gökyüzündeki yıldızın yeryüzüne inmiş haline ´´ Tarkan ´´ denir

my attempt

Apparently even the star that is in the sky when it falls to Earth will call the name ´Tarkan´.

Well your translation is partly correct. For which reason you added "apparently even" ?

Translation : The star that is in the sky, is called "Tarkan" when it falls to earth.

If you want to express how wonderful Tarkan is, in English you would say "The star from the sky that has fallen down to earth is called Tarkan." That way you leave the surprise to the end. Otherwise it sounds like someone is shouting "Tarkan" at him on the way down. Actually ´inmek´ is ´to descend´, but ´falling´ sounds better. 

Actually personally I would not say ´from the sky´ because it´s obvious stars are in the sky. But I get that you aim to be poetic here  

I used ´apparently´ because of ´inmiş´ , but ´apparently´ could also be left out.

I used ´even´ because it made the English sentence make more sense to me, but there was nothing in the Turkish sentence that gave a reason to use it.

Thanks for your corrections. The Turkish now makes more sense but I am still a bit puzzled by ´haline´ = into?

Since "inmiş" is a past participle adjective here, you don´t need to use apparently. It defines the state of the star.

Bu çiçekler solmuş= (Apparently) These flowers have faded.

Solmuş çiçekleri attım.=  I threw out the faded flowers.

Bir yıldız dünyaya inmiş= (They say, apparently, I heard) A star fell to earth.

İnmiş yıldız= A fallen star.

hal= situation or state.

Yıldızın inmiş hali= The-fallen on earth-state of a star. (Literal)

You can also shortly say Yıldızın inmişi, it means the same.

Thanks to everybody who participated in this translation 
I haven´t imagined the sentence would be beautiful so far

Thanks for your explanation gugukkusu