Touring the telescope
While Bill is once more pointing the telescope at the wall (in order to measure the noise in the camera), I thought you’d want to see the telescope that’s providing us with our beautiful images. The WIYN 3.5 m is the most modern of the big telescopes up here, and was opened for business in the mid 90s; as you can see from the image below, it has a very unusual and distinctive structure.
It’s a slightly odd view, but you can see the secondary mirror toward the right of the picture. The primary is to the left, enclosed in that blue box. WIYN’s mirror was one of the first to employ a lightweight, honeycombed design that makes the mirror much thinner than those in previous generations of large telescopes. That makes the telescope rather squat, and its lightweight appearance is complimented by the thin struts that form the telescope body. Before I sound any more like I’m describing your perfect kitchen design, have a look at the back of the mirror:
Each of the little pads you can see are controlled by a separate motor; they’re used for what’s called active optics. As the telescope moves around the sky, gravity will slightly distort the mirror’s shape. The motors can put pressure on the mirror to adjust for this effect – these tiny changes make a difference in our search for the perfect image.The light travels in through the dome’s slit (all observatories have ‘domes’, even if – like WIYN – they’re hexagonal), hit this primary and then bounces off the secondary. In then bounces off a third mirror just in front of the primary and then is reflected to the side, where our camera sits; it lies inside the blue case, cooled to reduce the noise that might interfere with our images.