Back to the list
Keep going · science
Phases of the Moon
A small piece of thinking
Does the Moon change its shape?
No. In the night sky it looks as if the Moon changes — sometimes a thin crescent, sometimes a half circle, sometimes fully lit and sometimes almost invisible. But the Moon always has the same shape: it is a giant ball.
Half of the Moon is lit by the Sun. The other half is in shadow. That is always true.
So what changes? What changes is the place we are looking from.
The Moon orbits the Earth. As it moves, we on Earth see a different part of that lit half each time. We call these the phases of the Moon — new moon, first quarter (waxing), full moon, last quarter (waning).
One orbit of the Earth takes about 29 and a half days.
A bigger piece of thinking
What would the Earth look like from the Moon?
Imagine you are standing on the Moon, looking at the Earth.
What would the Earth look like from the Moon if the Moon were at new moon? And at full moon? And at first and last quarter? Would people on that part of the Earth have day or night?
Now imagine standing on the Moon and looking at the Earth.
When we have a new moon (we can barely see the Moon), from the Moon we would see the whole of the Earth lit up.
When we have a full moon, from the Moon we would see the Earth almost entirely dark.
At first or last quarter the Earth would look like a half circle.
And what about day and night? Where the Earth is lit, it is day. On the dark side it is night.
A large piece of thinking
Why is there not an eclipse of the Moon at every full moon?
Work out how the positions of the Sun, the Earth and the Moon on this Koumio® board differ from the real ones.
On the model it can look as if the Earth must cast a shadow on the Moon at every full moon. So why does that not happen out in space?
Because the Moon does not orbit in exactly the same plane as the Earth orbits the Sun.
Its path is slightly tilted. Most of the time the Moon at full moon passes above or below the Earth's shadow. Only sometimes do all three bodies — Sun, Earth and Moon — line up exactly. That is when an eclipse happens.
Keep going
- 1
Find the Sun, the Earth and the Moon on the board.
- 2
Look at the Moon through the eyepiece mounted on the Earth.
- 3
Take hold of one of the space stations and turn the Moon around the Earth.
- 4
Figure out how the view of the lit and shadowed parts of the Moon changes as seen from the Earth through the eyepiece. Try to picture how the positions of the Sun, the Earth and the Moon change relative to one another.
Next time you see it
Next time you see the Moon at night, ask yourself:
Where is the Sun right now?
Where is the Earth?
How much of the lit half am I seeing?
This is how scientists think.
More curiosity questions
- Do we see the whole universe when we look at the night sky?
- What would happen if the Moon stopped?
