Allah, All-High, says,

﴾By the heave and At-Tariq (the knocking star)! And what will make you know what At-Tariq (the knocking star) is?! (It is) the piercing Star.﴿

[LXXXVI; 1-3]

 He, Most Gracious, also says,

﴾By the star when it goes down (or vanishes)!﴿

[LIII; 1]

Interpretation of the verses:

 In fact, interpreters of the Holy Quran reflected on Allah’s Words “the Piercing Star” in the above Verses. Then, they said: “It is a bright star of piercing brightness whose light pierces layers of the Earth’s atmosphere”. But they did not speak about the word At-Tariq (the knocking star).
 As for Allah’s Words, “By the star when it goes down (or vanishes)!”, the star mentioned in this verse differs from a comet that goes down. In fact, Allah speaks about piercing flames in many Quranic Verses. For example, Allah, All-Mighty, says,

﴾Except those who snatch away something by stealing, and they are pursued by a piercing flame.﴿

[XXXVII; 10]

 and,

﴾And we have sought to reach the heaven, but found it filled with stern guards and flaming fires.﴿

[LXXII; 8]

 Therefore, “By the heaven and At-Tariq (the knocking star)! And what will make you know what At-Tariq (the knocking star) is?!” In other words, there is a knocking star, a piercing star, and a star going down (or vanishing). The above Verses, however, have nothing to do with the falling comets that we see everyday.
 Such topic is very complicated, but to simplify things it could be said that when a star becomes gigantic, it shrinks and the internal spaces between its atoms vanish until it becomes very small in size but excessively heavy. In other words, it becomes like an incredibly heavy football in size. Such contracting neutron star weighs more than 50,000 billion tons; and if it were placed on the surface of the Earth, it would pierce it and get through to the other end, just as when you have a semi-solid body on which you put an iron ball that goes immediately into the bottom thereof. This is exactly the piercing star: a neutron star that was compressed until it became as big as a small ball whose weight is equal to that of the whole Earth. When the Earth gets old, it will become as small as an egg, but its weight will remain the same original weight. In other words, it will become like a football as heavy as the Earth. Such is the piercing star as seen by some scientists.
 Moreover, some telescopes have recently received radio waves, in the form of pulse-waves, from these stars. It is as though these stars knock the door of heaven; and the number of pulse-waves increases when the star is still young, while they decrease when it becomes old. In fact, astronomers know the ages of such stars from the number of pulse-waves received by telescopes. In other words, modern astronomy shows that there are different kinds of stars, piercing stars, knocking stars,..etc.
 Allah, All-Mighty, says,

﴾By the heave and At-Tariq (the knocking star)! And what will make you know what At-Tariq (the knocking star) is?!﴿

 This is a Divine Oath, but where is its apodosis?! Allah, All-High, says, “There is no human being but has a protector (and recorder) over him\her.” In other words, all your movements, deeds, words, hopes, intentions, motivations, ambitions, and all that you keep secret from other people, are recorded by Allah, Al-Mighty, either for or against you; and you will be held responsible for all that, since He, Who created the piercing star, the knocking star and the star going down, will call you for an accounting for all you deeds:

﴾By the heave and At-Tariq (the knocking star)! And what will make you know what At-Tariq (the knocking star) is?! (It is) the piercing star. There is no human being but has a protector (and recorder) over him\her.﴿

 No star in the heaven could ever escape Allah’s Knowledge, so could anything ever on the Earth escape His Divine Knowledge?!