That depends on what kind of eclipse we're talking about! In general terms, an eclipse is caused by one planetary body passing in front of another and blocking light from the sun, basically casting a shadow across the blocked body. In a solar eclipse, which are relatively rare, the earth, moon, and sun line up so that the moon is directly in between the earth and sun, and the moon's shadow falls across the earth, putting the earth's surface in darkness. In a lunar eclipse, the earth orbits in between the moon and the sun, and the shadow of the earth falls across the face of the moon, making it appear darkened or slightly reddish.

An eclipse of the sun happens when the moon is at just the right distance from the earth, and in line with the earth and the sun, so that the disk of the moon just exactly covers the disk of the sun, from our viewpoint -somewhere on Earth.

It's like this: if you look at someone's face across the room, and close one eye, and put your finger in front of your open eye, you can block out all or part of the person's face from your viewpoint if you move your finger in and out from your own face.If your finger is not exactly in line with your open eye and the person's face, you won't block their face; if your finger is farther away, it looks smaller than the face, so you may block out a portion of the face - that's like a partial eclipse. If your finger is at just the right distance, you can block out the whole thing. Now, leave your finger there and close this eye, and open the other eye. What happens? You see the face again! That's like being at another location on the earth - they don't have an eclipse.

Eclipses of the sun happen only at new moon, when the moon is between the earth and the sun.

An eclipse of the moon happens when the earth blocks the sunlight from hitting the moon. It happens only at full moon.

An eclipse is where an object obscures another object in the sky. A solar eclipse happens when the moon is between the earth and the sun, thus blotting out the sun's light. A lunar eclipse is when the earth is between the sun and the moon, thus blotting out the sun's light that falls on the moon (causing the moon to go dark).

Most of the time, when you see a picture of an eclipse with a white rim surrounding a black disk, it's a solar eclipse (the black disk is the dark side of the moon, and the white rim is the edge of the sun peeking around the moon). Lunar eclipses are far more common, but far less spectacular.