Lunar Eclipse

As seen by an observer on Earth on the imaginarycelestial sphere, the Moon crosses the ecliptic every orbit at positions called nodes twice every month. When the full moon occurs in the same position at the node, a lunar eclipse can occur. These two nodes allow two to five eclipses per year, parted by approximately six months. (Note: Not drawn to scale. The Sun is much larger and farther away than the Moon.)

A total penumbral lunar eclipse dims the moon in direct proportion to the area of the sun’s disk blocked by the earth. This comparison shows the southern shadow penumbral lunar eclipse of January 1999 (left) to the same moon outside of the shadow (right) demonstrates this subtle dimming.