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Chapter 5

AST101H5 Chapter Notes - Chapter 5: X-Ray, Adaptive Optics, Hubble Space Telescope


Department
Astronomy
Course Code
AST101H5
Professor
John Lester
Chapter
5

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Chapter 5
Telescopes
Telescope Fundamentals
Telescopes enables astronomers to observe things not visible to the naked eye
Light Gathering Power
Telescopes gather much more light than your eye, allowing more stars to
become visible
For your eyes to see an object, photons from it must strike the retina in
large enough numbers to stimulate chemical reactions in nerve cells
How bright an object is depends on the number of its photons that
enter our eye per second, a number limited to the size of our
pupils
Telescopes allow us to collect photons by funneling them into our eyes
The bigger the telescope, the more photons it collects
More photons means brighter image, so a larger telescope may be able
to see stars that a smaller telescope could not detect
Focusing gathered light
Once light has been gathered, it must be focused to form an image or to
concentrate it on a detector
Refractor
A telescope in which light is gathered and focused by a lens
Refracting
The process of the lens of the telescope bending light rays to
focus the light
Disadvantages
Expensive
Sags in the middle, distorting images
Most transparent materials bring different color lights to focus at
different rates, causing chromatic aberration
Reflectors
A telescope where light is reflected off of mirrors towards a focus point
Mirrors are made of glass coated with reflective material
Advantages
Light doesn't pass through the glass, there are no chromatic
aberrations
Because the light doesn’t pass through the mirror, the back of the
mirror can be supported, allowing for larger sizes
Telescopes are mounted to pivots so great care in construction and
design is required to ensure they are able to move with precision
Mirrors deform very slightly when they are moved
To solve this, astronomers used a properly supported thin piece of
glass, as thin pieces were proven to hold their shape better than
thicker pieces
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