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By Mehdi Moussali and Élie ChamaiBy Mehdi Moussali and Élie Chamai
École La Dauversière, Montreal, June 2000École La Dauversière, Montreal, June 2000
Content validation and linguistic revision: Stéphane Lamarche
Science animée, 2000
Content validation and linguistic revision: Stéphane Lamarche
Science animée, 2000
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Translated from French by Nigel WardTranslated from French by Nigel Ward
Introduction to Introduction to the telescopethe telescope
Optical and Optical and mechanical mechanical
properties of a properties of a telescopetelescope
Functioning of Functioning of the telescopethe telescope
ApparentApparent magnitude of magnitude of stastarsrs
GGianiant t telescopestelescopes The inventors The inventors
References References Concave Concave mirrorsmirrors
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Since its invention by top scientists, the telescope has changed our way of looking at space.
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The invention of the telescope was done by several people including:The invention of the telescope was done by several people including:
an Italian astronomer en 1616 Niccolo Zucchi
Then, a Frenchman in 1630Marin Mersenne
Then, in 1663 an Englishman
James Gregory
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inventors
Birth:
Nationality:
year of the construction of his telescope :
Death:
English
After the other inventors, Isaac Newton was the first to construct a telescope with a spherical metal mirror .
After the other inventors, Isaac Newton was the first to construct a telescope with a spherical metal mirror . Menu
newton
concave mirror
focus
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Convergence of the light rays towards the focus.
Concave mirrors
primary mirror (concave)
secondary mirror (plane)
Light
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newtonian
Secondary mirror
primary mirror
Secondary mirror
primary mirrorfocus
focus
An alternative to the Newtonian telescope (left) is the Cassegrain telescope (right)
light light
cassegrain
A Newtonian optical tube is composed of the following elements:
mirrors the barillet ???This support makes it
possible to support the principal mirror
securely at the bottom of the tube and to
orient it.
Optical tube 1
The ‘spider’ supports the secondary mirror.
The tubeThe interior of thetube is covered by
mat black paint which strongly limits
the unwanted reflection of light.
the eyepiece holder
Optical tube 2
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/fwhere M is the magnification,F the focal length of the primary mirror, and f is the focal length of the eyepiece
Mechanics
Optical tube 3
The axis of declination
The fork
The axis of right ascension
makes the tube pivot.supports the
axis of declination.
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mechanics
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!
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Giant telescopes
Here is an image made by one of these telescopes. They are among the most precise and clear telescopes in the world.
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woaw
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
Seeing stars
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
Magnitude gain
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Limiting magnitude as a function of the diameter of the mirror.
Mirror diameter (mm)
graph
BooksBooksGagnon, Roger. Gagnon, Roger. Construction d’un télescope amateurConstruction d’un télescope amateur, ,
Montréal, Conseil de la jeunesse, 1977, 60 pages.Montréal, Conseil de la jeunesse, 1977, 60 pages.
Gagnon, Roger. Gagnon, Roger. La fabrication d’un miroir de télescope,La fabrication d’un miroir de télescope, Montréal, Conseil de la jeunesse, 1977, 67 pages.Montréal, Conseil de la jeunesse, 1977, 67 pages.
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references