SIRIUS OBSERVATORY
SPECTROHELIOSCOPE
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OVERVIEW:
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![]() One set of Anderson Prisms |
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Details of operation:
The primary (10") flat of the coelostat reflects sunlight (parallel) light to the second (8-3/4") coelostat flat. This reflected (still parallel) light is sent downwards to an 11" flat, then reflected to the 6" F50 lens. The light then travels 25 feet to form an image on the first slit. Just before it hits the slit, though, it goes through a rotating square prism. One of the 6" F27.5 mirrors is focused on the back side of the first slit. It takes the image and turns it back into parallel light, reflecting it on the 4" grating. The grating reflects whatever wavelength you want to look at, which is accomplished by moving it left or right. The second mirror is focused on the grating, and takes the parallel light and turns it back into an image, reflecting it to the back of the second slit. On the front side of this slit is the second square rotating prism, then an eyepiece which is focused on the slit. I can control the motors for guiding, focus, and change speed of the rotating prisms all from the eyepiece. This took some extra wiring and switches, but makes it useable by one person now.
What happens:
Sunlight is divided into many different wavelengths by the diffraction grating. By moving the grating, you can see whatever wavelength you want to view in the eyepiece. The rotating prisms simply build up an image, much like television camera makes a "picture" by scanning several hundred lines, one at a time, then projecting them in sequence on your screen. This happens so rapidly that your eyes make it seem like you are looking at one picture. The slits are only opened a thousandth of an inch or so, so you would see a very tiny slice of the sun at one time were it not for the rotating prisms.