Planetarium
A planetarium (pl.: planetariums or planetaria) is a theatre built primarily for presenting educational and entertaining shows about astronomy and the night sky, or for training in celestial navigation.[1][2][3]
A dominant feature of most planetariums is the large
Planetaria 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 at Liberty Science Center in New Jersey, its dome measuring 27 meters in diameter. The Birla Planetarium in Kolkata, India is the largest by seating capacity, having 630 seats.[4] In North America, the Hayden Planetarium at the American Museum of Natural History in New York City has the greatest number of seats, at 423.
The term planetarium is sometimes used generically to describe other devices which illustrate the Solar System, such as a computer simulation or an orrery. Planetarium software refers to a software application that renders a three-dimensional image of the sky onto a two-dimensional computer screen, or in a virtual reality headset for a 3D representation.[5] The term planetarian is used to describe a member of the professional staff of a planetarium.
History
This section needs additional citations for verification. (October 2022) |
Early
The ancient Greek polymath Archimedes is attributed with creating a primitive planetarium device that could predict the movements of the Sun and the Moon and the planets.[citation needed] The discovery of the Antikythera mechanism proved that such devices already existed during antiquity, though likely after Archimedes' lifetime. Campanus of Novara described a planetary equatorium in his Theorica Planetarum, and included instructions on how to build one. The Globe of Gottorf built around 1650 had constellations painted on the inside.[6] These devices would today usually be referred to as orreries (named for the Earl of Orrery). In fact, many planetariums today have projection orreries, which project onto the dome the Solar System (including the Sun and planets up to Saturn) in their regular orbital paths.
In 1229, following the conclusion of the
The small size of typical 18th century orreries limited their impact, and towards the end of that century a number of educators attempted to create a larger sized version. The efforts of Adam Walker (1730–1821) and his sons are noteworthy in their attempts to fuse theatrical illusions with education. Walker's Eidouranion was the heart of his public lectures or theatrical presentations. Walker's 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 (13 m) in diameter. These devices most probably sacrificed astronomical accuracy for crowd-pleasing spectacle and sensational and awe-provoking imagery.
The
In 1905
While this was being constructed, von Miller was also working at the Zeiss factory with German astronomer
After World War II
When Germany was divided into East and West Germany after the war, the Zeiss firm was also split. Part remained in its traditional headquarters at Jena, in East Germany, and part migrated to West Germany. The designer of the first planetariums 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 planetariums in 1954, and the East German firm started making small planetariums 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 the
A great boost to the popularity of the planetarium worldwide was provided by the Space Race of 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 planetariums in U.S. high schools.
Armand Spitz recognized that there was a viable market for small inexpensive planetaria. His first model, the Spitz A, was designed to project stars from a dodecahedron, thus reducing machining expenses in creating a globe.[11] 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.
Phillip Stern, as former lecturer at
During the 1970s, the
When Germany reunified in 1989, the two Zeiss firms did likewise, and expanded their offerings to cover many different size domes.
Computerized planetaria
In 1983,
Technology
Domes
-
The dome of the Vilnius University Planetarium.
-
The dome of the Athens Planetarium.
-
The Large Zeiss Planetarium in Berlin, 1987.
-
Dome of the Planetarium Science Center of the Bibliotheca Alexandrina
-
A small inflatable portable planetarium dome.
-
GM-II starfield projector atTrivandrum, India
-
Trivandrum, India
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.[13] 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 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.
Planetaria 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.
Traditionally, planetariums needed many
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.
Some new planetariums now feature a glass floor, which allows spectators to stand near the center of a sphere surrounded by projected images in all directions, giving the impression of floating in outer space. For example, a small planetarium at AHHAA in Tartu, Estonia features such an installation, with special projectors for images below the feet of the audience, as well as above their heads.[14]
Traditional electromechanical/optical projectors
Traditional planetarium projection apparatus use 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
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:-
- 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.)
- 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
- 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.
Digital projectors
An increasing number of planetariums are using digital technology 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 planetariums mix both traditional opto-mechanical projection and digital technologies on the same dome.
In a fully digital planetarium, the dome image is generated by a
Digital projection systems all work by creating the image of the night sky as a large array of
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.
Show content
Worldwide, most planetariums provide shows to the general public. Traditionally, shows for these audiences with themes such as "What's in the sky tonight?", or shows which pick up on topical issues such as a religious festival (often the Christmas star) linked to the night sky, have been popular. Live format is preferred by many venues as a live speaker or presenter can answer questions raised by the audience.[citation needed]
Since the early 1990s, fully featured
See also
References
- ^ King, Henry C. "Geared to the Stars; the evolution of planetariums, orreries, and astronomical clocks" University of Toronto Press, 1978
- ^ Directory of Planetariums, 2005, International Planetarium Society
- ^ Catalog of New York Planetariums, 1982
- ^ "Birla Planetarium ready to welcome visitors after 28-month break - Times of India". The Times of India. 18 July 2017. Retrieved 2019-04-10.
- ^ "PlanetariumVR".
- ISBN 9780813537665. Archived from the originalon 2016-03-04. Retrieved 2014-02-24.
- ^ "History of Planetariums". commons.bcit.ca. Retrieved 2022-10-27.
- ^ Centre, UNESCO World Heritage. "Eise Eisinga Planetarium". UNESCO World Heritage Centre. Retrieved 2022-10-27.
- ^ Engber, Daniel (24 February 2014). "Under the Dome: The tragic, untold story of the world's first planetarium". Slate. The Slate Group. Archived from the original on 24 February 2014. Retrieved 24 February 2014.
- ISSN 0090-3213. Archived from the originalon 2009-04-20. Retrieved 2009-02-26.
- ^ Ley, Willy (February 1965). "Forerunners of the Planetarium". For Your Information. Galaxy Science Fiction. pp. 87–98.
- ^ "- Bhasani Novo Theatre". www.mosict.gov.bd. Archived from the original on 27 March 2009. Retrieved 6 June 2022.
- ^ "ESOblog: How to Install a Planetarium A conversation with engineer Max Rößner about his work on the ESO Supernova". www.eso.org. Archived from the original on 7 May 2018. Retrieved 21 February 2018.
- ^ Aru, Margus (March–June 2012). "Under One Dome: AHHAA Science Centre Planetarium" (PDF). Planetarian: Journal of the International Planetarium Society. 41 (2): 37. Archived (PDF) from the original on 2015-10-02. Retrieved 2017-06-02.