Illa mani istaraqa assamAAa faatbaAAahu shihabun mubeen (surah Hijr: 18)

Tafseer Tafheem-ul-Quran by Syed Abu-al-A'la Maududi

(15:18) except that an eaves-dropper might hear something *11 , but a fiery flame pursues that eaves-dropper. *12

Illaa manis taraqas sam`a fa atba`ahoo shihaabum mubeen

*11) This is the answer to the false claim of the soothsayers, diviners, hermits, conjurers and the like who pretended to receive communications from the Heaven. The Qur'an says that in fact they do not possess any means of obtaining information about unseen things. Satans, however, try to eaves-drop because they are by nature more like angels than human beings, but in reality, they succeed in obtaining very little information about it.
*12) In Arabic the word shihab-i-mubin literally means "fiery flame". In XXXVII: 10, the same thing has been called shihab-i-thaqib ("flame that pierces through darkness"). 'This may or may not necessarily be a "meteor" for it is just possible that it may be some type of rays such as "Cosmic Rays" or even a stronger type which we have not been able to discover as yet. Anyhow if the "fiery flame" that pursues Satans may be taken to be a meteor, a countless number of these can form a fortification around our sphere of the universe. Scientific observations made with the help of the telescope have shown that billions of these meteors are rushing from space in mass of "rainfall" towards the earth's atmosphere. Such a scene was witnessed in an eastern pan of North America on November 13, 1833. This is so strong a fortification that it can prevent Satans from passing through any fortified sphere.
With the help of the above, one can form a mental picture of the "fortified spheres" . Though there is no visible "wall" to keep distinct and separate one sphere from the others, Allah has securely guarded each of these spheres by invisible "walls" against each other. That is why our "planet" has remained safe in spite of the occasional "rainfall" of countless meteors. For as soon as they cross the protective wall of our sphere, they are burnt to ashes. But sometimes a meteorite reaches the earth from outer space as if to warn the dwellers of this planet of the existence of the "power" of the Creator. For instance, the biggest of these weighs 645 pounds and it is obvious from this that if the earth had not been made safe and secure by means of "fortified spheres" the rain of the shooting stars would have utterly annihilated it long long ago. It is these "fortified spheres" which the Qur'an calls "buruj".