Penumbral lunar eclipse: On Friday, October 18, the moon will pass through the edge of Earth's shadow, resulting in a 'penumbral eclipse.' It's a subtle effect, and won't be visible in much of North America.
Friday's lunar eclipse will be the least dramatic of the three kinds of lunar eclipse: total eclipse, partial eclipse, and penumbral eclipse.
What's the difference? Location, location, location.
In a total lunar eclipse, like the one seen in the picture above (see a bigger version here), the sun, moon, and Earth are perfectly aligned, and the Earth's shadow completely covers the moon. As the eclipse starts, and the three bodies are moving into perfect alignment, the Earth's shadow sweeps across the moon's face until it is totally darkened, at which point the moon appears to have an unearthly reddish color, due to the sunlight filtering through Earth's atmosphere and painting the moon with a sunset-red glow. That lasts a few minutes or hours, depending on the Earth's and moon's orbits, and then the Earth's shadow sweeps off the moon.