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Infrared (IR) Radiation: Viewing the Invisible Avi M. Mandell NASA Goddard

Infrared (IR) Radiation: Viewing the Invisible Avi M. Mandell NASA Goddard. Photo by Michi Lauke. Infrared radiation is radiation with a wavelength slightly longer than the reddest visible light

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Infrared (IR) Radiation: Viewing the Invisible Avi M. Mandell NASA Goddard

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  1. Infrared (IR) Radiation: Viewing the Invisible Avi M. Mandell NASA Goddard Photo by Michi Lauke

  2. Infrared radiation is radiation with a wavelength slightly longer than the reddest visible light Infrared radiation is emitted by the same objects that emit visible light (stars, light bulbs, etc), but IR radiation is also emitted by much cooler objects that emit very little or no radiation at visible wavelengths Introduction: What is Infrared Light?

  3. First identified as a type of radiation similar to visible light by William Herschel in 1800 By separating colors with a prism and measuring their temperatures, he noticed that temperatures went up in a region outside the visible colors Discovery of Infrared Radiation

  4. For any object cooler than 3500 K, the intensity of the IR light released is greater than that of the visible light Relation Between IR and Visible Light Visible Infrared • An object with a certain temperature emits light across the whole spectrum (called “blackbody” radiation)

  5. Relation Between IR and Visible Light • Even when an object is much cooler than 3500 K, it can be observed in visible wavelengths through reflected light

  6. Relation Between IR and Visible Light Visible IR • The reflective properties of material depend on porosity compared with the wavelength of radiation • * Rule of thumb: the maximum wavelength of reflected light is equal to the size of the particle/hole

  7. Infrared Spectrum • The intensity of light as a function of wavelength, called the “spectrum”, can tell you a great deal about an object • You can measure the temperature by looking for the blackbody curve • You can identify atoms and molecules by their absorption • Many molecules only absorb in the IR Solar Radiation: Above and Below the Atmosphere

  8. Infrared Spectrum • Due to the dust and molecules in the Earth’s atmosphere, it is very opaque at most wavelengths: UV (from ozone), much of IR and mm wavelengths (water, CO2, methane), and wavelengths longer than 10 meters

  9. What Can We Learn from Infrared Observations? NIR MIR FIR • Infrared radiation can peer through dust, as well as illuminate it • Combining IR with other wavelengths provides a rough measurement of temperature

  10. What Can We Learn from Infrared Observations? • Targeting infrared light allows us to see cool, dim objects (like planets) near bright, hotter ones (like stars) • The light from the star is much dimmer in the IR because the blackbody spectrum drops off quickly • We can detect the light from the planet as it passes behind the star

  11. Questions?

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