Hiding from the light

How do you construct a simple light shield? That’s what multiple people wanted to know after reading one of my recent columns (“Everyday accessories” from February 2014) in which I mentioned you could assemble a barrier separating your telescope from an intrusive light source by using materials purchased at a hardware store. Might I be able to provide them with plans for constructing one? At the time, I unfortunately couldn’t.

Truth be told, there is no cookie-cutter design for a light shield. To determine its final form and size, you must consider a number of factors, including the nature of the light source, the size of the telescope being shielded, and the degree of desired portability. This past spring, after decades of dodging pesky outside lights and dealing with annoying outdoor illumination I sometimes encountered at star parties, I finally put together a lightweight, portable light shield for my 10-inch telescope. Here are the three simple steps I took, which you can modify to fit your particular circumstances.

Step 1: Draw up a design, and decide on the necessary materials. I based my design loosely on a rectangular sail-like shield created by Chris Bayus of Flint, Michigan, and featured in Phil Harrington’s book Star Ware, First Edition (John Wiley & Sons, 1994). Its height would have to be 6 feet (1.8 meters) to effectively screen my telescope when pointed at the zenith. Meanwhile, the width would have to cover the distance difference between the eyepiece location in this zenith position and its location when the scope is aimed toward the horizon (4 feet [1.2m]). My completed light shield would be composed of a 4-foot by 6-foot frame held upright with a pair of struts that would support the actual shade (a 6-foot by 8-foot [1.8m by 2.4m] tarp attached to the frame with bungee cords).

Because portability was a critical factor, I chose to work with 1-inch-diameter (2.5 centimeters) PVC plumber’s pipe and non-threaded “slip-in” fittings (90° elbows, tees, and end caps). This material would produce a lightweight shield that would be easy to assemble and break down for travel purposes. Four-foot and 6-foot pipes would form the frame, connected at the top with two elbows and at the bottom with a pair of tees. I would assemble each of the support struts from a pair of 18-inch (46cm) lengths of PVC pipe joined in the middle by a tee and closed at the ends with slip-in caps. A 1-inch segment of PVC pipe would connect the tees in the support struts to the tees at the base of the frame. Then I would drape the tarp over the top of the assembled frame and secure it with bungee cords.

Step 2: Construct the light shield. At a local hardware store, I purchased the necessary PVC pipe and fittings, plus the tarp and some PVC adhesive. A hacksaw sufficed to cut the different lengths of pipe, which fit snugly into the fittings. To avoid the risk of arriving at a star party minus a few key pieces (the entire framework consisted of 20 pieces), I glued the elements making up each of the sides of the frame (6-foot pipe, elbow, and tee), as well as the component parts of each support strut. These four pieces, along with the two 4-foot pipe sections that make up the top and bottom of the frame, plus the tarp and bungee cords, fit nicely in my car and assemble in a matter of minutes.

I don’t pretend to be a master carpenter, and I don’t have an engineering degree, but I had to admit that the final product looked pretty good. But would it work?

Step 3: The field test! Just days after finishing my light shield, I took it to a star party at a nearby high school. On a previous visit there, I’d been completely frustrated with an obnoxiously bright outside light whose glare made it impossible to locate and view anything but the Moon and planets. Up went the light shield, and I was in business. I successfully picked up the Hercules Cluster (M13) even though it hovered above the part of the school building that housed the light.

If extraneous outdoor lights have spoiled your backyard astronomy adventures, fight back — with ingenuity and a little engineering! A few hours spent making a light shield will bring you and your telescope back into action. To obtain detailed information and photos outlining the construction of my light shield, download the PDF below.

Questions, comments, or suggestions? Email me at gchaple@hotmail.com. Next month: We take a peek into the Struve double star catalog. Clear skies!