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Section 1
Earth's moon, Luna, is about 1/4 the size of Earth. It is roughly 3476 km in diameter. It has only about 1/6 the gravity present on Earth. This means that to calculate your "moon weight", you divide your Earth-weight by six.
The moon rotates on its axis every 29
1/2 Earth-days. It also revolves around the Earth in the same
amount
of time. Because of this fact, one moon-day is exactly as long
as one
moon-year. A
day on
the moon is the same length as a year! Also,
it means that the same side of the moon ends up facing the Earth
all
of the time. In fact, that side of the moon has developed a
bulge,
due to the constant effect of Earth's gravity. The moon is
approximately 4.6 billion years old based on data from the
Apollo
missions. It certainly appears that the moon is just about the
same
age as the Earth. This was not always thought to be the case.
Arguments have been made in the past in support of the age of
the
moon being either much greater, or much less than the Earth's
age. We now believe that about 4.5 billion years ago, soon
after
the Earth formed, a large object, about the size of Mars
collided with
this early Earth. This earliest version of Earth was
completely
devastated, and enough material was blown out into space by the
impact
to create the moon out of the "debris". The moon has been
with
us, each night, ever since.
The moon has several interesting, and highly visible, features.
Highlands: Highlands on the moon are higher, lighter areas on the moon's surface.
Altitudes of the moon's highlands can reach 8000 meters! (That's about 3 miles!)
Lowlands: Lowlands on the moon's landscape are lower, darker areas. Some lowlands are termed "Maria", a Latin word meaning "seas". Long ago, ancient astronomers believed that the moon was covered with liquid water. The Maria were large basins containing the moon's "seas" and "oceans". There are a total of fourteen maria or "seas" on the moon. (Ex: Mare Imbrium-sea of dreams; Mare Tranquillitatis-sea of tranquility; Oceanus Procellarium- Ocean of storms; etc.) It is important to note that there is ABSOLUTELY NO EVIDENCE OF WATER ON THE MOON TODAY, OR AT ANY TIME IN THE PAST. Never had it, never will.
Craters: Craters are evidence of the great impacts that have occurred on the surface of the moon throughout its long history. The largest crater on the moon is CRATER COPERNICUS, which is about 91 km in diameter.
Rays: Rays are light colored streaks of dust that extend from the edges of craters in a star-like pattern. Rays are the result of the low gravity on the moon's surface. They are a type of "splash effect" seen only in low gravity situations.
The moon is a desolate place. It has no atmosphere to speak of, and therefore, no weather of any kind. The surface of the moon is not exposed to the forces of erosion or weathering, as are surfaces here on Earth. The lack of erosion means that the surface of the moon doesn't change very much over time. The footprints that the astronauts left in 1969 are still up there in the dust, looking pretty much the way that they did when they were put there over 30 years ago. Average temperatures on the surface of the moon vary greatly from night to day. Daytime temperatures reach +127 degrees F, while nighttime temps dip to near -173 degrees F!
The moon shines by reflected light, producing no light of its own. We on Earth see a different section of the lighted portion of the moon each night, so therefore, we see "phases" of the moon. Every 29 1/2 days the moon goes through all of its phases, as it makes its orbit around the Earth.
Large objects in space, like planets and moons cast different shadows than we do here on Earth. The large shadows cast by celestial bodies have two parts. An umbra is the inner, darker part of the shadow. A penumbra is the larger, outer, lighter portion of the shadow.
When the moon is in the Earth's umbra, we see a Total Lunar Eclipse.
When the moon is in the Earth's penumbra, we see a Partial Lunar Eclipse.
When the Earth is in the moon's umbra, we see a Total Solar Eclipse. A Total Solar Eclipse is a fairly rare phenomenon and worth further study. Follow this link to an image of a total solar eclipse. Once you're there, you may follow other links to interesting sites devoted to this spectacular occurrence.
When the Earth is in the moon's penumbra, we see a Partial Solar Eclipse.
The moon's gravity also affects the Earth, in that it causes a bulge to occur in our oceans. These bulges are called "tides". Every 24 hours on Earth there are two high tides and two low tides in most places. These are called semidiurnal tides. Maine has this sort of tide system. Every six hours, in a given spot, the oceans goes from being at high tide, to low tide. If there's a high tide somewhere at noontime, by six PM, the tide will be a low as it gets. By midnight, the tide would be back to being as high as it gets. In some parts of the world there are only two tides each day, one high and one low, these are called diurnal tides. The high tide on the side of the Earth facing the moon is called a Direct Tide. The high tide on the side of the Earth not facing the moon is called an Opposite Tide. During certain phases of the moon, especially the full moon and new moon, the gravity from the moon works with the gravity from the sun, both sort of pulling in the same direction. This causes a higher than normal high tide called a Spring Tide. At other times during the month, the moon's gravity works against the sun's gravity. The forces sort of cancel out partially, and the high tide is much lower than normal. This is called a Neap Tide, and these tides occur during the first and last quarter phases of the moon.
