From where does the lowest heaven begin? Is it from the cloud level or higher than that?

In the Arabic language, the term "sky" (السماء) is applied to everything that is elevated, thus it includes clouds and the roof of a house. It is also applied to the lowest heaven (السماء الدنيا), which is one of the seven heavens and is much higher than the clouds. It is common to hear that the lowest heaven is a distance of five hundred years' journey from the Earth, but most of the hadiths narrated concerning this are weak.