Its hard to imagine the history of
Earth without our
Moon. For as long as man walked this
Earth, the Moon
served as "lesser light for the night" and faithful
time-piece. The phases of the Moon were used to help
guide the Harvest, or help determine the time of the
river floods.How our Moon came to existence is
still under speculation. There are several possible
scenarios:
- Fission Theory - the
Earth spinning so fast
during early formation that a piece broke off
forming the Moon
- Capture Theory - the Moon formed elsewhere
passed close to
Earth and was captured
- Co-Creation Theory - the
Earth and Moon
formed and evolved together
- Collisional Ejection Theory - a large piece
impacted the
Earth and broke off pieces of the
Earth and formed the Moon
The current champion of the Collisional Ejection
Theory: Solar System formation was a volatile
environment and collisions were common place. If the
Moon and
Earth formed together, the
orbit of the
Moon would be more circular and liberation (the
"wobble" of the Moon) would not be a factor. Also,
Moon rock does contain some "non-Earth" type rock
while also having some "Earth-like" features.
The Moon - A Quick Summary: (More information can be found on the Moon Fact Sheet)
 |
Average Distance from
Earth: |
384,400 km |
| Eccentricity of Orbit: |
0.0549 |
| Average Orbital Speed: |
3680 km/h |
| Orbital Period: |
29.531 days |
| Rotational Period: |
27.322 days |
| Inclination of Equator to
Orbit |
6.68º |
| Diameter: |
3,476 km |
| Mass: |
7.349 x 1022 kg |
 |
Average Density: |
3344 kg/m3 |
| Escape Speed: |
2.4 km/s |
| Albedo: |
0.11 |
| Maximum Surface
Temperature: |
130º C |
 |
| Minimum Surface
Temperature: |
-180º C |
| Average Surface
Temperature: |
N/A |
| Atmospheric
Composition |
None |
Back to Top Phases and Time: The
Moon has played a vital role in the formation of our
Calendar. The word "month" comes from a root word
"moon" or "moonth," the time it takes the Moon to go
from New Moon to New Moon. A close look at the
history of the Calendar can be found at the
NASA/Goddard Space Flight Center. There are so
many excellent diagrams for Lunar Phases that I
decided to use one instead of making my own (In the
meantime, there is a nice
Java applet available):
This image (Image
Credit) shows the position of the Moon and its
associated phase. For a cool application, NASA has a
What Will the Moon Look Like Tonight? tool.
Additional information can be found at the
Earth and Moon Viewer. Back to
Top Basic Structure: The Moon is
composed of two major features:
The Highlands are like our own mountain
ranges and are formed from igneous rock called
Anorthosite. These rocks date back to
about 4 billion years old. The Maria are similar
to our oceans, but were not formed by liquid.
The smooth appearance of the Maria is the result
of mare basalt rock, formed by past lava
flows - dating back to about 3.5 billion years.
The formation of the Moon ended pretty early
on as indicated by the dating of the rock. The
three basic methods of Lunar formation are:
- Differentiation - heavier elements sink
- Cratering - impacts by meteoroids
- Basin Flooding - impacts by large
meteoroids result in lava flows
This very nice lunar image (Image
Copyright 1999 by Calvin J. Hamilton) shows
the basic internal structures of the Moon.
While there is no global magnetic field, the
Moon is though to have a small Iron core
followed by a very thick mantle and a thin
crust. Back to
Top |
