AstronomyThomas Cooper

The spectroscopic technique used to assess the concentration or amount of a given species, such as the elements that make up a star.

The instrument that performs such measurements is a spectrometer or spectrograph.

Most large telescopes have spectrometers, which are used either to measure the chemical composition and physical properties of astronomical objects or to measure their velocities from the Doppler shift of their spectral lines.

Telescope – to capture radiation Dispersion Device – to spread the radiation

out into a spectrum Detector – to record the results

Most spectroscopic methods are differentiated as either atomic or molecular based on whether or not they apply to atoms or molecules. Along with that distinction, they can be classified on the nature of their interaction:

Absorption spectroscopy uses the range of the electromagnetic spectra in which a substance absorbs.

Emission spectroscopy uses the range of electromagnetic spectra in which a substance radiates (emits).

Scattering spectroscopy measures the amount of light that a substance scatters at certain wavelengths, incident angles, and polarization angles.

A luminous solid, liquid or dense gas emits at all wavelengths and produces a continuous spectrum.

A low-density, hot gas emits light whose spectrum consist of a series of bright emission lines that represent it’s chemical composition. (Emission Lines).

A cool, thin gas absorbs certain wavelengths from a continuous spectrum, leaving dark absorption lines. (Absorption Lines)

Spectral Emissions of a Supernova

(1787-1826) Physicists Catalogued over 600

absorption lines Now know as

Fraunhofer lines

Lines that represent wavelengths of light that were removed

(absorbed) by gasses present in the outer layers of the sun.

Ground State – normal energy state

Exited State – contains more than the

normal amount of energy

Ionized State – electron has

exceeded the maximum energy state

N81, an emission nebula

An interstellar cloud made mostly of hydrogen gas

excited by absorbing radiation emitted by

extremely hot stars.

Change in Energy State

Change in Vibrational State

Change in Rotational State

Absorption of additional energy

can boost the electron into even

higher orbitals within the atom.

As it cascades down to the

ground state, it emits photons,

each with a different energy and

wavelength.