How does a phase differ from an eclipse?

Answer 1

It's a matter of perspective. When the Sun sets and it becomes dark, we don't call this an "eclipse", but it is similar; we're in the shadow of the Earth, the Earth's mass is blocking the Sun's light from getting to us. We call it "night". When the Moon moves into the Earth's shadow, we call it a "lunar eclipse", but it's really the same thing as "night on Earth, on the Moon".

Just as we have days and nights on the Earth, there are days and nights on the Moon. We don't live on the Moon (yet), so perhaps it isn't so obvious, but half of the Moon are having "daytime" and the other half is having "night". When we look at the Moon, we see that the bright part of the Moon (the part that's easy to see) is having daytime. If you look carefully, you can see the "night" part of the Moon as well; of course, it's night there, so it's dark. And since there are no electric lights or fires on the Moon, the only light the Moon gets at night is reflected Earthlight.