Eclipse Lunar

A lunar eclipse is an eclipse which occurs whenever the moon passes behind the earth such that the earth blocks the sunÕs rays from striking the moon. This can occur only when the Sun, Earth, and Moon are aligned exactly, or very closely so, with the Earth in the middle. Hence, there is always a full moon the night of a lunar eclipse. The type and length of an eclipse depend upon the MoonÕs location relative to its orbital nodes. The shadow of the Earth can be divided into two distinctive parts: the umbra and penumbra. Within the umbra, there is no direct solar radiation. However, as a result of the SunÕs large angular size, solar illumination is only partially blocked in the outer portion of the EarthÕs shadow, which is given the name penumbra. A penumbral eclipse occurs when the Moon passes through the EarthÕs penumbra. The penumbra causes a subtle darkening of the Moon's surface. A special type of penumbral eclipse is a total penumbral eclipse, during which the Moon lies exclusively within the EarthÕs penumbra. Total penumbral eclipses are rare, and when these occur, that portion of the Moon which is closest to the umbra can appear somewhat darker than the rest of the Moon. A partial lunar eclipse occurs when only a portion of the Moon enters the umbra. When the Moon travels completely into the EarthÕs umbra, one observes a total lunar eclipse. The MoonÕs speed through the shadow is about one kilometer per second (2,300 mph), and totality may last up to nearly 107 minutes. Nevertheless, the total time between the MoonÕs first and last contact with the shadow is much longer, and could last up to 3.8 hours. The relative distance of the Moon from the Earth at the time of an eclipse can affect the eclipseÕs duration. In particular, when the Moon is near its apogee, the farthest point from the Earth in its orbit, its orbital speed is the slowest. The diameter of the umbra does not decrease much with distance. Thus, a totally-eclipsed Moon occurring near apogee will lengthen the duration of totality.