MAA Glossary

O


Objective:
The light-collecting element of a telescop.

Oblateness:
The depature of a planet from spherical form because of the centrifugal force of the rotation.

Occultation:
When a large celestial body hides a small one from view (as when the moon moves in front of a star or Jupiter over one of its moons), the event is usually termed occultation rather than eclipse.

Opposition:
A planet is in opposition when it is 180 degrees away from the sun.