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Weird Science: The Origin and Features of the Moon

NGSS Science and Engineering Practices
NGSS Disciplinary Core Ideas

Written by contributing author Andrea Jones, Education and Public Outreach Specialist at the Lunar and Planetary Institute, NASA Goddard Space Flight Center


The current prevailing hypothesis for how our moon formed is known as the giant impact hypothesis. The giant impact hypothesis states that the moon was formed from debris caused by the collision of a Mars-sized object with Earth at least four billion years ago. Many planets in our solar system have moons, but Earth’s moon is the largest relative to the size of the planet. The moon is one-quarter the diameter of the earth. The moon’s size and relatively short distance from the earth make it the largest object in the night sky. In addition to its size, the moon is prominent because it is very bright. However, the moon does not produce light; but rather, reflects the light of the sun. The moon’s prominence and regular cycle of phases have contributed to its influence on language, art, mythology, and the calendar. The moon has not only inspired humans but has also contributed to our existence by making Earth a more habitable planet. For example, the moon moderates the wobble of the earth’s axis, which, in turn, stabilizes the climate.


One of the reasons for studying the moon is to understand more about the origin and geologic history of the earth. The moon provides information about how Earth formed. Because the moon’s surface is relatively stable and the moon has no wind or rain, its history of meteoric bombardment is preserved in its craters. This history has been largely erased on Earth by mountain building, volcanism, weathering, and erosion.


Early astronomers thought the large dark spots on the moon were oceans. Each lunar dark spot was named mare (pl. maria), the Latin word for “sea.” Further explorations of the moon revealed that these dark regions were formed by ancient volcanic eruptions and appear darker because of their basaltic rock composition. This makes them less reflective than the highland areas which are composed of light colored rocks.



Image caption

SF Fig. 6.1. The Latin names and English translations of selected lunar maria on Earth’s moon

Image copyright and source

Image courtesy of Luc Viatour/ from Wikipedia, modified by Joanna Philippoff

Latin naming conventions are still used for lunar maria (SF Fig. 6.1). Mare Tranquillitatis, also called the Sea of Tranquility, was the site of the first manned moon landing by the NASA Apollo 11 mission in 1969.

Exploring Our Fluid Earth, a product of the Curriculum Research & Development Group (CRDG), College of Education. University of Hawaii, 2011. This document may be freely reproduced and distributed for non-profit educational purposes.