aasmaan= sky
meiN= in ( capital N is half sound of english letter "N")
tara= star ( singular)

if you want to say 'star of the sky' then it is :
aasmaan ka tara

the star in the sky
aasmaan mein tara OR
falak pe tara OR
If you wish to say it in more of a polished urdu you can say "falak mein tara or najam" and if you wish to say in simple urdu you can say aasmaan mein tara.