I Built My Own Telescope


Only two hours after I had gathered the parts, some coming from as near as the trash can and broom closet, I was aiming my homemade telescope into the night sky. At first all I saw was a bunch of smeared blotches, but by moving the eyepiece in and out I was able to focus my telescope, and what a spectacle opened before my eyes! I saw four of Jupiter’s moons, not to mention the huge planet itself, craters on the moon, and the rings of Saturn. As the year progressed, I was able to see the crescent of Venus and the white polar caps of Mars. I even saw the white oval of our nearest galaxy, Andromeda, the nebula in Orion, and the Pleiades (a cluster of stars shining through some interstellar gasses). I saw double stars, the Milky Way, and many other beautiful celestial bodies. I even tried looking at the sun, but it didn’t take long (about a millioneth of a second!) for me to find out that looking at the sun is not a safe thing to do! I managed to get around the problem, without buying a special sun filter, by projecting the sun’s image onto a piece of paper. I held a piece of white paper behind the telescope, about four inches away from the eyepiece, and much to my surprise, there was the sun. It was a very bright circle with little black dots covering its surface. I later learned that these dots were sun spots, regions on the sun’s surface where the temperature is somewhat cooler.

The telescope I built was a very simple one. It consisted of one big lens that I attached to the front of a mailing tube and two smaller lenses out of which I built an eyepiece that slid into the bigger tube. The big lens was salvaged from an old camera, while the two smaller lenses were toy magnifying glasses I bought from the drug store. I even hammered three broom sticks together and made a simple yet sturdy tripod on which I mounted my scope.

It wasn’t long until I ached to see more of the night sky, and to see it bigger and brighter! Checking into my wallet and making arrangements with my parents, I managed to get enough support to build a big telescope. Larger telescopes are expensive if bought new, but I planned to build my own for a fraction of the retail cost. The most economical type of telescope is called the reflecting telescope. It gets its name because it reflects and magnifies images by using a curved mirror. (The refracting telescope, like my first one, refracts or bends the light through a lens.) These mirrors can be ground by hand, using materials that can be purchased in a kit for as little as an eighth of the cost of a prefinished mirror. The mirrors vary in size, the bigger the better. A good size to start with would be a four-inch or six-inch mirror, keeping in mind that although a sturdy square box would do for a while, a tube will eventually be necessary to contain the mirror. In reflecting telescopes, the mirror is at the bottom end of the telescope, unlike a refracting telescope that has the big lens at the front of the tube. As light enters the telescope, it hits this mirror and is reflected back to a focal point where it is then intercepted by another mirror. This secondary mirror is turned at a 45-degree angle so that the light that is intercepted will bounce out the side of the tube where the eyepiece will magnify it.

In these larger reflecting telescopes, you must align the curved mirror with the secondary mirror and eyepiece. A special mount must be built that will support the mirror as well as allow for its adjustment. I used a disk of wood a little larger than the mirror with four holes, evenly spaced, drilled along its outer edge. I fitted thumb screws through these holes, and held them tight against the mirror with springs. Then it was an easy matter to turn the screws and line the mirror up with the eyepiece.

A solid mounting is needed to keep the telescope aimed at the same place all the time. A wide pine board, two or three feet high and three or four inches wide, serves very well. You can attach three legs perpendicular to the pine, or a large, square piece of wood or metal, and your base is finished. A tripod can be used, but I have found that with reflecting telescopes, a tripod raises the telescope so high I can’t see into the eyepiece.

By building a telescope, I learned a lot about optics and the hidden treasures that they help reveal in the sky. And by building it and not buying it new, I cut down the total cost of a new telescope to less than half.

Before launching into space with a telescope, keep in mind a few things. Make sure the sky is clear, the air is still, and you are dressed for the weather. You should know where to look for the more important stars that are listed for each month in any almanac, handbook of the stars and planets, or the magazine Sky and Telescope.

And above all, watch out for falling stars.

[illustration] Refracting Telescope, Lens; Tripod; To adjust mirror angle, Springs, Curved mirror; Reflecting Telescope, Mirror, Eyepiece