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During his time spent on planetary
research, Slipher also managed to keep
investigating spectroscopic binary stars.
His work here led to a major break-
through, hailed by astronomers as a
milestone. He found that certain spectral
lines in the otherwise blurred spectra of
some stars were sharp and stationary,
and noted this phenomenon in a variety
of stars in Scorpius, Perseus, and Orion.
From this he concluded in 1909 that
interstellar gas must exist in widely
separated regions of space, producing
what he called “selective absorption of
light in space.” Some astronomers con-
gratulated Slipher for this conclusion, but
many others ignored the findings for a
long time. Observations in the 1920s
would finally prove Slipher correct.
Moreover, in December 1912, Slipher
used the spectrograph to discover the
presence of dust — or “pulverulent mat-
ter,” as he termed it — between the stars
of the famous Pleiades Cluster. Proving
that the dust near the star Merope in this
cluster was shining only by ref lected light
demonstrated the existence of stuff
between the stars; that stuff came to be
called the interstellar medium.
The breakthrough
The discovery of matter among the stars
of the Pleiades was a big one. This put
Slipher on the map, with a legitimate
claim to a major discovery in astrophys-
ics. He then turned toward solving the
biggest mystery of the age, the nature of
so-called spiral nebulae. These numer-
ous, faint, diffuse objects had remained
mysterious for a century and a half. The
German natural philosopher Immanuel
Kant had suggested they were separate,
large “island universes” of matter as early
as 1755. But the evidence of their nature
LEFT: The Slipher and Lampland families roll out
in the Lowell Stevens-Duryea car, with Verna
Lampland, Emma Slipher, and Marcia Slipher in the
back seat, and V.M. Slipher (driving), David Slipher,
and Carl Lampland in the front seat.
BELOW: V.M. Slipher made this image of a solar
eclipse expedition at Syracuse, Kansas, in 1918.
The discovery of matter among the stars of the Pleiades was a big one.
This put Slipher on the map, with a legitimate claim to a major discovery in astrophysics.