky, or for training incelestial navigation.[1][2][3]

A dominant feature of most planetaria is the largedome-shaped projection screen onto which scenes ofstarsplanetsand othercelestial objectscan be made to appear and move realistically to simulate the complex motions of the heavens. The celestial scenes can be created using a wide variety of technologies, for example precision-engineered star balls that combine optical and electro-mechanical technology,slide projectorvideoandfulldomeprojector systems, and lasers. Whatever technologies are used, the objective is normally to link them together to provide an accurate relative motion of the sky. Typical systems can be set to display the sky at any point in time, past or present, and often to show the night sky as it would appear from any point oflatitudeon Earth.

Planetariums range in size from the 37 meter dome in St. Petersburg, Russia (called Planetarium No 1) to three-meter inflatable portable domes where attendees sit on the floor. The largest planetarium in the Western Hemisphere is the Jennifer Chalsty Planetarium atLiberty Science CenterinNew Jersey(27 meters in diameter). The China Science and Technology Museum Planetarium inBeijingChinahas the largest seating capacity worldwide (442 seats). In North America, the Hayden Planetarium at theAmerican Museum of Natural HistoryinNew York Cityhas the greatest number of seats (423).

The termplanetariumis sometimes used generically to describe other devices which illustrate the solar system, such as a computer simulation or anorrery.Planetarium softwarerefers to a software application that renders a three-dimensional image of the sky onto a two-dimensional computer screen. The termplanetarianis used to describe a member of the professional staff of a planetarium.

For specific dates and events in the historical influences on and development of planetaria, seetimeline of planetariums.

The Mark I projector installed in the Deutsches Museum in 1923 was the worlds first planetarium projector.

Theis attributed with creating a primitive planetarium device that could predict the movements of theSunand theMoonand the planets. The discovery of theAntikythera mechanismproved that such devices already existed duringantiquity, though likely after Archimedes lifetime.Campanus of Novara(12201296) described a planetaryequatoriumin hisTheorica Planetarum, and included instructions on how to build one. TheGlobe of Gottorfbuilt around 1650 had constellations painted on the inside.[4]These devices would today usually be referred to asorreries(named for theEarl of Orrery, an Irish peer: an 18th-century Earl of Orrery had one built). In fact, many planetaria today have what are called projection orreries, which project onto the dome a Sun with planets (usually limited to Mercury up to Saturn) going around it in something close to their correct relative periods.

The small size of typical 18th century orreries limited their impact, and towards the end of that century a number of educators attempted some larger scale simulations of the heavens. The efforts ofAdam Walker(17301821) and his sons are noteworthy in their attempts to fuse theatrical illusions with educational aspirations. WalkersEidouranionwas the heart of his public lectures or theatrical presentations. Walkers son describes this Elaborate Machine as twenty feet high, and twenty-seven in diameter: it stands vertically before the spectators, and its globes are so large, that they are distinctly seen in the most distant parts of the Theatre. Every Planet and Satellite seems suspended in space, without any support; performing their annual and diurnal revolutions without any apparent cause. Other lecturers promoted their own devices: R E Lloyd advertised his Dioastrodoxon, or Grand Transparent Orrery, and by 1825 William Kitchener was offering his Ouranologia, which was 42 feet (13m) in diameter. These devices most probably sacrificed astronomical accuracy for crowd-pleasing spectacle and sensational and awe-provoking imagery.

Theoldest, still working planetariumcan be found in the Dutch townFraneker. It was built byEise Eisinga(17441828) in the living room of his house. It took Eisinga seven years to build his planetarium, which was completed in 1781.

In 1905Oskar von Miller(18551934) of theDeutsches MuseuminMunichcommissioned updated versions of a geared orrery and planetarium from M Sendtner, and later worked with Franz Meyer, chief engineer at the CarlZeissoptical works inJena, on the largest mechanical planetarium ever constructed, capable of displaying bothheliocentricandgeocentricmotion. This was displayed at the Deutsches Museum in 1924, construction work having been interrupted by the war. The planets travelled along overhead rails, powered by electric motors: the orbit of Saturn was 11.25 m in diameter. 180 stars were projected onto the wall by electric bulbs.

While this was being constructed, von Miller was also working at the Zeiss factory with German astronomerMax Wolf, director of theLandessternwarte Heidelberg-Königstuhlobservatory of theUniversity of Heidelberg, on a new and novel design, inspired byWallace W. Atwoods work at theChicago Academy of Sciencesand by the ideas ofWalther Bauersfeldand Rudolf Straubel[5]atZeiss. The result was a planetarium design which would generate all the necessary movements of the stars and planets inside the optical projector, and would be mounted centrally in a room, projecting images onto the white surface of a hemisphere. In August 1923, the first (Model I) Zeiss planetarium projected images of the night sky onto the white plaster lining of a 16 m hemispherical concrete dome, erected on the roof of the Zeiss works. The first official public showing was at the Deutsches Museum in Munich on October 21, 1923.[6]

When Germany was divided into East and West Germany after the war, the Zeiss firm was also split. Part remained in its traditional headquarters atJena, inEast Germany, and part migrated toWest Germany. The designer of the first planetaria for Zeiss,Walther Bauersfeld, also migrated to West Germany with the other members of the Zeiss management team. There he remained on the Zeiss West management team until his death in 1959.

The West German firm resumed making large planetaria in 1954, and the East German firm started making small planetaria a few years later. Meanwhile, the lack of planetarium manufacturers had led to several attempts at construction of unique models, such as one built by theCalifornia Academy of SciencesinGolden Gate ParkSan Francisco, which operated 1952-2003. The Korkosz brothers built a large projector for theBoston Museum of Science, which was unique in being the first (and for a very long time only) planetarium to project the planetUranus. Most planetaria ignore Uranus as being at best marginally visible to the naked eye.

A great boost to the popularity of the planetarium worldwide was provided by theSpace Raceof the 1950s and 60s when fears that the United States might miss out on the opportunities of the new frontier in space stimulated a massive program to install over 1,200 planetaria in U.S. high schools.

Armand Spitzrecognized that there was a viable market for small inexpensive planetaria. His first model, the Spitz A, was designed to project stars from adodecahedron, thus reducing machining expenses in creating a globe.[7]Planets were not mechanized, but could be shifted by hand. Several models followed with various upgraded capabilities, until the A3P, which projected well over a thousand stars, had motorized motions for latitude change, daily motion, and annual motion for Sun, Moon (including phases), and planets. This model was installed in hundreds of high schools, colleges, and even small museums from 1964 to the 1980s.

Japanentered the planetarium manufacturing business in the 1960s, with Goto andMinoltaboth successfully marketing a number of different models. Goto was particularly successful when the Japanese Ministry of Education put one of their smallest models, the E-3 or E-5 (the numbers refer to the metric diameter of the dome) in everyelementary schoolin Japan.

Phillip Stern, as former lecturer atNew York CityHayden Planetarium, had the idea of creating a small planetarium which could be programmed. His Apollo model was introduced in 1967 with a plastic program board, recorded lecture, and film strip. Unable to pay for this himself, Stern became the head of the planetarium division ofViewlex, a mid-size audio-visual firm onLong Island. About thirty canned programs were created for various grade levels and the public, while operators could create their own or run the planetarium live. Purchasers of the Apollo were given their choice of two canned shows, and could purchase more. A few hundred were sold, but in the late 1970s Viewlex went bankrupt for reasons unrelated to the planetarium business.

During the 1970s, thesystem (now known as IMAX Dome) was conceived to operate on planetarium screens. More recently, some planetaria have re-branded themselves asdome theaters, with broader offerings including wide-screen or wraparound films,fulldome video, and laser shows that combine music with laser-drawn patterns.

Learning Technologies Massachusettsoffered the first easily portable planetarium in 1977. Philip Sadler designed this patented system which projected stars,constellationfigures from manymythologies, celestial coordinate systems, and much else, from removable cylinders (Viewlex and others followed with their own portable versions).

WhenGermany reunifiedin 1989, the two Zeiss firms did likewise, and expanded their offerings to cover many different size domes.

Bangabandhu Sheikh Mujibur Rahman Planetarium(Est.2003),DhakaBangladeshuses Astrotec perforated aluminum curtain, GSS-Helios Space Simulator, Astrovision-70 and many other special effects projectors

In 1983,Evans & Sutherlandinstalled the first planetarium projector displaying computer graphics (Hansen Planetarium, Salt Lake City, Utah)the Digistar I projector used avector graphics systemto display starfields as well asline art.

The newest generation of planetaria offer a fullydigitalprojection system, usingfulldome videotechnology. This gives the operator great flexibility in showing not only the modern night sky as visible fromEarth, 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 planetaria was released in Japan byTakayuki Ohirain cooperation withSega. Ohira is worldwide known as a mastermind for building portable planetaria used at exhibitions and events such as the Aichi World Expo in 2005. Later, theMegastarstar 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.[9]

In 2009Microsoft ResearchandGo-Domepartnered on theWorldWide Telescopeproject. The goal of the project is to bring sub-$1000 planetaria to small groups of school children as well as provide technology for large public planetaria.

The Large Zeiss Planetarium in Berlin, 1987.

Inside of the Planetarium located in theScience Factory (Vitenfabrikken)inSandnesNorway.

Dome of thePlanetarium Science Centerof theBibliotheca Alexandrina

A small inflatable portable planetarium dome.

GM-II starfield projector atPriyadarshini PlanetariumTrivandrumIndia

Priyadarshini PlanetariumTrivandrumIndia

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

Portableinflatabledomes can be inflated in minutes. Such domes are often used for touring planetaria visiting, for example, schools and community centres.

Temporary structures usingglass-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, allowingatmospheric pressureto 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, theacousticsinside 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 withplaster. This method is relatively expensive and suffers the sameacousticandventilationissues as GRP.

Most modern domes are built from thinaluminiumsections 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.

The realism of the viewing experience in a planetarium depends significantly on thedynamic rangeof 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 theblack levelthere 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.

Planetaria occasionally include controls such as buttons orjoysticksin the arm-rests of seats to allow audience feedback that influences the show inreal time.

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

Silhouettemodels of geography or buildings like those in the area round the planetarium building.

Lighting to simulate the effect of twilight or urbanlight pollution.

In one planetarium the horizon decor included a small model of aUFOflying.

Traditionally, planetaria needed manyincandescent lampsaround the cove of the dome to help audience entry and exit, to simulatesunriseandsunset, and to provide working light for dome cleaning. More recently, solid-stateLEDlighting 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 worlds largest mechanical planetarium is located in Monico, Wisconsin. TheKovac 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 theAtwood Globein Chicago (15 feet in diameter) and one third the size of the Hayden.

Some new planetariums now feature aglass floor, which allows spectators to stand near the center of aspheresurrounded by projected images in all directions, giving the impression of floating inouter space. For example, a small planetarium atAHHAAinTartuEstoniafeatures such an installation, with special projectors for images below the feet of the audience, as well as above their heads.[11]

Traditional electromechanical/optical projectors

It has been suggested that portions of this section besplitout into another article titled

AZeiss projectorin a Berlin planetarium during a show in 1939.

Zeiss projector atMontreal Planetarium

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

Traditionalplanetarium projection apparatususes 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.SiriusCanopusVega), 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 Earths daily rotation, and to change the simulated latitude on Earth. There is also usually a means of rotating to produce the effect ofprecession of the equinoxes. Often, one such ball is attached at its southeclipticpole. 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 adumbbell. 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 variousnebulae. Larger projectors also includecometsand 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 theMilky Way. Others add coordinate lines andconstellations, photographic slides,laserdisplays, and other images.

Each planet is projected by a sharply focusedspotlightthat 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:-

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 throughmetal fatigue.

When a planet is atoppositionto the Earth, its light is liable to be blocked by the mechanisms 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 atconjunctionwith 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 Ptolemys 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 forUranus, 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 acomputer.

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 todark adaptits 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 properoccultation. 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 planetaria 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.

An increasing number of planetaria are usingdigitaltechnology to replace the entire system of interlinked projectors traditionally employed around a star ball to address some of their limitations. Digital planetarium manufacturers claim reduced maintenance costs and increased reliability from such systems compared with traditional star balls on the grounds that they employ few moving parts and do not generally require synchronisation of movement across the dome between several separate systems. Some planetaria mix both traditional opto-mechanical projection and digital technologies on the same dome.

In a fully digital planetarium, the dome image is generated by acomputerand then projected onto the dome using a variety of technologies includingcathode ray tubeLCDDLPorlaserprojectors. Sometimes a single projector mounted near the centre of the dome is employed with afisheye lensto spread the light over the whole dome surface, while in other configurations several projectors around the horizon of the dome are arranged to blend together seamlessly.

Digital projection systems all work by creating the image of the night sky as a large array ofpixels. Generally speaking, the more pixels a system can display, the better the viewing experience. While the first generation of digital projectors were unable to generate enough pixels to match the image quality of the best traditional star ball projectors, high-end systems now offer a resolution that approaches the limit of humanvisual acuity.

LCD projectors have fundamental limits on their ability to project true black as well as light, which has tended to limit their use in planetaria.LCOSand modified LCOS projectors have improved on LCDcontrast ratioswhile also eliminating the screen door effect of small gaps between LCD pixels. Dark chip DLP projectors improve on the standard DLP design and can offer relatively inexpensive solution with bright images, but the black level requires physical baffling of the projectors. As the technology matures and reduces in price, laser projection looks promising for dome projection as it offers bright images, large dynamic range and a very widecolor space.

Worldwide, most planetaria provide shows to the general public. Traditionally, shows for these audiences with themes such as Whats in the sky tonight?, or shows which pick up on topical issues such as a religious festival (often theChristmas star) linked to the night sky, have been popular. Pre-recorded and live presentation formats are possible. Live format are preferred by many venues because a live expert presenter can answer on-the-spot questions raised by the audience.

Since the early 1990s, fully featured3-Ddigital planetaria have added an extra degree of freedom to a presenter giving a show because they allow simulation of the view from any point in space, not only the earth-bound view which we are most familiar with. This newvirtual realitycapability to travel through the universe provides importanteducationalbenefits because it vividly conveys that space has depth, helping audiences to leave behind the ancient misconception that the stars are stuck on the inside of a giantcelestial sphereand instead to understand the true layout of thesolar systemand beyond. For example, a planetarium can now fly the audience towards one of the familiar constellations such asOrion, revealing that the stars which appear to make up a co-ordinated shape from our earth-bound viewpoint are at vastly different distances from Earth and so not connected, except in human imagination andmythology. For especially visual orspatially awarepeople, this experience can be more educationally beneficial than other demonstrations.

Music is an important element to fill out the experience of a good planetarium show, often featuring forms ofspace-themed music, or music from the genres ofspace musicspace rock, orclassical music.

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