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October 17, 2011 – 10am Class. Today: Infrared Camera, get handout Finish writeup and turn in, on Friday On-line quiz due Friday HW on Fractals due Friday. LIGHT and Telescopes. IR Light. The 10 micron camera contains a detector which is sensitive to infrared (IR) light.

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october 17 2011 10am class

October 17, 2011 – 10am Class

Today: Infrared Camera, get handout

Finish writeup and turn in, on Friday

On-line quiz due Friday

HW on Fractals due Friday

ir light
IR Light

The 10 micron camera contains a detector which is sensitive to infrared (IR) light.

All objects radiate "black body" radiation, or "Planck radiation", by virtue of their temperature.

slide7

For objects near room temperature the radiation peaks in the infrared. Your eyes, which are sensitive to optical light, cannot see this radiation unless the object is VERY hot.

  • The visible or optical light you see is reflected optical light from the sun or lamps.
  • Hotter things are brighter in the IR camera than cooler things.
  • Some materials are opaque to IR light, but transparent to visible light.
  • Some materials are transparent to IR light, but opaque to visible light.
  • IR light can be reflected by a mirror, just like optical light.

Optical light requires a much smoother surface on mirrors than IR light because optical light has shorter wavelength than IR

everyday uses of ir light
Everyday Uses of IR light
  • One everyday use of IR light is in remote control devices
  • IR cameras are used on ships and in buildings to look for hot spots in electrical wiring
  • night-time spotting of people (who are warmer than their surroundings)
  • for seeing "through" smoke in a fire
    • http://www.youtube.com/watch?NR=1&v=Oj22mr_A20U
astronomers use ir light
Astronomers use IR light

(1) To measure temperatures; (2) to look "through" dust

Optical or Visible Wavelengths

IR wavelengths

The Trapezium in Orion: Stars are forming out of gas and dust

slide11

Consider a hot, low density glob of hydrogen gas.

λ = 656.3 nm (3→2)

λ = 486.1 nm (4→2)

λ = 434.0 nm (5→2)

Light is emitted with wavelengths or frequencies corresponding to energy jumps between electron orbits.

slide12

1) Hot, low density gas produces an emission line spectrum.

5→2

4→2

3→2

Spectrum of hydrogen at visible wavelengths.

slide13

Carina Nebula: a cloud of hot, low density gas about 7000 light-years away.

Its reddish color comes from the 656.3 nm emission line of hydrogen.

slide14

A cool, low density glob of hydrogen gas in front of a light source.

Light is absorbed at specific wavelengths corresponding to energy jumps between electron orbits.

slide15

2) Cool, low density gas produces an absorption line spectrum.

5←2

4←2

3←2

Spectrum of hydrogen at visible wavelengths.

slide17

Hydrogen line at 656.3 nm

The spectrum of the Carina Nebula:

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