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Fast, High-Resolution Cameras Image the Sun's Surface

Photonics Spectra
Apr 1997
Ruth A. Mendonsa

To the average person, the sun is a celestial body around which the Earth and other planets revolve. It's a source of warmth and light. Many don't realize that the sun is a star, and an interesting one at that.
But researchers at the Big Bear Solar Observatory on California's Big Bear Lake are well aware of the fascinating phenomena that occur on the sun's surface, and they are using photonics technology to acquire a better understanding of them. They are studying how natural phenomena occur, why they occur and exactly what it is that they are seeing. "Most people don't realize the sun is as interesting as it is," said Hal Zirin, the observatory's director and a professor of astrophysics at the California Institute of Technology, which operates the facility."
The group studies phenomena such as sunspot activity by capturing high-resolution continuous images of the surface of the sun. The observatory is equipped with three main telescopes: A 6-in. refractor telescope monitors the whole sun, while larger 26-in. reflector and 10-in. refractor telescopes observe limited regions with high magnification. The telescopes are equipped with special filters that isolate small portions of the optical spectrum, notably hydrogen, helium and calcium.

'Candid camera'
Each telescope is fitted with a Model 1.4i, 1.6 or 4.2 Kodak MegaPlus camera, the latter of which delivers images with resolution of 4.2 million pixels per inch. (An enhanced version of the MegaPlus 4.2 won a Photonics Circle of Excellence Award in 1996.)
The MegaPlus cameras replaced a low-resolution video capture system and a system at the observatory based on 35-mm stop-motion film.
"The electronic cameras are designed for computer image enhancement, manipulation and analysis. As a result, we are now able to obtain the kinds of images that are helping us to learn and understand more about the sun," Zirin said.

The cameras are used with a frame grabber and custom image processing software written by Cal Tech personnel. Images are continuously captured by the cameras and fed into a computer system for recording, viewing and storage. The scientists can view images from any of the telescopes on a single monitor, alternate between images and adjust and enhance exposures.
Among key findings at this facility is the ability to predict the level of sunspot activity. When sunspots collide or rearrange their fields, the resulting solar flares shower the Earth with high-energy particles that can affect communications, power transmission and possibly climate. Last summer, when a sunspot was observed, the facility put out a "Bear Alert" to several hundred locations worldwide advising that there was a rapidly growing sunspot. The resulting solar flare was the largest in several years, Zirin reported.
The images taken at the facility are posted daily on the observatory's Web page at

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