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Instructions
Understand why a lunar eclipse takes place. The moon casts no light on its own. What people perceive as the moon shining at night is actually sunlight reflecting off the moon. The same sunlight that causes the moon to "glow" also causes the earth to cast a shadow into space. A lunar eclipse occurs when everything lines up just right, and the earth's shadow falls across the moon.
Find out when the next full moon occurs, a lunar eclipse can only happen when the moon is full. A lunar eclipse will not occur every full moon because the alignment is not right. For an eclipse to occur the moon must be within 0.5 degrees of the earth's ecliptic plane or the line that passes through the center of the sun and earth. Since the moon orbits the earth by five degrees, the moon only has two chances each month too pass through the ecliptic plane.
Recognize the three basic types of lunar eclipses: penumbral, partial and total lunar eclipses. The earth's shadow is actually formed by two cone-shaped parts, the umbral or the inner shadow, and penumbral or the outer shadow that is created on each side of the umbral. A penumbral lunar eclipse happens when the moon passes through the penumbral portion of the earth's shadow, it is very difficult to see and most go by unnoted. In contrast, an umbral eclipse is highly visible and occurs when part of the moon passes through the penumbral. Because the moon rotates on an angle, one location can have up to three lunar eclipses a year or have none at all. A total lunar eclipse happens when the Earth's umbral shadow covers all of the moon and only occurs once every 360 years.
Research the Saros Cycle. This is an 18-year, one-day and eight-hour eclipse cycle discovered by the ancient Babylonian astronomer, Chaldeans. It is still used today by astronomers to predict lunar eclipses. The numbering sequence of the Saros is complicated and an amateur astronomer may need help at first to understand it.
Find out when the last lunar eclipse occurred in your region. This will allow you to calculate when the next eclipse will occur using the Saros cycle. In a five-millennium period, from 2000 BC to 3000 AD, there were 7,718 partial and total lunar eclipses.
Understand that lunar eclipses don't last very long. The length of a lunar eclipse will depend on how much of the earth's shadow the moon is passing through. The longest an eclipse can last is three hours and 40 minutes.