Chapter 14
Spectrography
Abstract In this chapter, we introduce the concept of spectrography. Building on
the previous chapters on the nature of light and astronomical imaging, we discuss the
spectrograph and show through a simple practical how to take, reduce, and interpret
our first astronomical spectrum.
14.1 Introduction
Spectrography is one of the principal methods through which astronomers investigate the universe. The existence of dark absorption lines and bright emission lines
set against the broad continuum emission and their unique association with energy
changes, as discussed in Sect. 2.2, has enabled astronomers to to accomplish the
following things:
• From the shift of a line relative to its normal position we can determine velocity
and redshift and cosmological distance as well as infer the existence of exoplanets.
• From the width and strength of the lines we can determine relative abundances of
elements and molecules as well as the temperature of the body.
• From the shape of the line, we can determine the pressures, density, and rotational
characteristics of the body and infer the presence and strength of its magnetic field.
• The measurement of the continuum part of the spectrum, that part without lines,
enables us to observe nonquantised emission processes and to determine the spectral energy distribution of the body.
Hence, spectrography provides us with a set of tools that allow us to determine a
wide range of physical characteristics.
© Springer Nature Switzerland AG 2020
M. Gallaway, An Introduction to Observational Astrophysics,
Undergraduate Lecture Notes in Physics,
https://doi.org/10.1007/978-3-030-43551-6_14
197
Spectrography
Abstract In this chapter, we introduce the concept of spectrography. Building on
the previous chapters on the nature of light and astronomical imaging, we discuss the
spectrograph and show through a simple practical how to take, reduce, and interpret
our first astronomical spectrum.
14.1 Introduction
Spectrography is one of the principal methods through which astronomers investigate the universe. The existence of dark absorption lines and bright emission lines
set against the broad continuum emission and their unique association with energy
changes, as discussed in Sect. 2.2, has enabled astronomers to to accomplish the
following things:
• From the shift of a line relative to its normal position we can determine velocity
and redshift and cosmological distance as well as infer the existence of exoplanets.
• From the width and strength of the lines we can determine relative abundances of
elements and molecules as well as the temperature of the body.
• From the shape of the line, we can determine the pressures, density, and rotational
characteristics of the body and infer the presence and strength of its magnetic field.
• The measurement of the continuum part of the spectrum, that part without lines,
enables us to observe nonquantised emission processes and to determine the spectral energy distribution of the body.
Hence, spectrography provides us with a set of tools that allow us to determine a
wide range of physical characteristics.
© Springer Nature Switzerland AG 2020
M. Gallaway, An Introduction to Observational Astrophysics,
Undergraduate Lecture Notes in Physics,
https://doi.org/10.1007/978-3-030-43551-6_14
197