Editing Planetarium (section)

=== Domes ===
<gallery mode= "packed" class="center" caption="Examples of planetarium domes">
Bundesarchiv Bild 183-1987-1008-020, Berlin, Zeiss-Großplanetarium.jpg|The Large Zeiss Planetarium in Berlin, 1987.
EugenFound-023.jpg|The dome of the [[Athens]] Planetarium.
Hamburg Planetarium.jpg|The [[Hamburg Planetarium]]
VU planetariumas by Augustas Didzgalvis.jpg|The dome of the [[Vilnius University]] Planetarium.
Planetariet.jpg|Inside of the Planetarium located in the [[Science Factory (Vitenfabrikken)]] in [[Sandnes]], [[Norway]].
Aleksandria raamatukogu IMG 0119.JPG|Dome of the [[Planetarium Science Center]] of the [[Bibliotheca Alexandrina]]
Planetobus - kopuła mobilnego planetarium Centrum Nauki Kopernik w Warszawie.jpg|A small inflatable portable planetarium dome.
Planetarium21-alex.jpg|GM-II starfield projector at [[Kerala Science and Technology Museum|Priyadarshini Planetarium]], [[Trivandrum]], [[India]]
Planetarium-alex.jpg|[[Priyadarshini Planetarium]], [[Trivandrum]], [[India]]
Søerne 5.jpg|[[Tycho Brahe Planetarium|Planetarium]], [[Copenhagen]], [[Denmark]]
</gallery>

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 [[Acoustics|acoustic]] and [[Ventilation (architecture)|ventilation]] issues as GRP.
* Most modern domes are built from thin [[aluminium]] sections with ribs providing a supporting structure behind.<ref>{{cite web|title=ESOblog: How to Install a Planetarium A conversation with engineer Max Rößner about his work on the ESO Supernova|url=https://www.eso.org/public/blog/how-to-install-a-planetarium/|website=www.eso.org|access-date=21 February 2018|url-status=dead|archive-url=https://web.archive.org/web/20180507190501/https://www.eso.org/public/blog/how-to-install-a-planetarium/|archive-date=7 May 2018}}</ref> 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 [[joystick]]s in the arm rests of seats to allow audience feedback that influences the show in [[Real-time computing|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 [[Incandescent light bulb|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.

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.<ref name=Aru>{{cite journal|last1=Aru|first1=Margus|title=Under One Dome: AHHAA Science Centre Planetarium|journal=Planetarian: Journal of the International Planetarium Society|date=March–June 2012|volume=41|issue=2|page=37|url=http://c.ymcdn.com/sites/www.ips-planetarium.org/resource/resmgr/planetarian/201206planetarian.pdf|access-date=2017-06-02|url-status=live|archive-url=https://web.archive.org/web/20151002175556/http://c.ymcdn.com/sites/www.ips-planetarium.org/resource/resmgr/planetarian/201206planetarian.pdf|archive-date=2015-10-02}}</ref>