In its orbit, the moon passes between the sun and the Earth and then behind the Earth. Relative to the Earth-sun plane, the moon's orbit is slightly inclined by about 3 degrees. Occasionally, the exact alignment of sun, moon and Earth produces a solar eclipse. This happens only when the moon is in the new phase and its orbit intersects the Earth-sun plane between the Earth and the sun. The moon blocks out the sun and its shadow passes over the Earth.
In the same month as a solar eclipse, when the moon is full, a lunar eclipse will occur. In a lunar eclipse, the moon passes through the Earth’s shadow, which causes its light to dim. If the moon passes through the part of the Earth’s shadow called the umbra, a total lunar eclipse will occur. If the moon passes only through the penumbra, a partial lunar eclipse will occur.
Return to the Moon
Since 1972, no one has set foot on the moon. However, there is a renewed effort for a lunar return. Why? In 1994, the orbiting Clementine probe detected radio reflections from shadowed craters at the moon's South Pole. The reflections were consistent with the presence of ice. Later, the orbiting Lunar Prospector probe detected hydrogen-rich signals form the same area, possibly hydrogen from ice.
Where could water on the moon have come from? It was probably carried to the moon by the comets, asteroids and meteors that have impacted the moon over its long history. Water was never detected by the Apollo astronauts because they didn't explore that region of the moon. If there is indeed water on the moon, it could be used to support a lunar base. The water could be split by electrolysis into hydrogen and oxygen -- the oxygen could be used to support life and both gases could be used for rocket fuel. So, a lunar base could be a staging point for future exploration of the solar system (Mars and beyond). Plus, because of the moon's lower gravity, it is cheaper and easier to lift a rocket off of its surface than from Earth.
It might tricky to get back there though, at least for U.S. astronauts. In 2010, President Barack Obama decided to cancel the Constellation program, the intent of which was to get Americans back on the moon by 2020. That means U.S. astronauts may have to hitch a ride with private space companies, which will receive some funding from NASA.
Other countries, including Japan and China, are planning to travel to the moon and researching how to build a lunar base using materials from the lunar surface. Various plans call for heading to the moon and establishing possible bases between 2015 and 2035.
To learn more about the moon, take a look at the links on the next page.