On August 17th Insight Media had a chance to get a tour of the Hayden Planetarium at the American Museum of Natural History. This behind the scenes tour was arranged by the Mid-Atlantic Chapter of SID. Matthew Dougherty, a consultant to the Rose Center for Earth and Space at the American Museum of Natural History served as our tour guide.

Matt Brennesholtz
Insight Media Analyst

The tour started with the normal planetarium show, "Cosmic Collisions." To my disappointment, this planetarium show was done exclusively on the 7 Barco CRT projectors. The Zeiss Universarium Model IX planetarium projector, also known as a starball, was not used. In fact, it was not even visible since it is stored under the floor of the planetarium theater. After the normal visitors left, Dougherty raised the starball from below the floor, an impressive operation in its own right for a $4.5 Million projector. After the projector was raised, Dougherty explained all its features to us. It can make over 10,000 stars, some so dim it is necessary to use binoculars to see them. It also projects diffuse objects such as the Milky Way and the large and small Magellanic Clouds. The projector also includes 8 small projectors that can show an image of any object anywhere on the dome. One of these projectors is dedicated to the Sun, one to the moon, and the remaining six can be used for any object in space. This limits the planetarium to showing a maximum of six of the eight (nine for traditionalists) planets simultaneously.

After showing off the projector, Dougherty had us take seats and he dimmed the lights and activated the starball. He demonstrated all its features, including its ability to show the sky from any point on earth at any time, night or day. For example, he demonstrated a solar eclipse, where no stars are visible as the moon takes an increasing slice out of the sun. As the moon blocks the whole sun, the daytime stars suddenly become visible, along with the sun’s corona. Dougherty could also adjust the ambient light to show stars visible from New York City (about 7) New York suburbs (about 100) and a remote mountaintop out west, where all 10,000 would be visible, if you had your binoculars. He also showed the solar system from the Sun’s north pole, where the 6 inner planets could be seen moving in their near-circular orbits around the sun. He pointed out that Mercury’s orbit was the only one that was visibly elliptical to the naked eye.

After the tour, he lowered the starball and took us out into the lobby to answer questions, since the Planetarium dome was needed for the next normal show. He said that of the four mainstream shows oriented towards children and tourists in the planetarium since it opened in January 2000, only two of them used the Zeiss Universarium. One of the reasons for this is the time to raise and lower the starball, about 2 minutes each. For safety and traffic pattern reasons, the starball must be below the floor when people enter and exit the planetarium and the time taken to raise and lower it cuts significantly into the 30-minute program. Dougherty said the starball was used in special programs open to the public on Monday and Tuesday nights. These programs are often led by professional astronomers presenting their latest research.

Most main shows are presented by the seven Barco CRT projectors, five to fill around the periphery and two to fill the center of the dome. These projectors were installed when the planetarium opened in 2000. The tubes have been replaced periodically, but the projectors are reaching the end of their life. The AMNH has bought 12 SEOS Zorro projectors to replace the CRT projectors. Each of these QXGA projectors uses 4 LCoS panels from Gemidis. Three are used in a normal RGB configuration. This RGB image is relayed to the 4th panel to improve the black levels before projection onto the dome. The net result is 500,000:1 contrast, according to SEOS. No lumen output value is published by SEOS for this projector.

The Zorro projectors will be used in pairs, primarily to increase the brightness but also to serve as an on-line backup. Five projector pairs will be used to fill the periphery of the dome and the sixth pair will fill the center. An earlier generation Zorro projector had been temporarily installed in the planetarium more than a year ago for tests. Dougherty was enthusiastic about it, especially about its sharpness of focus and very high contrast. For one test, they turned off one of the CRT projectors and turned on the Zorro projector. The Zorro projector matched the very dark blacks produced by the CRT projectors with sharper focus. When a star crossed the boundary between the two images, it suddenly became noticeably clearer and sharper, according to Dougherty. While Insight Media has no way to validate a 500,000:1 contrast claim, any projector that has contrast equal to or better than a high-end professional CRT projector has very high contrast indeed.

For an expanded version of this article, including the bad news about the Zorro projectors, see the September issue of Projection Monthly with Flat Panel Coverage.

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