Earth's Two Shadows

Did you know that Earth has two shadows? Tonight (and early tomorrow morning) you can see their effect in a lunar eclipse as the Moon crosses through the outer edge of Earth's shadow in space.

Every celestial body has two shadows, and for a very simple reason. Imagine holding a baseball at arm's length up to a ceiling light. As you start to cover the light's face you can see part of but not the entire light face, up until it's fully obscured and you're completely in the baseball's shadow. In that transition phase when only part of the light's is visible, you're watching the first shadow cover your eye. At this point you are receiving some direct light and also some shadow. The second type of shadow is where your eye is in the shadow of the baseball completely and no light from the source is reaching you directly.

Tonight's lunar eclipse is caused by the first kind of shadow, where the Earth partially crosses in front of the Sun as seen from the Moon's perspective, resulting in a slightly darker appearance from Earth. You won't see any distinctive shadow lines, but you can test your observing acuity by taking note of by how much (or even if) the Moon's face appears to dim.