You crash land on a planet with technology as advanced as Earth — in the 16th century. Drat! You need to see the night sky to get an idea of where you are. What planets can you see, what stars, constellations? Is the Enterprise in orbit?

As a member of Starfleet, the prime directive gets in the way of you creating something really fancy (and your shuttle blew up, so no help there). You are in what in space speak is called…a pickle. Okay, that’s not space-speak, that’s your grandparents talking. But hey, they were some of the original Star Trek fans.

So how do you study your celestial surroundings, with some of those stars burning bright over 12 quintillion (that’s 15 zeroes) kilometers away? Use lenses to bend light your way.

• 2 magnifying glasses (plastic ones are fine)
• Magnifying mirror
• Index card
• Pencil
• Scissors
• Tape
• Flashlight (an LED flashlight is not a good choice, but will do in a pinch)

1. Place the light bulb end of a flashlight on an index card. Draw a circle and inside that circle draw a simple shape, such as a star or an arrow. (Or even your initials.)

2. Cut out the circle. Then cut out the shape you drew inside the circle. Tape the circle (with the cut out shape) to the front of the flashlight.

3. Set up the flashlight so it shines on a wall. This is your star. It’s easier if you have a friend to hold the flashlight, but placing it on a chair will do.

To make a refracting telescope:
4. Hold the magnifying glass (this is what’s called the objective lens) with one hand so the light makes a blurred spot on the wall. Put your other hand in the beam of light and move it toward the wall, away from the objective lens. Stop when you see the cut out shape shining in your hand. This is the focal point of the objective lens.

Now pick up the second magnifying glass. This is your eyepiece lens. Hold the eyepiece lens at the focal point (where your hand stopped). Slowly move the eyepiece lens closer to the wall until you see the cut out shape.

To make a reflecting telescope:
5. Place the mirror so it faces the wall. Point the flashlight at the mirror so that its light reflects onto the wall. (We set the mirror on the floor, with the flashlight on the floor in front of it, but propped up on a notebook.) Place your hand in front of the light reflected from the mirror. Move your hand toward the wall until you reach the focal point. Replace your hand with the eyepiece lens (a magnifying glass) and move it toward the wall, stopping when you see the cut out shape.

You made two types of telescopes, and maybe it’s the first step to figuring out where you are.

The refracting telescope uses two lenses. The lenses are convex (or curved outward). The objective lens refracts, or bends, the light onto the focal point. The eyepiece bends it back straight again except now the image is inverted. So don’t worry if you spot the Enterprise flying upside-down.

The reflecting telescope, however, uses a concave (or curved inward) mirror instead of an objective lens to reflect light onto the focal point before it passes through the eyepiece lens.

A big refracting telescope needs a big objective lens, but big lenses are heavy and expensive to make. The Yerkes Observatory in Wisconsin uses the world’s largest refracting telescope: the objective lens is 102 centimeters across and weighs 225 kilograms!

Reflecting telescopes can be much bigger. The Gemini Telescopes in Hawaii and Chile have mirrors 8 meters across.