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Astronomy for beginners Telescopes By Aashman Vyas What are Telescopes? A telescope is an instrument designed for the observation of remote objects by the collection of Light A telescope’s diameter is measured in inches, meters or centimeters Eg: A 6inch Telescope is bigger than a 4inch Telescope because it can collect more light How do Telescopes Work? Telescopes work by using a system of mirrors and lenses to refract, magnify or bend light They can be used for terrestrial viewing and deep-space viewing The main purpose of the Telescope is that they make far away objects seem more closer Telescopic Words Aperture: Aperture is the size of the main optical lens of the Telescope Counter weight: The thing that keeps the Telescope Balanced on it’s Tripod CCD Camera: A CCD Camera converts optical brightness into electrical Signals that are sent to a Computer. (Otherwise known as a Telescope image/video Camera) Lens: An Eyepiece attached to a Telescope that lets you see stuff. Magnitude: Magnitude of a celestial body is a measure of its brightness as seen by an observer on Earth Observatory: A type of domed house housing a large Telescope Electromagnetic Spectrum: The Spectrum of Light with all the other wavelengths Types of Telescopes There are many types of Telescopes Refractor Newtonian Reflector Schmidt-Cassegrain (falls under Catadioptric category) Refractor Telescope The Refractor, is a telescope that uses lenses to refract, (bend), the light that it collects This refraction causes parallel light rays that converge at a focal point at the opposite end, where they can be magnified by an eyepiece The large lens at the front is called the objective lens. The objective lens is usually composed of two or more individual lenses that are bonded and or arranged together to make up what is called the objective lens cell The glass material used can also vary which will help in the overall performance of the objective lens Refractor Telescope Advantages and Disadvantages Advantages -Little or no maintenance and is easy to use -Reliable due to the simplicity of design -Good for terrestrial viewing -Objective lens is usually permanently mounted and aligned -Sealed optical tube reduces image degrading air currents and protects the optics Disadvantages -Usually more expensive per inch of aperture than Newtonians or Catadioptrics -Heavier, longer and bulkier than equivalent aperture Newtonians or Catadioptrics -Less suited for observation of deep sky objects such as distant galaxies and nebulae because of practical aperture limitations Newtonian Reflector The Newtonian Reflector, is a telescope which uses a spherical or concave parabolic primary mirror to collect, reflect and focus the light onto a flat secondary mirror This secondary mirror in turn reflects the light out of an opening in the side of the tube and into an eyepiece for focus and magnification Newtonian Reflector Advantages and Disadvantages Advantages -Excellent for faint deep sky objects such as remote galaxies, nebulae and star clusters due to the generally fast focal ratios -Reasonably compact and portable up to focal lengths of 1000mm -Low in optical abnormalities and deliver very bright images Disadvantages -Requires regular alignment (collimation) of optics in order to perform at its best. Badly aligned optics can make the image quality suffer quite dramatically. -The open nature of the tube assembly could mean more complicated cleaning of mirror surfaces when compared to telescopes of other designs -Generally not suited for terrestrial applications -Slight light loss due to secondary (diagonal) obstruction when compared with refractors Schmidt-Cassegrain In Schmidt Cassegrain designs the light enters a thin aspheric Schmidt correcting lens The light then strikes the primary mirror and is reflected back up to the secondary mirror that reflects the light out an opening in the rear of the instrument Schmidt's usually have shorter focal lengths thus making them more suitable for fainter deep sky objects The thinner corrector plate means the Schmidt is faster to reach thermal stability Schmidt-Cassegrain Advantages and Disadvantages Advantages -Best all-around, all-purpose telescope design. Combines the optical advantages of both lenses and mirrors while canceling their disadvantages -Excellent for deep sky observing or astrophotography with fast films or CCD's -Very good for lunar, planetary and binary star observing or photography Disadvantages -More expensive than Newtonians of equal aperture -It is not what people expect a telescope to look like -May suffer from image shift when focusing due to focus design moving the entire primary mirror Bibliography The big book of Stars and Planets by Robin Kerrod Google Images www.aoe.com.au/telescope_types.html Ask an Astronomer.com Bluebird Book’s Tell me how Thank You For Watching!!!