Structure and Function Telescopes Structure and Function

Quick Review of Telescope History Hans Lippershey - invented the refractor telescope in 1608 Galileo - the first to use a telescope in astronomy. Galileo's designs used a combination of convex and concave lenses. Kepler - improved the design to have two convex lenses, which made the image upside-down. Kepler's design is still the major design of refractors today, with a few later improvements in the lenses and the glass to make them. Isaac Newton - saw that refractors had a problem with chromatic aberration and developed the reflector telescope which used a primary mirror, rather than a primary lens

Your eyes, and what they see. In order for your eyes to perceive that they are seeing something, a certain amount of photons (light particles) must be detected. If an object is too far away and/or doesn’t emit enough photons your eyes won’t detect it. This can be corrected by bending the light with lenses.

Lenses The lens in your eye works like a glass lens. The light bends as it goes through the different medium (from air through your lens to your retina). Light rays are bent when they intersect glass; a curved surface can produce an image. In your eye, the image is then focused at the retina.

How does this apply to telescopes? The bigger the eye, the more light it can collect. Think about nocturnal animals- they generally have larger eyes for this reason. Their larger eyes gather more light allowing them to see in the dark of night. In a telescope, two pieces make this possible: the objective lens (refractor telescopes) or primary mirror (reflecting telescopes) the eye piece

Parts of the Telescope The objective lens (in refractors) or primary mirror (in reflectors) collects lots of light from a distant object and brings that light, or image, to a point or focus. An eyepiece lens takes the bright light from the focus of the objective lens or primary mirror and "spreads it out" (magnifies it) to take up a large portion of the retina. -This is the same principle that a magnifying glass (lens) uses; it takes a small image on the paper and spreads it out over the retina of your eye so that it looks big.

Eyepiece The purposes of the eyepiece are to: produce and allow you to change the telescope's magnification produce a sharp image provide comfortable eye relief (the distance between your eye and the eyepiece when the image is in focus) determine the telescope's field of view: apparent - how much of the sky, in degrees, is seen edge-to-edge through the eyepiece alone (specified on the eyepiece) true or real - how much of the sky can be seen when that eyepiece is placed in the telescope (true field = apparent field/magnification)

Diagram of a simple telescope Diagram of a simple telescope. Parallel light rays enter from the left, pass through the objective lens, come to a focus at the focal plane, and exit through the eyepiece lens. The focal length of the objective is F, and the focal length of the eyepiece is f. www.ifa.hawaii.edu

When you combine the objective lens or primary mirror with the eyepiece, you have a telescope. Again, the basic idea is to collect lots of light to form a bright image inside the telescope, and then use something like a magnifying glass to magnify (enlarge) that bright image so that it takes up a lot of space on your retina.

The Aperture A telescope's ability to collect light is directly related to the diameter of the lens or mirror -- the aperture -- that is used to gather light. Generally, the larger the aperture, the more light the telescope collects and brings to focus, and the brighter the final image.

Magnification The telescope's magnification, its ability to enlarge an image, depends on the combination of lenses used. The eyepiece performs the magnification. Since any magnification can be achieved by almost any telescope by using different eyepieces, aperture is a more important feature than magnification

There are 2 main types of Telescopes Refractor telescopes, which use glass lenses Reflector telescopes, which use mirrors instead of lenses. Both types accomplish exactly the same thing, but in completely different ways.

Refractor Telescopes Refractors are the type of telescope that most of us are familiar with. They have the following parts: a long tube, made of metal, plastic, or wood a glass combination lens at the front end (objective lens) a second glass combination lens (eyepiece) Refracting telescopes focus light rays by using diffraction, which is the bending of light rays, with glass lenses.

                                                                                                                                                                                                                                                 This is the simplest telescope design you could have. A big lens gathers the light and directs it to a focal point and a small lens brings the image to your eye.

Reflecting Telescopes First developed by Isaac Newton to combat chromatic aberration (rainbow glare) Uses two mirrors instead of lenses Primary mirror: curved mirror used to gather light into the telescope and reflect it to secondary mirror Secondary mirror: smaller, flat mirror used to reflect the focused image into the eyepiece Con: loses light in transfer which can blur image

Reflecting Telescope

Catadioptric Telescopes Combination of refractor and reflector telescopes (uses both mirror and lens capability) Better option than either refractor or reflector telescopes because of the reduced coma (reflective glare) and chromatic aberration (refractive glare) More expensive than both reflective and refractive telescopes

Visible Spectrum www.yorku.ca/eye/spectrum.gif Many modern day telescopes do not use visible light to collect images. Radio telescopes, x-ray telescopes and infrared (IR) telescopes have become a staple of modern day astronomy, producing some amazing images.

Other types of telescopes Infared Telescopes- they are similar to reflective telescopes Located on high mountaintops so the water particles in the lower atmosphere do not impact the quality of the picture taken X-Ray Telescopes- Radio Telescopes-

Very Large Array (VLA) radio telescopes

Hubble Space Telescope space optical telescope Hubblesite.org

Hubble Space Telescope Launched by the US in 1990 Located in low orbit over the atmosphere of the Earth Information from the telescope has been used for over 15,000 research papers

Chandra X-ray Observatory space x-ray telescope