A lunar eclipse. The top row is comprised of digital photos; the bottom row is comprised of computer simulations rendered by researchers at Rensselaer Polytechnic Institute.
Software magic reveals lunar eclipses
12 Jun 2009
Lunar eclipses are well-documented throughout human history. These rare and breathtaking phenomena—which occur when the moon passes into the Earth's shadow and seemingly changes shape, colour, or disappears from the night sky completely—has captured the attention of poets, farmers, leaders and scientists alike.
Now, researchers at Rensselaer Polytechnic Institute have developed a new method for using computer graphics to simulate and render an accurate visualisation of a lunar eclipse.
The model uses celestial geometry of the Sun, Earth and Moon, along with data for the Earth's atmosphere and the moon's peculiar optical properties to create picture-perfect images of lunar eclipses.
The computer-generated images, which are virtually indistinguishable from actual photos of eclipses, offer a chance to look back into history at famous eclipses, or peek at future eclipses scheduled to occur in the coming years and decades.
The model can also be configured to show how the eclipse would appear from any geographical perspective on Earth—the same eclipse would look different depending if the viewer was in New York, Sydney or Rome.
"Other researchers have rendered the night sky, the Moon, and sunsets, but this is the first time anyone has rendered lunar eclipses," said Barbara Cutler, assistant professor of computer science at Rensselaer, who supervised the study. "Our models may help with investigations into historical atmospheric phenomena, and they could also be of interest to artists looking to add this special effect to their toolbox."
< A "dark" lunar eclipse.
The appearance of lunar eclipses can vary considerably, ranging from nearly invisible jet black to deep red, rust, to bright copper-red or orange. The appearance depends on several different factors, including how sunlight is refracted and scattered in the Earth's atmosphere.
Graduate student Theodore C. Yapo and Cutler combined and configured models for sunlight, the solar system, as well as the different layers and different effects of the Earth's atmosphere, to develop their lunar eclipse models.
For the study, Yapo and Cutler compared digital photos of the February 21, 2008, total lunar eclipse with computer-rendered models of the same eclipse. The rendered images were nearly indistinguishable from the photos.
Another model they created was a rendering of a lunar eclipse coming up in 2010. Yapo said he looks forward to taking photographs of the event and comparing them to the renderings.
One potential hiccup, he said, is the April eruption of Mt. Redoubt in Alaska. Volcanic dust in the Earth's stratosphere can make a lunar eclipse noticeably darker and more brown. Yapo and Cutler's models can account for this dust, but they performed their simulation prior to the eruption, and assumed a low-dust atmosphere.
Adapted from information issued by Rensselaer Polytechnic Institute.
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