What makes a telescope work

A lens, just like in eyeglasses, bends light passing through it. In eyeglasses, this makes things less blurry. In a telescope, it makes faraway things seem closer. A simple refracting telescope uses lenses to make images bigger and more visible. People with especially poor eyesight need thick lenses in their glasses. Big, thick lenses are more powerful. The same is true for telescopes. If you want to see far away, you need a big powerful lens.

Unfortunately, a big lens is very heavy. Heavy lenses are hard to make and difficult to hold in the right place. Also, as they get thicker the glass stops more of the light passing through them. Because the light is passing through the lens, the surface of the lens has to be extremely smooth. Any flaws in the lens will change the image. It would be like looking through a dirty window. Unlike a lens, a mirror can be very thin. A bigger mirror does not also have to be thicker.

Light is concentrated by bouncing off of the mirror. So the mirror just has to have the right curved shape. This point is also called the focal point, and its distance is measured in negative units. The earliest telescopes, as well as many amateur telescopes today, use lenses to gather more light than the human eye could collect on its own. They focus the light and make distant objects appear brighter, clearer and magnified. This type of telescope is called a refracting telescope. Most refracting telescopes use two main lenses.

The largest lens is called the objective lens, and the smaller lens used for viewing is called the eyepiece lens. The size of an image produced by a lens is proportional to the focal length of the lens. The longer the focal length, the larger the image. The brightness of an image from a telescope depends partly on how much light is collected by the telescope.

The light-gathering power of a telescope is directly proportional to the area of the objective lens. The larger the lens, the more light the telescope can gather. Doubling the diameter of the lens increases the light gathering power by a factor of 4. Brightness of images also depends on how big an area the image light is spread over. The smaller the area, the brighter the image.

The magnifying power of a telescope is the ratio of an object's angular diameter to its naked eye diameter. This depends on the focal length of both lenses. Magnification might seem like the most important aspect of a telescope, but there are limits to how sharp an image a telescope can produce because of the blurring effects of the Earth's atmosphere. Magnifying a blurred image makes it bigger, but not clearer, so the priority when telescopes are built is to have the greatest light-gathering power possible.

Gathering more light makes brighter images, and brighter images make it easier to see faint details. Galileo is credited with being the first person to use a telescope to make observations of the night sky. Includes some basic activities along with facts on the Hubble Telescope. After completing the simple demonstrations the students will have a better understanding of basic telescope design.

Demonstrate an understanding of telescope design by completing activities with magnifying glasses and mirrors. Apply knowledge of telescope design to the Highland Road Park Observatory telescope.

A general property of a telescope is how will it collect light. Have students complete the following telescope demonstrations. Demonstrating a Refracting telescope: Materials: 2 magnifying glasses it works best of one magnifying diameter is larger than the other , a sheet of paper with words on it.

Hold one magnifying glass the bigger one between you and the paper. The image of the print will look blurry. Place the second magnifying glass between your eye and the first magnifying glass. Move the second glass forward or backward until the print comes into sharp focus. You will notice that the print appears larger and upside down. Light enters the objective lens and then passes through the eyepiece lens before it can be focused.

The image you see is larger and upside down. Demonstrating a Reflecting telescope: Materials: flat mirror, magnifying mirror the kind adults use to shave with , magnifying glass, and flashlight.

Place the magnifying mirror on a table to reflect the simulated sun flashlight. Adjust the mirror so that it stands at an angle to the window so that the reflected light is visible against the window or the wall next to it. Prop up the flat mirror between the magnifying mirror and the window or wall, in the path of the reflected light.