Same Moon for all
People around the Earth see nearly the same phase.
Two friends
One friend lives in the East of the country and another in the West. Both look at the Moon on the same day.
Do they see the same phase?
What this lesson covers
The idea
Because Earth's rotation period of one day is much shorter than the Moon's revolution period of nearly a month, people in different parts of Earth see nearly the same phase on a given day.
Two friends
One friend lives in the East of the country and another in the West. Both look at the Moon on the same day.
Do they see the same phase?
- Nearly the same
- Totally different
- One sees full and the other sees new
Compare the cycles
Open both tabs.
Slow Moon, fast Earth
The Earth turns once in a day, but the Moon takes nearly a month to go round. So on one day the Moon hardly changes its phase, and people everywhere see nearly the same phase.
Earth rotates in 1 day; the Moon revolves in nearly a month. So on a given day people in different parts of Earth see nearly the same phase.
Notes
Earth rotates in a day, the Moon revolves in nearly a month: same phase all over Earth.
Check yourself
On a given day, people in different parts of the Earth see …
The Earth completes one rotation in …
The Moon completes one revolution around the Earth in nearly …
The phase is nearly the same everywhere because the Earth's rotation period is …
- completely different phases. The Moon changes slowly, so the phase is nearly the same.
- no Moon at all. They see nearly the same phase.
- nearly the same phase — correct. Yes!
- one day — correct. Yes!
- one month. That is about the Moon's revolution period.
- one year. That is the Earth's revolution period.
- a day. That is the Earth's rotation period.
- a month — correct. Yes!
- an hour. It takes nearly a month.
- much longer than the Moon's revolution period. The Earth's rotation period is much smaller.
- exactly equal to it. The Earth's rotation period is much smaller.
- much smaller than the Moon's revolution period — correct. Yes!