Our eyes are good enough for simple stargazing. But they tell us very little about what the stars are really like. To see the stars more clearly and find out about them, we need to look through a telescope. The word telescope means 'see far', and that is just what a telescope enables us to do. The Italian scientist, Galileo Galilei, was the first person to look at the heaven through a telescope. Galileo made his telescope using glass lenses. Some astronomers still use this type of telescope today. It is called a refractor, because the lenses refract or bend the light coming in. But the biggest and most powerful telescopes use mirrors to gather the sunlight. They are called reflectors, because the mirrors reflect the light coming in. Buy your lenses from an optician or hobby shop. Tell the assistant what you want them for. Ask for one with short focal length (A), the other with a long focal length (B).
Steps to be taken
1. Fit lens A into the end of the smaller tube and fix it in a position with sticky tape. 2. Fit lens B into the end of the larger tube and fix as you did it for lens A. 3. Slide one tube inside the other. 4. Look at the distant object and slide the smaller tube in and out until you get a sharp image. The telescope is now in focus. It will give you an upside-down image. But this doesn't matter if you are looking at the stars.
Two lenses which bulge in the middle
Two cardboard tubes, one able to slide into the other