The Sun Always Lights Up Half of the Moon
The Sun always illuminates one half of the Moon; the Moon's phases are caused by how much of that lit half we can see from Earth.
Half, always. NASA says the Sun always lights the side of the Moon facing it. The phases come from how much of that lit half we see from Earth.
Explanation
The Moon seems to grow and shrink over a month, but nothing about the Moon itself is changing. NASA puts it plainly: the shape of the Moon isn’t changing throughout the month. The Sun’s light comes from one direction, and it always illuminates one half of the Moon, the side that is facing the Sun. What changes is our view. According to NASA, our view of the illuminated part of the Moon changes each night, depending on where the Moon is in its orbit around Earth. When we have a full view of the lit side, that is a full moon. When the side facing Earth is dark, that is a new moon. NASA adds one more correction to everyday language. What is called moonlight is actually just sunlight reflecting off the Moon’s surface.
Source and verification
- Source
- NASA Tier A
- Last verified
- Confidence
- 95 out of 100
- Verified by
- Ali Ahmad Chaudhry