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Dayton PHY 250 - Collecting Electromagnetic Information

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Slide 1Slide 2Slide 3Slide 4Slide 5Slide 6Slide 7Slide 8Slide 9Slide 10Slide 11Slide 12Slide 13Slide 14Slide 15Slide 16Slide 17MethodsEye (visible window)Camera – film Camera – CCD (Digital)Collecting Electromagnetic InformationEye (visible window)Advantages:Everyone wants to see objects directlyDisadvantages:Light gathering capability – can see without telescope down to magnitude 6Image cannot be storedCannot do a time exposureCollecting Electromagnetic InformationCamera – filmDiscussions of film ended in 08/WIDigital cameras have become affordable and high resolutionCollecting Electromagnetic InformationCamera – CCD (Digital)Advantages:ResolutionCan do a time exposureCan store directly to a computerCan be manipulatedShort Exposure TimesDisadvantagesExpense – but not badPixilated ImageCollecting Electromagnetic InformationCollecting Electromagnetic Information – Digital ImagePeter PowersDepartment of Physics6 in Compound TelescopeMotor driveCollecting Electromagnetic Information – Digital ProcessingCollecting Electromagnetic Information – Digital ProcessingRawDuplicate and Blur InvertLayer and FlattenCollecting Electromagnetic Information – Digital ProcessingCollecting Electromagnetic Information – Digital ProcessingComparison – Film vs CCDThe Advantages of CCD ImagingProfessional astronomers have been using CCDs for nearly two decades and have no thoughts about going back to film. The advantages are impressive:* CCD cameras are up to 100 times more sensitive than film * CCD images are digital, meaning no film-processing, scanning, scratching, or fading * CCD cameras have a much greater dynamic range than film, meaning they can more easily capture both faint and bright detail in a single exposure * CCDs are capable of resolving finer detail than film (this can, however, be limited by the telescope used and the atmospheric conditions) For the amateur, several other advantages apply as well:* Taking images with a CCD is generally much easier than with film * Learning goes faster due to the ease-of-use and shorter exposure times * Light pollution is less obtrusive and more easily removed from CCD images, meaning imaging from a backyard site is more likely to be possible with CCDComparison – Film vs CCDEfficiency and ExposureEfficiency* A CCD can record as much as 90% of the incident photons* Film will record less than 5% of the incident photonsCCD will record object 10 to 20 times fainter than film with the same exposure timeExposure Times* CCD can record the same image with less than one tenth of the exposure time for filmAbove: On the left is a CCD image taken from a suburban location. The exposure time is about 30 minutes. On the right is a film image of the same object taken using a similar telescope. The exposure time is over 2 hours and the level of detail is far less than the CCD image. At full resolution the difference is even more impressive.Comparison – Film vs CCDExposurePhotometer – An instrument which measure the brightness of an objectWill measure the TOTAL brightness of an object, which might be difficult to interpret. However, when combined with filters, can be used to measure the amount of light produced over a narrow range of frequencies. This can be compared with standard Blackbody radiation curves to determine the temperature of the objectPhotometryPhotometryPhotometer – An instrument which measure the brightness of an objectWill measure the TOTAL brightness of an object, which might be difficult to interpret. However, when combined with filters, can be used to measure the amount of light produced over a narrow range of frequencies. This can be compared with standard Blackbody radiation curves to determine the temperature of the objectPhotometryXIntensityWavelengthXXPhotometer – An instrument which measure the brightness of an objectWill measure the TOTAL brightness of an object, which might be difficult to interpret. However, when combined with filters, can be used to measure the amount of light produced over a narrow range of frequencies. This can be compared with standard Blackbody radiation curves to determine the temperature of the objectPhotometryXIntensityWavelengthTemperature of object is 7000 KXXSpectroscopes can be used to analyze the image through the eyepiece. The spectra can then be viewed with the eye, a camera, or a CCE for analysis.Spectroscopy


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