is a great project for someone interested in astronomy, has access to a telescope
and lives in an area where the stars are clearly visible at night. Simply attach
a spectroscope to your telescope and a new world opens. |
spectroscopy started when Isaac Newton first observed sunlight dispersed by a
prism. He saw a rainbow of colour, and possibly may have observed absorption lines.
These dark bands which appear throughout the solar spectrum were first later described
by Joseph von Fraunhofer. Most stellar spectra share these two dominant features
of the sun's spectrum: emission at all wavelengths across the optical spectrum
(the continuum) with many discrete absorption lines superimposed on top. Fraunhofer
and Angelo Secchi were among the pioneers of spectroscopy of the sun and other
stars. Secchi is particularly noted for classifying stars into spectral types,
based on the number and strength of the absorption lines in their spectra. Later
the origin of the spectral types was found to be related to the temperature of
the surface of the star: particular absorption lines can be observed only for
a certain range of temperatures; because only in that range are the involved atomic
energy levels populated. The absorption lines in stellar spectra can be used
to determine the chemical composition of the star. Each element is responsible
for a different set of absorption lines in the spectrum, at wavelengths which
can be measured extremely accurately by laboratory experiments. Then, an absorption
line at the given wavelength in a stellar spectrum shows that the element must
be present. Of particular importance are the absorption lines of hydrogen (which
is found in the atmosphere of nearly every star); these are known as Balmer lines.
In 1868, Sir Norman Lockyer observed strong yellow lines in the solar spectrum
which had never been seen in laboratory experiments. He deduced that they must
be due to an unknown element, which he called helium, from the Greek helios (sun).
Helium wasn't conclusively detected on earth until 25 years later.
on this project!
can improve on this project by making your own spectroscope.
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