William Huggins and his Spectroscopes
This is a memorable 'anniversary
day'. On 7 February 1824 William Huggins was born. He was never a professional
astronomer; he had to enter the family drapery business, and it was only when
he was able to retire from the firm that he was able to devote his whole time
to astronomy.
He set up an observatory at Tulse
Hill, in outer London, and concentrated on astronomical spectroscopy. A
spectroscope splits up light, and a normal star produces a rainbow band crossed
by dark lines, each of which is the trademark of some particular element or
group of elements. Huggins found that the stars could be divided into definite
types according to their colours; a red star showed a spectrum very different
from that of a white star - so that, for example, the orange Pollux has a
spectrum which is easily distinguished from that of a white star such as
Castor. Similar work was being carried out in Italy by the Jesuit astronomer
Angelo Secchi, and the stars were put into four distinct classes (the more
detailed Harvard classification system came much later):
I
White or bluish stars, with broad, dark spectral
lines due to hydrogen. Example: Sirius.
II
Yellow stars; hydrogen lines less prominent, but
more evidence of lines due to metals. Examples: Capella, the Sun.
III
Orange stars, with complicated banded spectra.
Example: Betelgeux.
IV
Red stars, with prominent lines due to carbon.
All were below magnitude 5, and many of them were found to be variable. R Cygni
in the Swan was a good example.
What about the nebulas? Some,
such as the Great Nebula in Andromeda, seemed to be made up of stars, but
others, such as the nebula in Orion's Sword, looked more like patches of gas.
Huggins knew that he could find out. The spectrum of a shining gas at low
pressure does not yield a rainbow; instead, it produces isolated bright lines.
When Huggins examined nebulae such as Orion's Sword, he saw only bright lines -
and this proved that the nebulae themselves were indeed gaseous. On the other
hand, the spectra of'starry nebulae' proved to be made up of the combined
spectra of many millions of stars. We now know that they are galaxies in their
own right, far beyond the Milky Way.
William Huggins died on 12 May 1910 at the age of 86.
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