DK Eyewitness - Astronomy

Kirchhoff and bunsen
Following the invention of
the clean-flame burner by the
German chemist Robert Bunsen
(1811–1899), it was possible to
study the effect of different
chemical vapors on the known
pattern of spectral lines. Together,
Gustav Kirchhoff and Bunsen
invented a new instrument
called the spectroscope to
measure these effects. Within
a few years, they had managed
to isolate the spectra for many
known substances, as well
as to discover a few
unknown elements.
Eyepiece
Continuous
spectrum
Absorbing color
To prove his laws
of spectral analysis,
Kirchhoff used sodium
gas to show that when
white light is directed
through the gas, the
characteristic color
of the sodium is
absorbed and the spectrum shows black lines where the sodium should
have appeared. In the experiment shown above, a continuous spectrum (top)
is produced by shining white light through a lens. When a petri dish of the
chemical potassium permanganate in solution is placed between the lens
and the light, some of the color of the spectrum is absorbed.
Spectrum of the stars
By closely examining the spectral lines
in the light received from a distant star, the
astronomer can detect these “fingerprints” and
uncover the chemical composition of the object
being viewed. Furthermore, the heat of the
source can also be discovered by studying the
spectral lines. Temperature can be measured
by the intensities of individual lines in their
spectra. The width of the line provides
information about temperature, movement,
and presence of magnetic fields. With
magnification, each of these spectra
can be analyzed in more detail.
The spectrum
of potassium
permanganate
Micrometer (p.25)
Latticework frame
Prisms
Eyepiece
Norman lockyer (1836–1920)
During the solar eclipse of 1868, a
number of astronomers picked up a
new spectral line in the upper surface of
the Sun, the chromosphere (p.39). The English
astronomer Lockyer realized that the line did not coincide with
any of the known elements. The newly discovered element was
named helium (Helios is Greek for the sun god). It was not until
1895, however, that helium was discovered on Earth.
The spectroscope
A spectroscope uses a series of
prisms or a diffraction grating—a device
that diffracts light through fine lines to form
a spectrum—to split light into its constituent
wavelengths (pp.32–33). Before the era of
photography, an astronomer would view the
spectrum produced with the eye, but now it is
mostly recorded with an electronic detector
called a CCD (p.37). This 19th-century spectroscope
uses a prism to split the light.
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