Photograph taken at the Royal Observatory, Cape of Good Hope
]
On Monday, September 18, the brilliancy of the comet attracted popular
attention throughout the country, and the “blazing star” near the sun
was the one topic of conversation. In the small telescope it presented
the aspect of a brilliant nebulous mass, having on each side curved
appendages like horns or wings, nearly as large as the central body, and
at their base quite as brilliant, the general form of the whole
reminding one of the winged globes carved on ancient monuments. This
appearance, doubtless due to the outbreak of glowing vapors from the
nucleus, was also exhibited, although to less extent, on the following
two days, during both of which the comet remained visible to the naked
eye.
Observations made of the comet with large telescopes showed that the
nucleus had separated into six or eight star-like knots strung like
pearls along a luminous streak some fifty thousand miles in length. The
largest of these knots was some five thousand miles in diameter, an
interesting fact as compared with the size of the earth, which is 7,925
miles, according to the British Astronomical Association Handbook for
1925.
A faint straight-edged beam of light, or “sheath,” accompanied the
comet, enveloping the head and projecting like a hood three or four
degrees in front. Besides this, three or four irregular shreds of
cometary matter were detected, escorting the comet, as it were, like
airplanes, at a distance of three or four degrees when first seen, but
gradually receding from it, and at the same time growing fainter. The
actual length of the comet’s train at one time exceeded one hundred
million miles, more than the distance of the sun from the earth. (If the
head of the comet had rested on the earth, and its train stretched
outward toward the sun, it would have extended seven million miles
beyond that luminary.)
The trains of comets have been grouped under three types, _viz._, the
long straight rays as shown in the photograph of Halley’s comet, though
this was only one of the many outlines assumed; the second is the
curved, plume-like train resembling that of the comet of Donati; and
thirdly the short stubby brushes violently curved. The great Daylight
comet had a greatly curved train belonging to the second type, and it
was mainly composed of carbon compounds. The curvature of the train was
due to matter for which the repulsive force is only a fraction of the
gravitational force. The pressure of light from the sun was a most
important factor in the formation of its train.
When the fierce pressure of the sun’s light strikes upon the particles
forming the train, it drives the particles which are of the same
relative size as the particles of light along with them, just as when
the waves of the sea break against a beach they tend to drive small
pebbles and sand upward along the beach.