AST 101 Lecture Notes - Lecture 9: Gustav Kirchhoff, Fraunhofer Lines, Visible Spectrum
Document Summary
The earth"s atmosphere is only transparent to the optical and radio part of the spectrum. Thus to observe in other wavelength regimes, we have to launch satellite observatories. As this has become possible with the dawning of the space age, our understanding of the universe has advanced enormously. This is because observations in different wavelength regimes tell us about fundamentally different physical processes and environments. As an example, when we observe in the optical, we are observing starlight. This is emitted by hot, dense gas on the surfaces of stars. We are learning about matter at thousands of kelvin, and at comparatively high density. When we observe in the far ir (50 to. 200 microns), we are observing thermal radiation from dust grains at temperatures of 10 to 20 k. thus, we are studying the conditions of very cold matter in interstellar space.
