Selenology Today # 7 July 2007 - Home

HISTORICAL NOTE SELENOLOGY TODAY # 7
These discoveries by Kirchhoff and
Bunsen made it possible to identify
elements in solar and stellar spectra. In
1868, Joseph Lockyer and Pierre Jannsen
predicted the presence of a new
previously undescribed element (helium)
in the sun.
Figure 2 Author’s photograph of a
spectroscope slit and adjacent spectra
of a fluorescent light source showing
multiple bright emission lines.
Photographic recording of astronomical
spectra improved during the nineteenth
century as the Daguerreotype method
(1839) was replaced first by the
colloidion wet process (1851) and later
by dry photographic plates (1880s). The
latter were capable of recording features
fainter than the unaided eye could
discern. The first image of the moon
showing any features was made by John
William Draper in 1841. The
Daguerreotype process used required an
exposure of 20 minutes using a 12 inch
(30 cm) diameter telescope. However,
much could be done with even primitive
equipment and Henry Draper was able to
photograph the spectrum of Vega in 1872
page 48
using a 28 inch (71 cm) diameter
telescope. By 1880, Draper’s clock drive
allowed exposures of 50 minutes and he
was able to photograph the Orion nebula
(M42). Figure 3, courtesy of the
Smithsonian Institute archives, shows
Henry Draper with a small telescope
equipped for photography. He
subsequently improved the clock drive
and was able to obtain the spectrum of
the Orion Nebula and the spectrum of the
Tebbutt’s comet of 1881. Draper
eventually recorded the spectra of about
one hundred stars and began the
classification system which was later
further developed by Annie Jump
Cannon and Edward C. Pickering toward
the end of the nineteenth century and
which is still in use today. He also
photographed spectra of the moon,
Jupiter, Mars, and Venus.
Figure 3 Courtesy of Draper Family
Collection, Archives Center, National Museum
of American History, Behring Center,
Smithsonian Institution.