Total lunar eclipses

Unlike a solar eclipse, a lunar eclipse is visible over a larger area to everyone who can see the Moon, because its source of illumination - the Sun - is cut off by the Earth.

One of the best ways to view a total lunar eclipse is with binoculars. A powerful telescope will give you a close-up view of the shadow moving slowly over the craters, but with their wide views and sharp optics, binoculars give you a striking perspective on the entire drama of totality.

A lunar eclipse begins when the Moon enters the outer fringe of Earth's shadow, called the penumbra, causing a very subtle diminution of light on the Moon. In the case of penumbral eclipses, the Moon moves only through this outer part of the shadow, which, at the Moon's distance, is over 16,000 kilometers in diameter. Most observers on Earth usually don't notice much difference in the Moon's brightness until a half hour or so into the penumbral phase.

As the Moon penetrates deep into the penumbra, it enters the darker core of Earth's shadow, called the umbra, and that aspect is very noticeable indeed. At this time, the partial phases of the eclipse get underway, as observers watch the curved shape of Earth's shadow gradually close over the Moon. Aristotle, as well as other ancient observers, cited the round shape of Earth's shadow cast on the Moon during a lunar eclipse as one of the earliest proofs that Earth is spherical.

The total phase of the lunar eclipse begins about two and a half hours later as Earth's umbral shadow, which is about 9,000 kilometers across, engulfs the Moon. If the Moon skirts the inside of the cone-shaped umbra, the total eclipse phase will be short, about 45 minutes or less. If it crosses the central part of the umbra, the total phase can last over two hours and the Moon will appear darker.

At totality, the most eerie aspect of a lunar eclipse occurs. The Moon is illuminated by sunlight refracting (bending) through Earth's atmosphere. The blue light is bent the least, but the red light is bent the most, just as it is at sunset or sunrise, and it falls on the Moon. Hence, the Moon takes on a dull, coppery hue. In binoculars, brighter stars can often be seen shining next to the Moon's limb, making the whole scene look like a large ruby set among tiny diamond chips. A lunar eclipse, though not as awe-inspiring as a solar eclipse, nonetheless gives skywatchers an opportunity to see how our nearest neighbor, whose appearance among the stars we take for granted, can be made to look distinctly unusual in its usual place.

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