SIRIUS OBSERVATORY
SPECTROHELIOSCOPE
Pictures follow overview
|
OVERVIEW:
|
Some items have a page explaining them -- if so, there will be a link below the picture.
Click any thumbnail for larger picture.
Picture will open in a new window.
Then close the picture; no need to use your browser back button.
NOTE: Larger images will take a little time. Please
be patient!
|
|
|
|
|
|
|
|
![]() One set of Anderson Prisms |
|
|
|
|
![]() Grating mount - note slides, with motor, so it can be moved for focusing. |
|
Details of operation:
The 10" (primary) flat on the outdoor coelostat reflects sunlight (parallel) light to the second coelostat flat. This reflected (still parallel) light is sent horizontally 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 up or down. 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.
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.