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.
I was wondering whether there was adaptive optics
on the telescope you’re using. That should help
with better definition and suchlike. Do you use
a laser pointed at the sky to help measure atmos-
pheric disturbance? If so, I would be interested
to know what that involves. Keep up the good work!
Is that silver gaffer, or duct, or cloth tape in the bottom right? It gets everywhere!
Rick – WIYN has some low-order active and adaptive features. The plumbing behind the primary mirror is actuated to keep the mirror properly shaped as temperature and gravitational stresses change (referred to as active optics). The camera we’re using incorporates what some cal first-order adaptive optics, following the motion of the image centroids with measurements 20 times per second when there are bright enough reference stars in the field. Laser AO systems are used mostly on lager instruments (although the USAF has two telescopes this size well equipped for AO), and I don’t think lasers have ben used at Kitt Peak. One reason may be aircraft avoidance – there’s a lot of civilian and military traffic nearby, which would require shutting down the laser frequently.
You can’t have leading-edge technology without duct tape. As the astronauts of Apollo 17 found out, it even works on the lunar surface.
Thanks for that info. Naively, I hadn’t realised
that the US Air Force has its own telescopes. I
guess they need their own, thinking about it. Does
anyone know if they publish some of their ‘research’ findings in papers and suchlike?
Interesting to note that duct tape is used outside
of the ventilation and entertainment industries.
Worth the weight.
That is slightly more complicated than my telescope.