Astro 120 Chapter 6.docx - Astro 120 Chapter 6: Telescopes:...

This preview shows page 1 - 3 out of 8 pages.

Astro 120Chapter 6: Telescopes: Portal of Discovery6.1 Eyes and Cameras: Everyday Light Sensors:Eyes + cameras work similarly:-Eyes:oPupilControls how much light enters the eyeDilates (open wider) in low light and constricts in brightlightoLensBends light to form an image on the retinaoRetinaContains light-sensitive cells (cones or rods)that, when triggered bylight, sends signals to the brain via the optic nerve.Bending Light:-Earth’s atmosphere also bends lightoSun looks squashed at sunset becauseLight from lower portion of the sun passes through more atmosphereBends slightly more than light from upper portion-Parallel lines bends to afocal point-Not parallel lines don’t converge at the focusoBending to form animagePlace where image appears in focus is calledfocal planeRecording images:-Camera:oSmall opening for light to enteroCamera lens – bends the light and bringing it to a focus on a detectors thatmakes a permanent record of the imageoShutter – analogous to an eyelidLight can reach the detector only when the shutter is openUsed to control exposure time of an imageAmount of time during which light collects on the detectoroLong exposure = more light reaches detector whichallows detector to reach details that might be too faintto be seen in shorter exposuresoModern detectors – electronic chips that physically divide into grids of pictureelements/pixelsPhoton of light strikes a pixel – electric charge to accumulateImage Processing
6.2 Telescopes: Giant Eyes:Two most important properties of a telescope:-Light-collecting areaoHow much light it can collect at one timeoTelescopes are generally roundCharacterize size by the diameter of its light collecting areaoRelatively small increase in diameter = big increase in light collecting area-Angular resolutionoSmallest angle over which we can tell that two dots/two stars are distinctoHuman eye = angular resolution of about 1 arcminuteTwo scars can appear distinct only if they have at least this muchangular separation in the skyoAngular separation between two points of light depends onBoth actual separation and distance from usInterference limits a telescope’s angular resolution as beams of lightcaninterferewith one anotherDiffraction Limit– angular resolution that a telescope couldachieve if it were limited only by the interference of lightwavesoBetter angular resolution for larger telescopes = smallerdiffraction limitTwo basic designs of telescopes:-Refracting telescopeoTelescope that uses transparent glass lenses to collect and focus lightoEarliest telescopes-Reflecting telescopeoUses precisely curvedprimary mirrorto gather lightmirror reflects the gathered light to asecondary mirrorthat lies in

Upload your study docs or become a

Course Hero member to access this document

Upload your study docs or become a

Course Hero member to access this document

End of preview. Want to read all 8 pages?

Upload your study docs or become a

Course Hero member to access this document

Term
Fall
Professor
N/A

  • Left Quote Icon

    Student Picture

  • Left Quote Icon

    Student Picture

  • Left Quote Icon

    Student Picture