- oceanus
- literally "ocean"; really a large
circular plain
- old
- a planetary surface that has been modified little
since its formation typically featuring large
numbers of impact craters (compare young).
- Oort, Jan Hendrik
1900-1992
- Dutch astronomer made major contributions to
knowledge of the structure and rotation of our
galaxy. More or less as a sideline, Oort studied
comets as well. The result of this work was a
theory, now widely accepted, that the Sun is
surrounded by a distant cloud of comet-stuff, now
called the Oort cloud, bits of which are
occasionally hurled into the solar system as
comets.
- opposition
- A planet is said to be "in opposition"
when it is directly on the opposite side of the
Earth from the Sun. This is generally the closest
it comes to the Earth and the time at which it is
most easily visible.
- ovoid
- shaped like an egg
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