Techniques d'observation spectroscopique d'astéroïdes

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Why spectroscopy?
spectrum. By carefully analyzing the spectra it is possible to obtain information about the comtel-00785991,
version 1 - 7 Feb 2013
Much of the knowledge about the Univers came from the study of electromagnetic radiation received from the
cosmic bodies. The most important method to study the electromagnetic radiation is spectroscopy.
This chapter introduces the theory behind the application of spectroscopy in astronomy. A short description
of the basic components of a spectrometer (the prism and gratings) is made. The transparency of the Earth
atmosphere as a function of wavelength is presented. A simple example of the way in which the properties of
celestial bodies could be studied using spectroscopy is shown. The chapter ends by outlining the principles
for applying spectroscopy in asteroid studies.
Spectroscopy is one of the most powerful scientific tools for studying the nature. The study
of celestial bodies using spectroscopy connects astronomy with fundamental physics at atomic
and molecular levels.
The beginning of spectroscopy applied to celestial bodies could be traced back to early
nineteenth century with the discovery of dark lines in the solar spectrum by W. H. Wollaston
in 1802 and J. von Fraunhofer in 1815. Fraunhofer did not know what is the cause for the dark
lines he observed besides the well known characteristic colors of the rainbow. However, he
catalogued the exact wavelength of each dark line and today these are still known as Fraunhofer
lines.
On the contrary, in the same period the positivist French philosopher Auguste Comte noted
referring to celestial bodies: "We will never know how to study by any means the chemical
composition, or their mineralogical structure".
Performing similar observations using light from brightest stars, Fraunhofer concluded that
most of the spectral features are somehow related to the composition of the object he observed
[Tennyson, 2005]. The physical explanation came later, with the development of quantum
mechanics: the dark lines at discrete wavelengths arise from the absorption of energy by the
atoms or the ions in the star atmosphere.
Nowadays, the laboratory spectroscopic studies of different chemical components provide
the basis for interpreting astronomical spectra. There is a direct connection between the physical
parameters of a celestial body and the information that can be obtained by observing its