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frontpage. Click here to start. Telescopes. By Mehdi Moussali and É lie Chamai. É cole La Dauversi è re, Montreal, June 2000. Content validation and linguistic revision: St é phane Lamarche  Science anim é e, 2000. Translated from French by Nigel Ward. menu. Menu.

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  1. frontpage Click here to start Telescopes By Mehdi Moussali and Élie Chamai École La Dauversière, Montreal, June 2000 Content validation and linguistic revision: Stéphane Lamarche Science animée, 2000 Translated from French by Nigel Ward

  2. menu Menu Optical and mechanical properties of a telescope Introduction to the telescope Functioning of the telescope Apparentmagnitude of stars Giant telescopes The inventors References Concave mirrors

  3. intro The telescope Since its invention by top scientists, the telescope has changed our way of looking at space. Menu

  4. inventors The invention of the telescope was done by several people including: an Italian astronomer en 1616 Niccolo Zucchi Then, a Frenchman in 1630 Marin Mersenne Then, in 1663 an Englishman James Gregory Click here to continue

  5. newton Isaac Newton In 1643 Birth: In 1727 Death: English Nationality: year of the construction of his telescope : 1671 After the other inventors, Isaac Newton was the first to construct a telescope with a spherical metal mirror . Menu

  6. Concave mirrors Functioning of concave mirrors concave mirror Convergence of the light rays towards the focus. focus Menu

  7. newtonian Functioning of the Newtonian telescope secondary mirror (plane) primary mirror (concave) Light Menu

  8. cassegrain An alternative to the Newtonian telescope (left) is the Cassegrain telescope (right) light light Secondary mirror Secondary mirror focus primary mirror primary mirror focus

  9. Optical tube 1 A Newtonian optical tube is composed of the following elements: the barillet ??? This support makes it possible to support the principal mirror securely at the bottom of the tube and to orient it. mirrors

  10. Optical tube 2 The tube The interior of the tube is covered by mat black paint which strongly limits the unwanted reflection of light. The ‘spider’ supports the secondary mirror. the eyepiece holder

  11. Optical tube 3 The eyepiece The amount of magnification depends on the eyepiece. To know the magnification which an eyepiece will give, you must know the focal length of the primary mirror. The magnification can then be calculated for each eyepiece using the following formula: M= F/f where M is the magnification, F the focal length of the primary mirror, and f is the focal length of the eyepiece Mechanics

  12. mechanics Mechanics The axis of declination makes the tube pivot. The fork supports the axis of declination. The axis of right ascension Menu

  13. Giant telescopes GIANT telescopes ESO (European Southern Observatory) has constructed 4 giant telescopes in the north of Chile. This image represents one of the telescopes. The mirror of the instrument weighs 23 tonnes, so imagine how large it must be! Click

  14. woaw WOAW!!! Here is an image made by one of these telescopes. They are among the most precise and clear telescopes in the world. Menu

  15. Seeing stars Seeing stars Scientifically, the brightness of a star, as seen from earth, is called its ‘apparent magnitude’. We use a system developed by the ancient Greeks in which the brightest stars are said to be of first magnitude (magnitude 1) and the dimmest stars visible to the naked eye in ideal conditions are said to be of the sixth magnitude (magnitude 6). This means that the bigger the magnitude number, the dimmer the star. There are about 2500 stars with magnitudes 1 to 6 so that is the number of stars you can see in ideal conditions. If you live in a city then there is likely to be a lot of light pollution and you may be able to see only stars of magnitude 4 or brighter – that means only about 250 stars. The dimmest magnitude you can see in real conditions is called the ‘limiting magnitude’. Graphic

  16. Magnitude gain Magnitude gain Telescopes make stars appear brighter since they gather a lot more light than the tiny pupil of our eye is able to do without help. For example, a telescope with a mirror of diameter 250 mm increases the brightness by 8 magnitudes so that at a location where the limiting magnitude is 6 (meaning that magnitude 6 stars are just visible to the naked eye) then the 250 mm telescope would allow us to see stars of magnitude 14 (6+8 = 14). In other words the limiting magnitude without the telescope is 6 and with the telescope is 14. Here is the formula for the magnitude gain of the telescope in terms of the mirror diameter Dm and the diameter of the pupil of your eye Dp (typically about 6.5mm): magnitude gain = 5 * Log10 (Dm/Dp). Graphic

  17. graph Limiting magnitude as a function of the diameter of the mirror. Menu Mirror diameter (mm)

  18. references rences Refe Books Gagnon, Roger. Construction d’un télescope amateur, Montréal, Conseil de la jeunesse, 1977, 60 pages. Gagnon, Roger. La fabrication d’un miroir de télescope, Montréal, Conseil de la jeunesse, 1977, 67 pages. Menu

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