Replies:
It all depends on what you mean by "biggest" -- brightest, largest,
or most massive...
Brightest: the _apparent_ brightness of a comet is a function of its
orbit: how close to the Sun does it get and how close to the Earth.
Even when a comet's orbital elements are well-known, you cannot reliably
predict how bright it will be as seen from the Earth: some of us may
remember the ballyhoo about Comet Kohoutek back in 1978(?), and Halley's
1986 apparition was much dimmer than expected (I remember having trouble
even finding it with binoculars).
Largest: not much is known about the actual size of comets because all
we can see is the light emitted and reflected from the comet's coma
and tail *except* when comets pass across the face of the Sun: then, we
never see a sillouette, which means that comets must have radii less
50 km.
Heaviest: again not much is known except an upper limit based on the
fact that comets do not measureably affect the orbits of planets they
closely approach. This upper limit is 1/1,000,000 times the mass of
the Earth.
Ask me more! I know a bit about comets having been an official observer
at the Joint Observatory for Cometary Research run by NASA and N. M. Tech
for several years.
NEWTON is an electronic community for Science, Math, and Computer Science K-12 Educators, sponsored and operated by Argonne National Laboratory's Educational Programs, Andrew Skipor, Ph.D., Head of Educational Programs.
