The Caldwell Objects

1" in a mere four days. Clearly, Lampland contended,
such changes could not be related to
physical movements of material, since that would
imply matter being propelled across space at
supernatural velocities. Besides, any details that
vanished in the cloud mysterious-
46
ly reappeared, then disappeared, again and
again, in the same locations. Lampland concluded
that dark shadows — like those cast by
the Moon onto the Earth during solar eclipses —
were sweeping across the nebula to cause the
observed effects. Such shadows, he believed,
were cast by clouds of dust traveling very close
to the nebula's light source.
Investigation continued. Using Lick Observatory's
120-inch reflector visually under
excellent seeing conditions in 1959, George
Herbig zoomed in on R Monocerotis and found it
to be a tiny triangular nebula "about 5" long,
increasing in surface brightness toward the
southern apex, fading out smoothly to the north,
but with sharp, well defined edges on east and
west. No star could be seen. In poor seeing or
with low resolution, R Monocerotis would look
simply like a diffuse 12th-magnitude star." Then
in 1966 Frank Low and Bruce J. Smith announced
that R Monocerotis was a "cocoon" nebula — a
dusty envelope of gas (out of which planets
might form) around a newborn star. R
Monocerotis was the first nebula of this kind to
be discovered; astronomers had predicted their
existence just a year earlier. The team's evidence
was the large amount of infrared radiation that R
Monocerotis emitted relative to its output of
visible light. The scientists hypothesized that the
visible light ultimately came from a newborn star
at the center of a dusty cocoon 200 astronomical
units across. The l0th-magni-tude "knot" we see
in our telescopes as R Monocerotis, they argued,
is that cocoon of dust being illuminated from
within. In a sense this discovery was not new,
for, as Edwin Hubble reported in 1916, the 19thcentury
observer William Lassell believed R
Monocerotis was not a star—an opinion Edward
Emerson Barnard shared after viewing the
nebulous "star" with the 40-inch refractor at
Yerkes
The Caldwell Objects 183