Electromagnetic Radiation and Scientific Instruments. PTYS April 1, 2008

Transcription

1 Electromagnetic Radiation and Scientific Instruments PTYS April 1, 2008

2 Announcements Deep Impact 6 PM Wednesday Night Pizza, no beer Watch at home if you can t watch here. It will be discussed in class on Thursday New homework posted today

3 The Cassini Spacecraft

4 Scientific Instruments Radiation Fields and Particles Cameras Spectrometers (UV, Vis, IR) Radar Radio Laser altimeters Mass spectrometers Magnetometers (measures magnetic fields) Langmuir probes (measures electrical currents) Energetic particle detectors

5 CCD Cameras, from Astronomers to you Close-up of a CCD chip The array of CCDs used on the Sloan Digital Sky Survey Something bought in Walmart

6 How CCDs Work The image area is divided up into an array of very small (10µm x 10µm) individual detectors called pixels. How It Works: The Charged-Coupled Device, or CCD by Courtney Peterson, Journal of Young Investigators

7 Filters Separate light into wavelengths The set of filters used on the Hubble Space Telescope Camera Optical (Interference) Filters

8 Cassini Camera Imaging Science Subsystem (ISS) Narrow Angle Camera (NAC) Mechanical Diagram Actual Photo - basically a 10 cm focal length telescope

9 Remember the Electromagnetic Spectrum

10 Two Kinds of Light All warm bodies emit radiation. We can characterize the radiation from objects as reflected or emitted. Reflected radiation is light that is produced by a another object (usually the Sun) that then bounces off the object being studied. Emitted radiation is produced by the object itself, as a consequence of its temperature. Usually, UV and visible light are reflected radiation and IR light is emitted radiation.

11 Spectrum: 1 a band of colors, as seen in a rainbow, produced by separation of the components of light by their different degrees of refraction according to wavelength. the entire range of wavelengths of electromagnetic radiation. An image or distribution of components of any electromagnetic radiation arranged in a progressive series according to wavelength. A similar image or distribution of components of sound, particles, etc., arranged according to such characteristics as frequency, charge, and energy. 2 used to classify something, or suggest that it can be classified, in terms of its position on a scale between two extreme or opposite points : the left or the right of the political spectrum. a wide range : self-help books are covering a broader and broader spectrum.

12 The First Spectrometer was a Prism

13 Spectrometers Breaks light into the contributions from various wavelengths. This is what scientists call a spectrum.

14 Stefan-Boltzmann Law All objects emit electromagnetic radiation. The power radiated by an object at temperature T is proportional to the temperature to the 4th power. P = "#T 4 P is the power radiated σ= W m -2 K -4 is the Stefan-Boltzmann constant ε is the emissivity, usually equal to ~1.

15 Wein s Law: λ= 0.003/T The temperature of an object determines the spectrum of its emitted radiation. High temperatures imply short wavelengths; low temperatures imply long wavelengths. The wavelength at which most of the radiation is emitted is inversely proportional to the temperature. The lava from this volcano glows because it is hot. Wein s Law λ = 0.003/T λ is the wavelength in meters T is the temperature in Kelvins

16 Spectrum of Thermal Radiation The peak of the curve is determined by Wein s law. The spectrum of radiation from warm bodies has a characteristic shape. The area under the curve is determined by the Stefan-Boltzmann law.

17 Spectrum Variations with Temperature

18 The Sun emits visible light. The Sun s surface temperature is 6000K. Thus it emits radiation at a wavelength of λ= 0.003/6000 meters λ= meters This is in the middle of the visible spectrum The Spectrum of the Sun.

19 Earth emits IR radiation Earth s temperature is 300K, and thus radiates at a peak wavelength of λ = / 300 meters, λ = 10x10-6 meters. This is in the infrared region of the spectrum.

20 Spectra Identify Materials Emission features Absorption features

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22 Spectral Features from Titan Emitted Light At ultraviolet wavelengths we see emissions characteristic of nitrogen and hydrogen At visible and near infrared wavelengths we see absorption features due to methane. Methane = CH 4 = swamp gas Reflected Light

23 Thermal Emissions from Titan identify numerous molecules Wavelength