Observing the sun, we don’t need a big telescope for two reasons. One, the sun is a large object, at least compared to other celestial objects, so we don’t need the high magnification that larger telescopes provide. And two, the sun is very very bright, so we don’t need to collect an immense number of photons to gather the information we want. In fact, the sun is so bright that we still need to put solar filters (specially coated mylar film) on top of all of our telescopes so we don’t hurt our eyes or break our cameras (ever used a magnifying glass to start fires in bright sunlight?)
We recently bought new telescopes for our green line experiment. Made from carbon fiber, the 103mm, f/7 system is ideal for observing the sun. When the sun goes into eclipse, the temperature will drop by about 10 degrees. Most telescopes would contract when this happens, changing focus, but the carbon fiber will prevent this and these telescopes should stay in focus. These two telescopes are piggybacked onto each other, so we have nicknamed this our Binocular System.
Mounted onto the back of both of these telescopes are filters in the green spectrum. One is a simple, standard oxygen 3 filter, centered around 540 nm, about 10 angstroms wide. The other is an extremely narrow filter, only one angstrom, centered at 530.2 nm, the emission line for iron 14. This filter will only catch photons from iron 14, so we can be sure we are only seeing the corona.
The cameras that we will use are Atik Titans, with a planetary imaging feature that can sample up to 15 times per second. With the physical restrictions on the system, we can only sample up to 6.3 Hz, which is still sufficient since the intensity oscillations we are looking for happen about two times per second.
Our second experiment is to take an image of the corona in full to study proper motions of the structures. For this white light experiment, we are using a TeleVue Renaissance, a beautiful brass telescope, with surprisingly quality optics. This refractor was designed for wide field observations, perfect for imaging the extended structure of the corona.
Our camera is an Atik 383 L+, a CCD with a large chip. Since the camera is designed for wide fields, the chip fits right in the middle of the flat image plane despite its size, so we will get a crisp image with no vignetting. This camera has a download time of about 10 seconds, meaning we can’t use it for our green line experiment, but it suits our needs for the white light. We will take a series of exposures progressively longer to image both the bright part of the corona close to the sun, and the faint limbs far away. This pattern will cycle during the two and a half minute eclipse, and at the end, we can stitch together all of the images for one spectacular view of the corona’s structure.