Questions have been asked about the proper English spelling of names of astronomical objects, especially as regards capitalisation of such names.
The IAU formally recommends that the initial letters of the names of individual astronomical objects should be printed as capitals (see the IAU Style Manual, Trans. Int. Astron. Union, volume 20B, 1989; Chapter 8, page S30); e.g., Earth, Sun, Moon, etc. "The Earth's equator" and "Earth is a planet in the Solar System" are examples of correct spelling according to these rules.
It is emphasized, however, that language conventions are the responsibility of individual nations or groups of nations. While the IAU is willing to help to achieve a minimum degree of orthographic consistency as regards astronomical terms, it cannot undertake to do so for all languages, nor is it in the power of the IAU to enforce the application of any such conventions.