How to Build a Telescope

Get inspired by Galileo and turn an old pair of glasses and paper towel rolls into a Galilean telescope. This fun, recycled STEM project teaches kids about how lenses work and inspires them to dream big about space, innovation, and more.

Build a telescope with this fun recycled STEM project and learn about Galileo, lenses, and more.

What is a Telescope?

A telescope is a device that people use to see objects that are far away, such as stars and planets. Telescopes use optics like lenses and mirrors to gather and focus light from the sky. The bigger the lenses or mirrors, the more light the telescope can gather and the further away you can see.

This project builds a refracting telescope using magnifying lenses from an old pair of reading glasses. This is the same kind of telescope that Galileo Galilei built way back in 1609. His telescope magnified the stars about 20 times.

illustration of galileo galilei holding a telescope while standing on the earth with blue starry sky background

How Does a Refracting Telescope Work?

There are two lenses in the telescope. One lens is responsible for bringing light into your eyes. The other lens is responsible for magnifying the image you see. These lenses inside are called optics and mimic the lenses you have inside your eyes. When you look through this telescope, the image is upside down, just like in Galileo’s telescope.
Modern-day telescopes use mirrors instead of lenses because the lenses required to see distant space are too big and heavy for use. It’s also a lot easier to build a perfect mirror. If lenses have any flaws, the image seen in the telescope will be flawed as well.

Let’s Talk About How Lenses Work!

This project uses both lenses from a pair of glasses, but to make the telescope work you need to know which way to place the lens.

A concave lens is a lens that has an inward curve on one side. They are called diverging lenses because they spread the light into a wider beam. People who need to improve their far-away vision have glasses with concave lenses.

A convex lens is a lens that has an outward curve on one side. They are called converging lenses because they focus the light into a narrower beam. People who need to improve their close-up vision have glasses with convex lenses like the reading glasses in this telescope.

DIY Telescope Supplies Needed

This project is a great opportunity to use some recycled supplies. Raid the bin for paper towel rolls. Reading glasses can often be found at reuse centers or second-hand stores. Look inside the temple pieces for the magnification.

how to make a refracting telescope - two paper towel rolls, black eyeglasses, yellow masking tape, and orange handled scissors on blue paper

One pair of reading glasses (at least 2x magnification, we used 4x)
2 cardboard paper towel rolls
Scissors
Masking tape

How to Build a Telescope with Reading Glasses

Carefully pop out lenses from the pair of reading glasses.

how to make a telescope - black eyeglasses on blue with lenses removed and laying underneath

You need one paper roll that is larger than the other so you can slide one inside. If your rolls are the same size, cut a slit down the middle and overlap one edge over the other. Tape to secure. Skip this step if you have two different diameter rolls.

how to make a telescope - paper towel roll with a slit down the side with eyeglass lens and orange handles scissors sitting underneath on blue paper

Tape one of your lenses with the convex side out to the end of the smaller paper roll. Secure well, trying not to cover too much of the lens with the tape.

how to make a telescope - End view of paper towel roll with lens taped to end with yellow masking tape. Roll is sitting on yellow tape roll on blue paper

Repeat step 3 with the other glasses lens and the other paper towel roll. Be sure the convex (curved out) side of the lens faces out.

diy telescope - two paper towel rolls with ends taped with yellow tape plus yellow tape roll on blue paper

Now insert the small roll into the larger roll so that a lens is on each end. Look through the smaller lens. To focus the image, adjust the length of the telescope by changing how much the small roll is inserted into the larger roll.

Finished paper roll telescope with yellow tape and lens on end with black eyeglass frames sitting on top on blue paper

What do you see when you look through the lens? The image is upside down, just like in Galileo’s telescope. Modern-day telescopes use mirrors to reflect the image right-side-up.

More Space-Themed Fun for Kids

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Then try these Felted Ball Planets. They’re a super-fun craft project that teaches kids how to felt wool. Plus it helps them get their wiggles out! They’re a sneak peek into our STEAM Explorers Space Ebook Unit Study.

Join us as we explore SPACE with STEAM Explorers!! Kids will love making a DIY telescope, crafting a solar system, making the Earth orbit and rockets fly, and so much more! You'll love the helpful standards-based learning, printables, and tools that make STEAM (science, technology, engineering, art, & math) exploration easy!

What's Inside the Space Ebook Unit Study by STEAM Explorers:

Inside every STEAM Explorers ebook are:

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