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Manheim Township Astronomy: The Solar System and The Universe

tidally coupled

The locking of the rotation of a body to its revolution around another body through gravitational forcing. (also known as spin orbit lock)


The dividing line between daylight and darkness on a planet or a moon.


The edge of the apparent disk of a body, as in "the limb of the moon."


The lunar lowlands filled by successive flows of dark lava; from the Latin word for sea. (singular "mare").

sinuous rille

A narrow, winding valley on the moon caused by ancient lava flows along narrow channels.


Pulverized rock scattered by meteorite impacts on a planetary surface.


Ejecta from a meteorite impact, forming white streamers radiating from some lunar craters.

secondary crater

A crater formed by the impact of debris ejected from a larger crater.

multiringed basins

Very large impact basin in which there are concentric rings of mountains.


Meteorite of microscopic size. These meteorites are especially important for airless worlds as they produce regolith (ex: the moon).

relative age

The age of a geological feature referred to other features. For example, relative ages reveal that the lunar maria are younger than the highlands.

absolute ages

An age determined in years, as from radioactive dating.

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