Isaiah 20:11 

So Isaiah the prophet cried out to the LORD, and He brought the shadow ten degrees backward, by which it had gone down on the sundial of Ahaz.

Isaiah’s prayer recorded here brought about a miracle as a sign to Hezekiah that God would give him fifteen more years to live (2 Kings 20:5-6).  As it happened, Isaiah gave Hezekiah a choice of miracles; to make a shadow on a set of steps to go forward ten steps (this was the normal direction the shadow would go, but speeded up) or backward ten steps.  Well, Hezekiah chose the most impossible miracle—for the shadow to go backward.  And so Isaiah “cried to the Lord” and the shadow went backward—an incredible miracle wrought through one single faith-filled prayer.

But what was the miracle?  Was the miracle brought about by a means of light refraction, or did God actually turn the earth back upon its axis? The following commentaries may give some ideas.

Commentary by Adam Clark, Adam Clark’s Commentary

We cannot suppose that these ten degrees meant ten hours; there were ten divisions of time on this dial: and perhaps it would not be right to suppose that the sun went ten degrees back in the heavens, or that the earth turned back upon its axis from east to west in a contrary direction to its natural course. But the miracle might be effected by means of refraction, for a ray of light we know can be varied or refracted from a right line by passing through a dense medium; and we know also, by means of the refracting power of the atmosphere, the sun, when near rising and setting, seems to be higher above the horizon than he really is, and, by horizontal refraction, we find that the sun appears above the horizon when he is actually below it, and literally out of sight: therefore, by using dense clouds or vapours, the rays of light in that place might be refracted from their direct course ten, or any other number of degrees; so that the miracle might have been wrought by occasioning this extraordinary refraction, rather than by disturbing the course of the earth, or any other of the celestial bodies.

(from Adam Clarke’s Commentary, Electronic Database. Copyright © 1996, 2003, 2005, 2006 by Biblesoft, Inc. All rights reserved.)

Matthew Henry’s Commentary

He cried unto the Lord by special warrant and direction, and God brought the sun back ten degrees, which appeared to Hezekiah (for the sign was intended for him) by the going back of the shadow upon the dial of Ahaz, which, it is likely, he could see through his chamber-window; and the same was observed upon all other dials, even in Babylon, 2 Chron 32:31. Whether this retrograde motion of the sun was gradual or per saltum—suddenly—whether it went back at the same pace that it used to go forward, which would make the day ten hours longer than usual—or whether it darted back on a sudden, and, after continuing a little while, was restored again to its usual place, so that no change was made in the state of the heavenly bodies (as the learned bishop Patrick thinks)—we are not told; but this work of wonder shows the power of God in heaven as well as on earth, the great notice he takes of prayer, and the great favour he bears to his chosen. The most plausible idolatry of the heathen was theirs that worshipped the sun; yet that was hereby convicted of the most egregious folly and absurdity, for by this it appeared that their god was under the check of the God of Israel. Dr. Lightfoot suggests that the fifteen songs of degrees (Ps. cxx., &c.) might perhaps be so called because selected by Hezekiah to be sung to his stringed instruments (Isa 38:20) in remembrance of the degrees on the dial which the sun went back and the fifteen years added to his life; and he observes how much of these psalms is applicable to Jerusalem’s distress and deliverance and Hezekiah’s sickness and recovery.

(from Matthew Henry’s Commentary on the Whole Bible, PC Study Bible Formatted Electronic Database Copyright © 2006 by Biblesoft, Inc. All Rights reserved.)