A planetarium projection system technology wise can be:

• Opto-mechanical/ Star-ball (analog)
• Digital
• Mix of Opto-Mechanical and Digital i.e. Hybrid.

When it comes to digital projection systems there are three choices optics wise -

• Spherical Mirror/ Mirror Dome System (placed on the circumference/ cove of the dome).
• Multiple Projectors System (placed on the circumference/ cove of the dome).
• Fisheye Projector System (placed on the centre of the dome).

Spherical Mirror (mirror dome) system is the cheapest among the above three but has following shortcomings in comparison to the other two.

• Mirror Dome cannot create full sky/ dome and suffers from truncation (part of the sky is missing) thus defeating the very objective of a planetarium. In fact these systems are suitable for unidirectional viewing.
• Projection quality is not as good because of the intrinsic limitations of the mirror optics.
• Non availability of compatible and up to the mark real time render planetarium sky simulation software (PSSS) for mirror domes thus again defeating the very purpose of a planetarium.
Note:

• Quite recently planetarium industry has introduced 3D planetarium systems where audience wears 3d glasses in the planetarium. However, their utility is highly debatable at this point of time not only due to the fact that they are too costly and there is hardly any 3D planetarium content that is available but a digital planetarium by virtue of full dome projection is already a 3D immersive environment.

A multiple projectors system to create full dome/ sky in a planetarium is primarily used to achieve higher brightness levels across the dome by adding up the individual brightness capacity of the projectors. Since now single digital projectors with small foot print (compact), very high brightness, contrast and resolution are available, one can achieve full dome/ sky projection with single projector mated with a suitable high quality fisheye lens especially for domes up to 12 meter diameter (about 120 reclining chairs) and there is no need to align, blend, maintain and upgrade multiple projectors. In recent years due to fisheye optics, free ware technologies usage and modular designs the scenario has changed drastically in favour of the user/ audience especially educational institutes as the planetariums have become cost effective and easy to operate, maintain and upgrade. In fact digitalization of mobile planetarium became possible only due to fisheye optics technology. Single Projector (Fisheye optics) system with DLP with modular design and a user friendly console which can be even tablet based actually liberates a planetarium from the obstructions and bulkiness associated with multiple projection system. The planetarium educator is free from operations hassles and can now focus on his prime responsibility i.e. the content and audience. Among the fisheye systems Laser technology has even better quality output than DLP however, laser projection is not only quite costly to buy and maintain especially in a developing nation but also suffers from large foot print and the projector may have to be placed quite high from the ground thus obstructing the full dome/ sky view. At present the laser fisheye planetarium projection systems are not prevalent, the world over. Majority of the planetariums that are being set up now days the world over especially for dome diameters up to 12 meters have single fisheye projection system. Due to the paradigm shift, Planetarium EducationTM is no longer a prerogative of the developed nations. In fact the decision makers can now implement Planetarium EducationTM at grass root levels in a cost effective way and can even scale it up to the desired demographical and pedagogical levels.

Among the various digital projection technologies like LCOS, LED, DLP, LASER, etc DLP is most prevalent and tested in planetarium industry the world over as:-

• LCD though cheaper suffers from screen door effect (i.e. fine lines separating the projector's pixels become visible in the projected image) which is not suitable for planetarium use.
• LED projectors though cheaper and even have longer lamp life up to 20,000 hours (thus low maintenance cost) does not have high brightness/ lumens (at this point of time), thus not suitable for planetariums having more than 7 meter diameter
• LCOS though have high contrast ratios like DLP but again like LED has low brightness/ lumens.
• LASER has no shortcoming as such for planetarium purpose except for the fact that there prices are astronomical, they are bulky and their maintenance and running cost is too high.
Remember :

• The quality of a digital projector is measured primarily in terms of its resolution and contrast ratio.
• Higher the contrast ratio and resolution better it is for the planetarium projection.
• Bigger the dome brighter has to be the digital projector. Brightness of a digital projector is measured in lumens.
• A higher resolution and a higher contrast ratio would mean better projection quality primarily in terms of darker skies and point/ dot stars.
• For higher and higher resolutions the improvement in projection quality becomes quite subjective to the human eye.
• The DLP technology has intrinsically better contrast thus darker skies.
• The lamp/ bulb of a digital projectors is a consumable part as it evolves with time and becomes dimmer and dimmer and is to be eventually replaced.
• It is the native resolution of a projector that matters. Higher non native resolutions are of no use.
• Beware of the projector advertising 1: 50,000 or more contrast ratio as it is based on automatic Iris which is useless in planetarium projection as while projecting stars the contrast falls down to 2000:1 or even less.
Note:

• Quite recently Laser, DLP and LED Hybrid projectors with small foot print (compact) and quite high lamp life have been successfully tested in the mobile planetarium industry.

It is the soul of a planetarium. Primarily speaking it has an extensive and accurate data base of heavenly bodies like stars, deep sky objects like galaxies, nebula, etc, solar systems objects, like planets, moons etc. It creates full dome scenarios of the sky from the Earth, Space and various other Celestial Bodies at different times.

In addition to the real time render the user would also need:

• Images which can be full dome or in perspective mode,
• Panoramas,
• videos which can be full dome or in perspective mode,
• music

It means various characters, locations and examples that we use in our shows are local and embedded in Indian ethos rather than in a voice over of foreign characters at foreign locations. For example show titled :

• "Celestial Gymnastics" covers celestial merry go round from different locations on the Earth including from the City of Taj Mahal.
• "Galileo's Sky/ History of Astronomy" includes contributions from Aryabhatta, the great Indian mathematician astronomer.
• "Chanda Mama/ Our Nearest Neighbour" is about changing shapes of the Moon and how they are related to various festivals celebrated in India.
• "Dhruva Tara" has ancient sky culture story from India about the brave boy named "Dhruva" who became the pole star.
• and a whole of lot more....

We also cover heavenly bodies related festivals like Easter - Christian (the first Sunday after the full moon following the March equinox) Holi-Hindu (Full Moon) Gurupurv - Sikh (Full Moon) Budh Purnima - Buddhist - Full Moon Eid - Muslim (Crescent moon) and a lot more... And last but not the least The cure for a fallacious argument is a better argument, not the suppression of ideas. ...........Carl Sagan

The planetarium technology now days has become quite user friendly. Its digital and plays pre-recorded shows. It is plug and play. However, it is not only the right technology but the capabilities of an educator/ planetarian that makes a planetarium endeavour a success. A carefully planned and rehearsed live show is the most effective thing in a planetarium and in order to achieve it a planetarian ideally should -

• have teaching experience.
• have educational background in science/ mathematics/ computers (preferably physics) at graduation level.
• have idea of star gazing.
• be a computer literate.

Remember! a planetarium is a cinema, theatre and school all rolled into one. Last but not the least the training of an educator/ teacher and continuous support by the supplier on content development is very crucial to the efficacy of a planetarium.

This increases the minimum possible time gap between two consecutive shows. Besides the attached door increases the weight, volume, inflation time and maintenance cost of the dome unnecessarily. Because of more weight and size such domes are cumbersome to pack or unpack.

A fixed planetarium is often perceived and promoted as a tribute to history of science, our understanding of the heavens above and achievements of human space endeavours. In a way it epitomizes science and technology from the point of view of a common man. The architectural ambience of a planetarium in a city's skyline often reflects the same in an epic form. The outside surface of a planetarium projection dome screen is always hidden as it is enclosed under a protective structure that is usually of brick and mortar called envelope/ shell. It is this envelope/ shell that is designed from aesthetics point of view to give a fixed planetarium a suitable epic ambience. The envelope need not necessarily be dome shaped. Decision makers, for the envelope's ambience, can also choose from many cost effective options that are now days available for example aluminium composite panels (ACP). The ACP construction also takes less time to construct.

A planetarium uses fixed reclining chairs that are usually grouted to the floor. The floor is carpeted to have better acoustics. Seating arrangement/ direction is primarily governed by the fact whether the content/ shows are full dome (astronomy based) or unidirectional (non astronomy based) and accordingly is co-eccentric facing the centre of the dome or unidirectional facing one side of the dome. The former is more suitable for astronomy oriented content. The reclining angle is usually 30 to 45 degrees. For full dome more the reclining angle better it is however, higher reclining angle will have an adverse affect on the seating capacity.

For fixed domes smaller than 7 meter diameter it would be better to have the audience seated on the floor/ carpet just like in a mobile planetarium.

It is designed to empower educators/ institutions to use a planetarium as frequently as they want to cover astronomy topics from very basic to advance levels and even extend the sphere of planetarium to non astronomy topics like geography, earth science, space science, and a whole lot more. The idea is to support planetarium educators/ institutions/ science centres on effective and the fullest use of the planetarium technology so that the planetarium rather than working on novelty alone works on :

• Pragmatic, cost effective, easy, regular and widespread basis so that the conspicuous lacuna of astronomy in the education system can be filled effectively
• Sky simulation that liberates the teaching fraternity from the impediments associated with empirical astronomy.
• Customized content as per the age, ethos, acumen and syllabus of the students/ general public.
• Content that is pedagogically scale-able to a desired level.
• Content that is supported by booklets/ Maps/ Handouts/ Activities/ Quizzes/ Competitions based tests.

It consists of images, panoramas, videos clips, real time render clips, music that can be downloaded at user end and can be played on the dome as and when required. Various support material like scripts, booklets, hand outs, tests, maps, etc can also be downloaded at user end for distribution among students/ audience. It also provides support for content development in companionship to training and otherwise also and technical support for the system till the life of the system.