AST— Jan 26 Lecture + Chapter Notes

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University of Toronto St. George
Astronomy & Astrophysics
Michael Reid

ASTTelescopes Types of Telescopes Thursday January 26 201261Eyes And Cameras Everyday Light Sensors How does your eye form an image y Eyelens a pupil and a retina y Retina contains light sensitive cells cones and rods when triggered by light send signals to the brain via the optic nerve y Lens creates an image on your retina because it bends lighty Light travels slowly through denser matter than air o Refractionchange in speed causes the wave to bendMakes vision possible y Light rays farther from the center bend more y Parallel rays of light converge to a point called the focus o Distant objects y Rays are ben to form an image of the original objecty Focal planeplace where the image appears in focus of the lens y Pupil controls the amount of light enteringdilates in low light levels ie nightHow do we record images y Detectorany device that records light including photographic film and various types of digital imaging chips y Camera lens plays the role of the lens of the eye and the detector plays the role of the retinay Recorded images are more reliable y Camera can control the exposure timelonger exposure means more photons allowing the detector to record things our eyes cannot see y Most images are recorded digitallyCCDs chargedcouple devices o Chip divided into pixels 62Telescopes Giant Eyes What are the two most important properties of a telescopedetermines how much light it gathers measured in diameters y Light collecting areay Angular resolution determines how much detail we can see in its images o Angular separation between two points of light depends both on their actual separation and on their distance from us y Large telescope have amazing angular resolution smallerie will let you read a book from a km away y Interference limits a telescopes angular resolution o Diffraction limitangular resolution limited only by interference of light waves o Larger telescope has a smaller diffraction limitLarger diffraction limitpoorer angular resolution
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