Introduction to Spectroscopy and Astronomical Observations

Abstract

This chapter presents an introduction to the techniques and tools used in astronomy and astrophysics research, mainly focused on spectroscopy. The basic concepts of spectroscopy are first described, from the Schrödinger equation to the Lambert–Beer’s law. The spectroscopy of solid systems, widely found in astronomical media, is studied in more detail. An introduction is provided also to the basic concepts of astronomical observations, and the information that can be obtained from them, both in the gas phase and in solid systems. An appendix is included with conversion factors for some of the many magnitudes and units employed in this area.

Appendix: Units and Conversion Factors

Several units are used in spectroscopy which are especially suitable for specific spectral regions, or traditionally used by spectroscopists or astrophysicists. Some of them are listed below, where <> means equivalent to, and c = 2.99792458 × 10¹⁰ cm s⁻¹, Avogadro’s number N_A = 6.0221367 × 10²³ molec mol⁻¹, Boltzman’s constant k = 1.38064852 × 10⁻²³ m² kg s⁻² K⁻¹ (1.38064852 × 10⁻¹⁶ erg K⁻¹ in cgs units) and Planck’s constant h = 6.6260755 × 10⁻³⁴ J s:

Frequency ν (microwave region) to wavenumber $\overline{\nu}$: 1 GHz = 10⁹ Hz <> 1/c cm⁻¹= 3.33564 ×10 ⁻² cm⁻¹; 1 kHz = 10³ Hz <> 3.33564 × 10⁻⁸ cm⁻¹.

Wavenumber $\overline{\nu}$ (infrared region) to wavelength λ: mid-IR region: 1000 cm⁻¹ <>10 μm; 3000 cm⁻¹ <> 3.333 μm; near-IR region: 6000 cm⁻¹ <> 1.6 μm.

Wavelength λ (visible and UV regions) to energy E: 1 μm <> (hc/λ) 1.986447 × 10⁻¹⁹ J <> (hcN_A/λ) 11.96266 × 10⁴ J mol⁻¹; 665 nm (approx. red light) <> 17.98899 × 10⁴ J mol⁻¹.

Other energy units (X-ray region): 100 eV <> 9.64853 × 10⁶ J mol⁻¹ <> 1.23984× 10⁻² μm.