"Many stars are shining in the sky."
Translation:Multaj steloj brilas en la ĉielo.
No, the -n ending would indicate that they shine INTO the sky; -n indicates movement with such dual-purpose prepositions.
Just as in German - "in den Himmel" (accusative) would be movement, "im Himmel" (dative) would be location. (Though with "sky" it would be "an den Himmel, am Himmel".)
You could also say estas brilantaj for "are shining" if you want to be explicit about the on-going nature of the shining.
But Esperanto uses those compound tenses quite a bit less than English does, so the simple brilas would be more common.
(And in case you tried estas brilas or estas brili, those are simply wrong, like "is shines" or "is shine" would be in English.)