This darkening of the sun will take place in the full light of midday. And as its golden rays enlightening the face of nature rejoice both man and beast, so the sudden withdrawal of its light will cause sorrow and distress to the whole of creation And this all the more, because the moon will cease to shine, and her gentle, peaceful light will no longer illuminate the shades of night. All the stars also which bespangle the firmament and cast a glimmering to earth, will disappear from their accustomed place. This awful darkness will strike such alarm and anguish to the heart of all living creatures, both men and brutes, that the mourning and lamentation will be universal.

With the wail of distress ascending from the dwellers upon earth, the howls of the evil spirits in the air will mingle in hideous concert, for they will perceive from these signs that the Day of Judgment is at hand; they know that they will soon have to appear before the rigorous tribunal of God; they know they will be cast down to Hell for all eternity. Hence their fury, their rage, and frantic raving.

This is what Christ means when He says: "The powers of Heaven shall be moved and the stars shall fall from Heaven."

Christ Himself tells us this will be so: "Upon earth will be distress of nations by reason of the confusion of the roaring of the sea and of the waves; men withering away for fear, and expectation of what shall come upon the whole world" And in another place He says: "There shall be then great tribulation, such as hath not been from the beginning of the world until now, neither shall be. And unless those days had been shortened, no flesh should be saved"

When this lamentation has lasted for a time, the God of justice will put an end to their misery, and all that is beneath the firmament of Heaven shall be destroyed by fire. For fire will fall down from Heaven, and ignite everything with which it comes in contact. In many places also flames will spring up out of the ground, and terrify unhappy mortals to such an extent that they will not know how to escape from them. Some will seek shelter in cellars and caverns, others will immerse themselves in rivers and lakes. The devouring flames will spread so fast that the forests will be set on fire, and the towns and villages will be included in the destruction. At length the whole earth will be on fire and a general conflagration will ensue, such as never has been seen or heard of. The heat of the raging flames will be so intense that the stones and rocks will melt, and the sea and all waters upon the earth will boil and hiss.

All men then living, every beast upon the land and every fish in the sea will be destroyed in this universal conflagration. Thus the whole world will be brought to a terrible end, and everything on this earth will be either consumed or purified by the fire. After this has happened, the appearance of the earth will be completely changed.
http://catholictradition.org/Classics/4last-things2a.htm

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