The telescope is an instrument which increases our ability to observe far away objects through the collection of electromagnetic radiation, the most prevalent type of telescope is the optical telescope which collects light, however there are other kinds of telescopes which collect UV and X -Rays. Optical telescopes use lenses to redirect light to a specified point. Different lenses are used for different magnifications of celestial objects. This essay will be mainly discussing optical telescopes. As we go through the history of optical telescope we can see that there are a few concepts that are fundamental to all the different types of optical telescopes, from the reflecting to the refracting to the hybrid of the two these are as follows. The lens and its properties were known prior to the invention of the optical telescope with simple lenses made from rock crystal being found before recorded history (George & Yannis, 1987). The properties of light such as reflection, refraction and colour were discussed by Ptolemy in his work ‘Optics’ written in the 2nd century (Salih, Al Amri, & El Gomati, 2005) and by the 12th Century ‘reading lenses’, the predecessors to the magnifying glasses, were in use by people suffering from sight deficits (White, 1961). All telescopes have a hole or opening through which light travels called the aperture. This relates to the telescope’s ability to collect light through a lens or mirror, with the bigger the aperture the more light it is able to collect and bring to focus, and the brighter the final image. The focal length of a telescope is the distance required by the objective lens or primary mirror to bring all the light it has collected to a single point (focal point). As a general rule of thumb, the longer the focal length of a telescope the more capable of the telescope to deliver higher magnifications. Finally, the resolution of a telescope is the ability to see fine details in an image, it also moderates the effectiveness of its ability to separate, or resolve, two close object. Resolution depends on the aperture of the telescope, the observing conditions and the quality of the optics. From these developments spectacle makers named, Hans Lippershey, Sacharia Jansen and Jacob Metius, are often credited with the invention of the telescope. Hans was the first known person to apply for a patent on the invention in October 1608 as well as distributing designs for the first practical telescope. However there is much speculation that these people was not the first to make the telescope, nevertheless they were the leading people in making the instrument widely known(King, 2003) Refracting telescopes As Lippershey brought news about this new gadget to light, the story about this instrument spread throughout Europe, including to Galileo Galilei who heard about the telescope whilst at Padua. After working out the basic principles behind how the telescope operates, Galileo manufactured his own eight power telescope. As Galileo began to refine his method of making telescopes (e.g. the way in which he grinded the lenses) he gradually improved the power of the telescopes and used them for observing the sky. Through the use of the telescope Galileo was able to provide key evidence which supported the Sun-Centred / Copernican model of the solar system which contradicted the Ptolemaic, Earth Centred model and thus settled one of the largest debates at the time. Furthermore Galileo found the 4 moons of Jupiter as well as the different phases of Venus, mountains on the moon and discovering that the Milky Way containing many stars. This showed how critical the practical use of the telescope is in the growing field of astronomy. The telescopes which Galileo created are known as refracting telescopes. These telescopes work like a magnifying glass in that it uses a primary concave lens where the light enters telescope.
LIGHT EMITTING DIODES Light Emitting Diodes are electronic components that use the flow of electrons to excite materials into emitting photons of light. A diode is a basic electronic component that allows electricity to flow one way only. The discovery of "light emitting" diodes we believe was an accident sometime around 1907 when a diode in an early radio transmitter was noticed to glow when in use. Incandescent bulbs use resistance in a filament to impede the flow of electricity, heating up to a degree which emits light. It takes high amounts of energy to do this and the filament burns out in time and high levels of wasted energy are given off in the form of heat. Quite a "green" product from a manufacturing and chemical/recyclable point of view. CFL "energy savers", fluorescent tubes and many other conventional lamps use higher frequency alternating current to excite harmful chemicals to emit light. One 5 foot 1,5meter tube contains enough mercury to contaminate a swimming pool. Billions have been dumped into waste disposal. Heavy metal poisons have a cumulative effect. In the long term these cannot be a "fix" for the energy crisis we face today. They are poisoning our earth and also us directly through the food chain and locally with emission of harmful UV. So "Energy savers" are in the writers opinion very dangerous and should be banned. Aquifers for example may soon be or may already have been rendered unusable. Cape Town for example has water shortages in summer, but our municipal uncontrolled dumps are sitting on top of these aquifers. With poison being cumulative up the food chain, we worry about the safety of this water. A lot of our vegetables are grown in this area, using this aquifer water. Has this water or these vegetables been tested? LED lighting uses less energy than most other lighting sources, with current commercially available product generation producing 90 or more lumens per watt and doing so with a good power factor.
A Semiconductor is a solid material that has electrical conductivity in between a conductor and an insulator. Semiconductors are important in electronic technology. The electronic components made of semiconductor materials, are essential in modern consumer electronics such as computers, mobile phones and digital audio players. Silicon is used to create most semiconductors commercially. Semiconductor devices are electronic components that exploit the electronic properties, of semiconductor materials, principally silicon, germanium, gallium, a reside. Semiconductor devices have replaced thermionic devices (vacuum tubes) in most applications. They use electronic conductor in the solid state as opposed to the gaseous state in a high vacuum. Semiconductor devices are manufactured both as single discrete devices and as integrated circuits (ICS). By far silicon (SI) is the most widely used material in semiconductor devices. Its combination of low raw material cost, relatively simple processing and a useful temperature range make it currently the best among the various competition materials. Uses of Semiconductor (i) In manufacturing of electronic goods, e.g- computers, mobile phones, digital audio players. (ii) Also used in digital circuits like microprocessors. (iii) Also used in power semiconductor devices intended for high current or high voltage applications. This is also used in smart power devices.