Firearms versus telescope mirror!

Telescope mirrors are delicate, right? Dust degrades your image, right? Can a bit of dust damage your mirror?

So what happens when you shoot one with a gun?

Reflector telescopes are a great way of getting some serious aperture onto a deep-space object like a nebula or galaxy. The 10-inch Dobsonians we have give a relatively inexpensive, no-nonsense and, frankly stunning view of those hard-to-see, dim fuzzies, especially from a dark sky location.

New owners of reflector telescopes always ask me how often do they need to clean the mirror. They seem surprised when I tell them that with care, they probably won't ever have to. Mirrors, particularly large ones, are very forgiving.

How's this for a case in point?

The Harlan J Smith Telescope in Texas is a 107 inch Cassegrain (with a Caudé option as well, for the technical). To put that into perspective, the ASV's monster in Central Victoria is "only" 40 inches in diameter. On commissioning in 1968, it was the third-largest telescope in the world.

But in February 1970, there was an "incident". A member of staff appears to have had some sort of mental health episode, and directed his anger (along with a hammer and most of the clip from a 9mm pistol) at the mirror. He succeeded in shooting the mirror seven times, the damage being 3-5cm craters in the surface. Thankfully, apart from some understandable trauma, nobody was hurt.

The telescope was relatively unscathed and was able to be used the very next night. It's been in continuous use ever since, with the mirror undergoing regular maintenance. The damage is still visible, and has reduced the light-gathering ability of the mirror by about 1 per cent. Diffraction from the craters is minimised using matt-black coatings.

So next time you peer at your mirror and consider if you should clean those specks of dust off, think again. You're more likely to scratch it and cause diffraction spikes.

Read the original news story here.

Image: McDonald Observatory