Astronomy Department Solar Telescope
In 1977 Jeffrey Baumgardner designed and built a solar telescope for the Astronomy Department. This instrument has been modified over the years, and remains a capable and flexible teaching instrument. The broad capabilities of this telescope allow it to be used in freshman level laboratory exercises (such as Sunspots and Solar Rotation) as well as graduate exercises (Solar Spectrum). If you are interested in more detail about the telescope design, click here.
We’ve added a glass screen that allows a white light image to be projected into the hall:
This allows any visitor to our department to see a nice, big (about three feet in diameter) image of the sun on any clear day.
The telescope can also project this image down onto a tablet, allowing students to record sunspots for laboratory exercises such as determining the rotation of the sun. In another configuration the image is reflected off a grating to display a high resolution spectrum. This is a bit hard to photograph, but here is a combination of two images of the spectrum to get a reasonable amount of the visible spectrum:
The final configuration, and perhaps the most amazing, is the spectroheliograph mode. In this mode the image of the sun is scanned back and forth across the entrance slit to the spectrograph, a line of the spectrum is selected, and an eyepiece is used after the exit slit to observe the resulting image of the sun in a single wavelength. The images below are all in taken in the hydrogen alpha line. The only other line of real use is the calcium K line.
The image is now inverted – you can see the active region around the sunspot now appears on the upper hemisphere.
The horizontal lines are due to either very slight imperfections in one of the slits or dust. Unlike a set wavelength and bandwidth for a instrument such as Coronado’s popular Personal Solar Telescope (PST) – any wavelength can be chosen, and the bandpass adjusted optimize the image for the particular feature of interest. (This can also be used to reduce the visibility of the horizontal lines at the expense of resolution.)
The nature of creation of the image makes it very difficult to photograph (the image is rather faint, it dwells longer at the edges, and the scanning of the solar image interacts with the scanning of the CCD). The eye is more forgiving and sees a more impressive image. With those caveats here are two more images demonstrating what you can see in this mode of operation: