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Monday October 29th 2012.docx

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Bozidar Mitrovic

Monday October 29 2012h Astronomy Lecture: Light and telescopes - all information about stars is obtained from the light which they emit using the physical laws - light is just a particular type of electromagnetic wave - wavelength is denoted by greek letter A (lambda) - color wavelength - to express the wavelengths of visible light we use nanometers (nm) : 1 nm = 10*-9m - for visible light 400 nm(violet) < 2<700nm (red) - at the wavelengths longer than 700nm we have o infrared o microwaves o radio waves – some (but not all blocked by our atmosphere) - at wavelengths shorter than 400nm o uv o x-rays o gamma-rays - x-rays and gamma-rays are blocked by the ionosphere (the top part of the earths atmosphere) - the energy of electromagnetic wave is carried in pockets called photons: - the energy of the photon is given by e= constant/2 - thus, the shorter the wavelength the higher is the energy of the photon and vice versa - all stars are so distant that the amount of their light which enters the eye is very small - telescopes are used to collect more light - they are based on o refraction of light  because light propagates at a reduced speed in the Denver medium st Wednesday October 31 , 2012 Refracting telescopes - (so- called refractors) use a lens to collect (gather) light - in this case the objective is a lens - all pass through the same focus (focal point) - it is possible to collect
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