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8/9/2019 Module P7 L4
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Before 1609, all
astronomy was done
with the ³naked eye´ ±that is to say, without
telescopes.
The picture shows thefamous astronomer
Tycho Brahe making
observations with his
³mural quadrant´.
(The person ³inside´
the quadrant is just a
picture.)
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Galileo¶s Telescope
In 1609, Galileo Galilei was one of the first people to turn the newly invented
telescopes to the sky.He discovered many things including:
the moons of Jupiter, named the ³Galilean Moons´ in his honour
mountains on the Moon ± before this, people thought it was a perfectly smooth sphere
sunspots ± although he damaged his eyes by staring directly at the Sun through
his telescope.
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The Polish
astronomer Hevelius
built this 20 metrelong telescope in
1673 ± the
magnification was
very large but it wasvery difficult to use.
Light pollution from towns
and cities was not aproblem at that time!
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The Irish astronomer Lord
Rosse drew this picture of the
M51 galaxy in 1825.
The photograph of the same
galaxy was taken by the Hubble
Space Telescope in 2005.
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Telescopes have become bigger over
the years as astronomers try to
gather more light from distant objects.
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The Hubble
Space Telescope
has a smaller aperture than
many Earth
based
telescopes.
However, it is not
affected byweather, air
pollution or light
pollution.
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How to Build a Telescope
1. You need a lens with a long focal lengthto be the objective lens which gathers
the light.
2. You need a lens with a short focal lengthto be the eyepiece lens which helps to
produce a real, magnified and inverted
image.
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Objective Eyepiece
Focal length of
objective lens
Focal length of
eyepiece lens
1º 9º
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Magnification
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Example: The objective lens of a telescope has a focal length of 1.2 m and its
eyepiece has a focal length of 0.10 m.a) Calculate the magnification.
b) A galaxy has an angular size of 0.2º. What is its angular size when viewed
through this telescope?
120.10
1.2 ionmagni icat !!
a)
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Magnification
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Example: The objective lens of a telescope has a focal length of 1.2 m and its
eyepiece has a focal length of 0.10 m.a) Calculate the magnification.
b) A galaxy has an angular size of 0.2º. What is its angular size when viewed
through this telescope?
Angular size = 12 x 0.2 = 2.4 ºb)
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Magnification
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