Greetings, friends. (XXXII)

Greetings, friends. Today I learned from the Actual Astronomy podcast that Terence Dickinson, the Canadian amateur astronomer, passed away a couple weeks ago. He was best known as the author of Night Watch: A Practical Guide to Viewing the Universe, and co-author of The Backyard Astronomer’s Guide.

When I got into the hobby of visual astronomy a dozen years ago, Dickinson’s books were among the first I purchased on the subject, since they were the most universally recommended, and rightly so. Dickinson’s patient and encyclopedic advice informed a generation of amateur astronomers, including me.

My first telescope, an 8” Dobsonian, was one that I basically purchased at Dickinson’s recommendation. If you want to see deep sky objects, you need to maximize the diameter of your primary optics, since that’s what’s gathering all the light. The Dobsonian telescope is a modern take on the old reflecting telescope designed by Isaac Newton about 350 years ago.

Basically, a giant chunk of silvered glass ground into a concave parabola sits in the bottom of this thing, and focuses the incoming light on another mirror near the top of the optical tube that’s mounted at a 45º angle. This angled mirror redirects the collected light out the side of the scope to an eyepiece assembly that magnifies and focuses the image.

So far this is all as God and Newton intended it. The Dobsonian aspect, named for its inventor John Dobson, comes in the form of the telescope mount, which is basically five cleverly cut and assembled pieces of particle board, that provide an smooth altitude-azimuth mount on little Teflon runners. You just grab the end of the optical tube and point it at what you want to look at. It’s simple, easy to use, and it could hardly be cheaper and still hold up the 40 lb. optical tube assembly.

It turns out that a big piece of silvered glass is way cheaper to make than a comparably sized lens, since you only have to polish one side, and the optical quality of the glass doesn’t matter much. Since the size of the primary optic increases with the square of its radius, doubling the size of your optics basically quadruples the price, all else being equal. Except that it gets worse, because economies of scale decrease as the size goes up, since fewer such telescopes are made. An 8” aperture represents the sweet spot where the optics are big enough to pull in deep sky objects (e.g. galaxies and nebulae) but are still small enough to be basically mass produced.

(Incidentally, while Dobson was best known for the eponymous telescope mount, he was also a co-founder of the San Francisco Sidewalk Astronomers, and apparently active until his passing in 2014. I never got to meet him, sadly — but the SF Sidewalk Astronomers had a lot to do with how I got into the hobby in the first place. More about that later, probably.)

I still have my Dob, and although it’s a pain to lug around, it’s still my main jawn. The one thing it’s not good for is astrophotography.

Buying a telescope that was useless for astrophotography was something I did on purpose. If I recall correctly, Dickinson acknowledged the temptation but discouraged beginners from jumping right into astrophotography, because finding your way around the sky is hard enough without also trying to photograph the sucker. I decided at the time that I didn’t need two hobbies where the sky is literally the limit on the amount of money you can spend on gear. I don’t regret it.

Anyway, I learned all that from Terence Dickinson, and more. He was a classic Canadian educator: understated, earnest, dryly funny, and quite serious. The IAU named asteroid 5272 Dickinson to honor his “ability to explain the universe in everyday language.” May his memory be a blessing.

If you’re reading this, I send my love. I hope you go outside on a clear night sometime soon, and look up.