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Chapter 6

CHAPTER 6 ASTRO.docx

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Department
Astronomy & Astrophysics
Course Code
AST201H1
Professor
Michael Reid

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CHAPTER 6
TELESCOPES
6.1
Refraction is the bending of a wave
Nowadays, most images are recorded digitally with electronic detectors called charge
coupled devices (CCDs). A CCD is a chip of silicon is chip that is extremely sensitive to
photons. Its physically divided into a grid of squares called picture elements (pixels)
Advantages of CCDs over photographic film: much more sensitive to light; have a much
wider dynamic range which allows it to record dim and bright light at the same time; can
be digitally processed to bring out the details of the image
6.2
2 most important properties of a telescope: light collecting area and angular resolution
a 10m telescope has a light collecting area 25 times greater than a 2m telescope
([10/2]^2 = 25)
angular resolution is the SMALLEST angle over which we can tell two dots or two stars
are distinct (Human angular resolution is 1/60 degrees)
Hubble space telescope (2.4m) has a angular resolution of about 0.05 arcsecond for
visible light
The angular resolution that a telescope could achieve if it were limited only by the
interference of light waves is also called diffraction limit (depends on diameter of
telescope and wavelength of light)
The larger the telescope, the smaller the diffraction limit which leads to a better
(smaller) angular resolution
2 basic designs of telescopes: refracting and reflecting telescope
A refracting telescope uses lenses to collect and focus light
A reflecting telescope uses precisely curved primary mirrors to gather light
Observations through the telescope fall into 3 categories: imaging (photographs),
spectroscopy (study spectra) and timing (changes with time)
Nowadays, most astronauts use invisible light to record images
Spectrographs use diffraction gratings to separate the various colors of light into
spectra, which are then recorded with a detector such as a CCD

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Description
CHAPTER 6 TELESCOPES 61Refraction is the bending of a waveNowadays most images are recorded digitally with electronic detectors called charge coupled devices CCDs A CCD is a chip of silicon is chip that is extremely sensitive to photons Its physically divided into a grid of squares called picture elements pixelsAdvantages of CCDs over photographic film much more sensitive to light have a much wider dynamic range which allows it to record dim and bright light at the same time can be digitally processed to bring out the details of the image 622 most important properties of a telescope light collecting area and angular resolutiona 10m telescope has a light collecting area 25 times greater than a 2m telescope 102225angular resolution is the SMALLEST angle over which we can tell two dots or two stars are distinct Human angular resolution is 160 degreesHubble space telescope 24m has a angular
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