 Imagine a clear evening when a full moon is just starting to rise. Even though the Moon might seem large and close, it is still too far away for you to see the details on its surface.

 When you look at an object, only some of the light reflected from its surface enters your eye. Much of the light is reflected in other directions.

 As the object moves farther away, the amount of light entering your eye decreases. As a result, the object will appear dimmer and less detailed.

 A telescope uses a lens or a concave mirror that is much larger than your eye to gather more of the light of distant objects.

 The largest telescope can gather more than a million times more light than the human eye.  Objects seen at a distance can be seen much brighter and in much more detail.

 A commonly used telescope is the refracting telescope.  A refracting telescope uses two convex lenses to gather and focus light from distant objects.

 Incoming light from distant objects passes through the first lens, called the objective lens.  Light waves from these objects are nearly parallel to the optical axis of the lens.  The rays form a real image at the focal point of the lens, within the telescope.

 The second convex lens, called the eyepiece lens, acts like a magnifying glass and magnifies the image.  When you look through the eyepiece lens, you see an enlarged, inverted, virtual image of the real image formed by the objective lens.

 Light from a distant object refracts twice in a refracting telescope to create a large virtual image.

 Most large telescopes today are reflecting telescopes.  A reflecting telescope uses a concave mirror, a plane mirror, and a convex lens to collect and focus light from distant objects.

 Light from a distant objects enters one end of the telescope and strikes a concave mirror at the opposite end.  The light reflects off of this mirror and converges. Before it converges at the focal point, the light hits a plane mirror that is placed at an angle within the telescope tube.

 The light is reflected from the plane mirror toward the telescope’s eyepiece.  The light rays converge on a focal point, creating a real image of the distant object.  Just as in a refracting telescope, a convex lens in the eyepiece then magnifies this image.

 The view from telescopes on Earth is different from the view from telescopes in space.  Telescopes on Earth can form blurry images of objects in space due to the Earth’s atmosphere.  The Hubble Space Telescope is above Earth’s atmosphere and forms clearer images of objects in space.

 Imagine being at the bottom of a pool and trying to read a sign by the pool’s edge. The water in the pool would distort the image.  The Earth’s atmosphere blurs objects in space, which is why NASA built the Hubble Space Telescope to be placed into space high above the Earth’s atmosphere.

 The Hubble Telescope is a type of reflecting telescope that used two mirrors to collect and focus light to form an image.

 Most binoculars are like two side-by-side refracting telescopes except that each side also contains two prisms.

 Would you use a telescope to study the cells in a butterfly wing or to tell the difference between an animal or a human hair?  Nah. You’d need a microscope to look at such small objects.

 A microscope uses two convex lenses with relatively short focal lengths to magnify small, close objects.  A microscope, like a telescope, has an objective lens and an eyepiece lens, but they are designed differently.

 Imagine looking at a beautiful sunset. With a click of a button, you can capture it on film.  How does a camera make a reduced image of a life-sized shape on film?

 A camera works by gathering and bending light with a lens. This lens then projects an image onto light-sensitive film to record a scene.

 When you take a picture with a camera, a shutter opens to allow light to enter the camera for a specific amount of time.  The light reflected off the object enters the camera through an opening called the aperture.  It passes through the camera lens, which focuses the image on the film.  The image is real, inverted and smaller than the actual object.

 If we can get ahold of a paper towel roll cardboard tube with a 3 cm diameter and one with a 4cm diameter, we can make a telescope with the lenses we have in class.