* The rotation period of the Moon is the same as the period of its revolution about the Earth. This arrangement keeps the same face of the moon turned toward the Earth.
* The distance to the Moon averages 384,400 km but can be as large
as 406,700 km and as small as 356,400 km. The Moon's diameter
is about 1/4 that of the Earth.
* The two parts of the shadows of the Earth and the Moon are the
penumbra, within which sunlight is partially blocked, and the
umbra, within which sunlight is completely blocked. Total eclipses
occur within the umbral shadow.
* The Moon's umbral shadow is only about 150 km wide where it
reaches the Earth. During a solar eclipse, the Moon's umbral shadow
sweeps rapidly across the Earth, producing an eclipse track that
covers less than 1% of the Earth's surface area.
* Eclipses can occur only when the Moon is in its new or full
phase and when the Moon is near the ecliptic. Eclipses occur in
series in which successive eclipses are separated by 18 years,
111/3 days, the saros period. Using their knowledge of the saros,
ancient astronomers were able to predict eclipses.
* Tides cause the day to lengthen and the Moon to recede slowly
from the Earth. In the remote future, the day and month may become
equal in length. When that happens, the Earth will keep the same
face turned toward the Moon.
* The Moon's surface is covered with craters. The meteoroids that
made the craters have fragmented the Moon's surface layers and
produced a fine layer of debris.
* The lunar maria were produced when vast volcanic flows flooded
the floors of basins produced by earlier impacts. Little or no
volcanic activity has taken place for more than 3 billion years.
* Analysis of lunar samples has shown that they are similar to
the surface rocks of the Earth but lack water and are deficient
in easily vaporized elements, such as chlorine, zinc, and lead.
Lunar rocks range in age from 3.2 billion to 4.5 billion years.
The terrae are about 1 billion years older than the maria.
* Measurements of the crater densities of regions of the Moon
that have different ages have been used to show that the Moon
experienced an early period of intense bombardment. The relationship
between crater density and age for the Moon has been applied to
other planets and satellites to estimate their ages.
* The Moon has almost no atmosphere because any gases that enter
the atmosphere escape almost immediately. These gases come from
the solar wind and radioactive decays in lunar surface rocks.
* The average density of the Moon is too small to permit a large
metallic core. Seismic studies show that the Moon's interior is
virtually inactive. The crust and lithosphere of the Moon are
both very thick compared with the Earth's.
* Old theories of the origin of the Moon all suffered from serious
deficiencies. A new theory, which proposes that the Moon accumulated
from debris from an impact of a large body with the Earth, accounts
much more successfully for what we know about the history and
composition of the Moon.
annular eclipse, ascending node, Baily's
beads, binary accretion theory, capture theory, corona
crater density, crater saturation, descending node, diamond ring,
eclipse season, eclipse track, eclipse year
fission theory, giant impact theory, line of nodes, maria, mascon,
penumbra, rays, regolith, rilles, saros, sidereal month, sinuous
rille, synchronous rotation, synodic month, terrae, umbra
1. What kind of eclipse do we see when the moon is entirely within the Earth's umbral shadow? total lunar
2. At which phase of the moon do solar eclipses occur? new
3. If a lunar eclipse occurs tonight, when is the soonest that
a solar eclipse can occur? in two weeks
4. Which of the following is a consequence of the fact that the
rotation and revolution periods of the moon are the same? the
moon keeps the same fact turned toward the earth
5. The surface of the Moon has changed little in the past 2-3
billion years
6. Compared to the lunar maria, the lunar uplands (terrae) are
more cratered, older
7. The lunar maria were formed by lava flows into low areas
8. One of the most important results of the Apollo missions to
the Moon was the determination of the age of moon rocks
9. One hemisphere of a newly discovered satellite is much more
heavily cratered than the other hemisphere. What can be said of
the more heavily cratered side of the satellite? it is older than
the other side
10. A recent theory attributes the origin of the moon to the impact
of a Mars-size body with the Earth. Which of the following is
both a true statement and supports the impact theory of the moon's
origin? the composition of the moon is similar to Earth's but
somewhat different in two weeks
4. Which of the following is a consequence of the fact that the
rotation and revolution periods of the moon are the same? the
moon keeps the same fact turned toward the earth
5. The surface of the Moon has changed little in the past 2-3
billion years
6. Compared to the lunar maria, the lunar uplands (terrae) are
more cratered, older
7. The lunar maria were formed by lava flows into low areas
8. One of the most important results of the Apollo missions to
the Moon was the determination of the age of moon rocks
9. One hemisphere of a newly discovered satellite is much more
heavily cratered than the other hemisphere. What can be said of
the more heavily cratered side of the satellite? it is older than
the other side
10. A recent theory attributes the origin of the moon to the impact
of a Mars-size body with the Earth. Which of the following is
both a true statement and supports the impact theory of the moon's
origin? the composition of the moon is similar to Earth's but
somewhat different