Von Oppolzer found, in 1901, that Eros lost
three-fourths of its brilliancy once in every two hours and
thirty-eight minutes. Other observers have found slightly different
periods of variability, but none as long as three hours. The most
interesting interpretation that has been offered of this phenomenon is
that it is due to a great irregularity of figure, recalling at once
Olbers' hypothesis. According to some, Eros may be double, the two
bodies composing it revolving around each other at very close
quarters; but a more striking, and it may be said probable, suggestion
is that Eros has a form not unlike that of a dumb-bell, or hour-glass,
turning rapidly end over end so that the area of illuminated surface
presented to our eyes continually changes, reaching at certain times a
minimum when the amount of light that it reflects toward the earth is
reduced to a quarter of its maximum value. Various other bizarre
shapes have been ascribed to Eros, such, for instance, as that of a
flat stone revolving about one of its longer axes, so that sometimes
we see its face and sometimes its edge.
All of these explanations proceed upon the assumption that Eros cannot
have a simple globular figure like that of a typical planet, a figure
which is prescribed by the law of gravitation, but that its shape is
what may be called accidental; in a word, it is a fragment, for it
seems impossible to believe that a body formed in interplanetary
space, either through nebular condensation or through the aggregation
of particles drawn together by their mutual attractions, should not be
practically spherical in shape.
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