Planet Earth or Earth planet

Planet Earth is correct.

In the first one planet is specified and in the second it is understood Earth is a planet.

Right, so these are correct:

1- Planet Earth

2- Earth.

Thank you very much for your time Vsuresh.

Can you please explain why is it ok to say "New York city" but not " City New York" ? / "Planet earth" but not "Earth planet" ?

I want a grammatical explanation please.

Thank you again.

There is no 'grammatical explanation' beyond the fact that it is the wrong English sentence structure. 'New York City' is the city's name; 'Earth' is the planet's name.

Thank you very much for your time Mister Micawber.

So can I say " Galaxy Milky way" or " River Nile" ?

Galaxy Milky Way-- No.

River Nile-- Yes

You must learn these individually: 'The River Nile' but 'the Mississippi River'.

Planet Earth is correct.

The reason is the word order in English names.-

We do not say Theresa Mother, but Mother Theresa.

We do not say John Saint, but Saint John.

We do not say Jesus baby, but baby Jesus.

We do not say Obama President, but President Obama.

We do not say Christmas Fat

Can I say " The Nile river" ? If so, what is the difference?

My problem is this. I am going to teach an English reading lesson about Earth. The title of this lesson is "Earth Planet".

I know for sure that this title is wrong and should not be written like this. But I don't know WHY and therefore can't explain it to my students.

How would you explain it?

Thank y

I think you have to tell them that it is idiomatic between and often within groups. We have already seen various examples here.

The planet Mars, the constellation Orion, the Nile River or the river Nile, the Mississippi River (not 'the river Mississippi'), the baby Jesus, Lake Michigan vs the Great Salt Lake, Mount Etna vs Brokeback Mountain, County Cork vs Cook County, etc.