Behold, I will bring again the shadow of the degrees, which is gone down in the sun dial of Ahaz, ten degrees backward. So the sun returned ten degrees, by which degrees it was gone down.
I will bring again the shadow of the degrees, which is gone down - cause to return. In 2 Kings 20:9; 2 Kings 20:11 the choice is stated to have been given to Hezekiah whether the shadow should go forward or go back ten degree. Hezekiah replied, "It is a light thing (a less decisive miracle) for the shadow to go down (its usual direction) ten degrees: nay, but let it return backward ten degrees;" so Isaiah cried to Yahweh that it should be so, and it was so (cf. Joshua 10:12; Joshua 10:14).
In the sun-dial of Ahaz (Hebrew, bªma`ªlowt (H4609) ... bashemesh (H8121)) - literally, in the degrees in the sun. Herodotus (2: 109) states that the sun-dial, and the division of the day into twelve hours, were invented by the Babylonians, and derived from them by the Egyptians. Ahaz was one, from his connection with Tiglath-pileser, likely to have copied the pattern of an Assyrian sun-dial as he copied the altar at Damascus (2 Kings 16:7; 2 Kings 16:10). "Shadow of the degrees" means the shadow made on the degrees (cf. Psalms 102:11; Psalms 109:23). Josephus thinks these degrees were steps ascending to the palace of Ahaz. The time of day was indicated by the number of steps reached by the shadow. The dial was of such a size and so placed that Hezekiah, when convalescent, could witness the miracle from his chamber. No mention of twelve hours occurs in the Old Testament. Compare Isaiah 38:21-22 with 2 Kings 20:9, where translate, shall this shadow go forward, etc.
The dial was no doubt in sight, probably 'in the middle court' (2 Kings 20:4) - the point where Isaiah turned back to announce God's gracious answers to Hezekiah. Hence, this particular sign was given. The retrogression of the shadow may have been effected by refraction: a cloud denser than the air interposing between the gnomon and dial would cause the phenomenon, which does not take away from the miracle, because God gave him the choice whether the shadow should go forward or back, and regulated the time and place. Bosanquet makes the 14th year of Hezekiah to be 689 BC, the known year of a solar eclipse, to which he ascribes the recession of the shadow. At all events, there is no need for supposing any revolution of the relative positions of the sun and earth, but merely an effect produced on the shadow (2 Kings 20:9-11); that effect was only local, and designed for the satisfaction of Hezekiah, because the Babylonian astronomers and king 'sent to inquire of the wonder that was done in the land' (2 Chronicles 32:31), implying that it had not extended to their country. No mention of any instrument for marking time occurs before this dial of Ahaz, 700 BC The first mention of the "hour" is made by Daniel at Babylon (Daniel 3:6).