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The Sundial of Ahaz

Atheists love to bring up so-called unscientific problems with the bible. For example, the sundial of Ahaz (2 Kings 20:8-11) is particularly used. But, like I keep telling my atheist friends, knowledge about astronomy and time measuring in the ancient Near-East contribute an accurate understanding of 2 Kings 20:8–11. Here's a sundial with an Aramaean inscription dated to the 6th century b.c. In the ancient Near-East, the sun was a natural time-keeper. Various types of sundials were known to the Egyptians, Assyrians, and Babylonians. Ahaz, who was a pro-Assyrian ruler, had taken over an Assyrian sundial and brought it to Jerusalem. What this sundial exactly looked like was initially unclear. But thanks to the Dead Sea Scrolls, we now have a clear perspective on how such a dial worked. The miracle was that Hezekiah's life was lengthened by 15 years.

1. History of Sundials

The Egyptians had what's called a shadow clock that consisted of a rod of wood with an end-block:

The rod is marked with several points, indicating hours. It was set horizontally by means of a merkhet (plumb-line) suspended against a line scored on the end-block at right angles to the long arm. In the morning, the rod was placed so as to point eastwards. The shadow of the upper part of the end-block was intercepted on the rod. At mid-day, the rod was moved in the opposite direction so as to point westwards. There was another Egyptian sundial discovered during excavations at Gezer:

The object is a piece of carved ivory (5.5 cm long and 1.25 cm wide). On the back is a time-line series. On the front is Merneptah, the pharaoh who ruled at the end of the 13th century b.c. This object is a portable sundial. The sundial must be held in a horizontal position with a small gnomon perpendicular in the hole. But the most fascinating Egyptian sundial is CG 33401:

This one is important with regards to the discussion about the sundial of Ahaz. The length of the object is 35 cm, its height is 10 cm. The object has two steps on one side, and two plain ramps on the other side. There are a total of 12 steps, a number that is equal to the 12 hours of a day. In order to use the sundial, the block is put horizontally where the long sides correspond to the North-South direction, and the short sides correspond to the East-West direction. Thus, this sundial combines three methods of time measuring. There are three receptive areas:

1. horizontal

2. stepped

3. inclined plane

With regards to the use of the steps on the sundial, the horizontal edges of the outer blocks serve as gnomons. At sunrise in the morning, the shadow of the eastern block edge falls onto the leading edge of the topmost step of the stairs, which rises from the east. When the sun climbs, the shadow of the edge moves down the stairs from step to step. At noon, the shadow arrives at the bottom. Then, the western block edge takes over the shadow throwing function, and the shadow climbs up the western steps. The famous Israeli archaeologist Yigael Yadin chose this model as a fine example of what the sundial of Ahaz could have looked like:

He suggested that it was a model of a house. The sundial was incorporated within the structural features of a roof chamber. Thus, here's a striking similarity between the Egyptian model and the reconstruction of the sundial by Yadin. In 2 Kings 20:11, the shadow moves backwards 10 steps. This number is important. In fact, sundials in antiquity were marked with lines for an indication of 6 hours. Thus, 6 steps for 6 morning hours at one side, and 6 steps for 6 noon hours at the other side:

2. Decoding Ahaz's Sundial

Now this is where it gets fascinating. After the discovery of the Dead Sea Scrolls, scholars noticed a variant reading in Isaiah 38:8. This verse was initially read:

I will make the shadow on the steps of the dial of Ahaz that marks the sun go ten steps backwards.

(Isaiah 38:8)

However, there is a crucial word that appears in 1QIsa that offers this reading:

I will make the shadow on the steps of the upper dial of Ahaz that marks the sun go ten steps backwards.

(Isaiah 38:8)

Thus, this has allowed scholars to make a connection with the 1885 French astronomer Camille Flammarion, where he published an article about a special sundial in the Observatory of Juvisy in Paris:

Flammarion had designed and built a sundial to incline the plane in order to show the retro-gradation of the sun's shadow. This was influenced from Pedro Nunes (a Portuguese mathematician in the 1500s), since he was the first scientist that described this phenomenon of retro-gradation and related it to the sundial in 2 Kings 20:8-11. Flammarion fixed a gnomon of 20 cm perpendicular to a horizontal board. When used as a sundial and placed in a North-South direction, the shadow of the gnomon is visible on the northern part of the plane and moves from the left (West) to the right (East).

During his experiment, he inclined the board with the gnomon until the gnomon was in such a position that its shadow was cast on the southern part of the plane. The result was that its zenith fell between the tropic and equator, with the consequence that the sundial (with such an unusual inclination for the geography of Juvisy) showed at solstice in June a retro-gradation of the shadow. At 12:00 pm, a very short shadow was cast exactly on the North-South meridian. The shadow regularly moved in the direction of the East, going up, and became longer and longer. Between 1.50 pm and 2.34 pm the shadow remained stationary. Then, it started to move again, but in the opposite direction, going down, until sunset. The angle of the shadow line at 2.12 pm (with the point where the shadow disappeared from the sundial plane) was 11°. Flammarion also calculated the exact inclination of the gnomon to get a retro-gradation of 10° (according to 2 Kings 20:11), namely 18° north-latitude. For a sundial in Jerusalem at 31° north-latitude, the sundial must be inclined 13°. Thus, the "ten steps" is the number of time units in the ecliptic. When we compare the data of the experiment by Flammarion with the details in 2 Kings 20:8-11, we see some striking similarities:

1. The shadow on Flammarion's sundial moves in two directions. In 2 Kings 20:9, the motions are described by the verbs "go forward ten steps" and "go back ten steps."

2. In the afternoon, the moving shadow on Flammarion's sundial stretched out. Increasing length is a natural property of a shadow between noon and sunset. Meanwhile there is also a progression in motion in a specific direction. In 2 Kings 20:10, we read: "It's an easy thing for a shadow to lengthen ten steps. So let the shadow go backward ten steps."

3. During the experiment by Flammarion, the length of the shadow starts to increase after noon. At the same time it climbed up in the East part of the inclined plane. After a relatively long period of being stationary, the shadow chose the opposite direction and started to come down on the inclined plane. That is what is called a retro-gradation. In 2 Kings 20:11, this crucial moment is marked with two verbs: "who brought the shadow back ten steps after it had gone down the stairway of Ahaz."

4. Flammarion suggested that a manipulated inclined plane is necessary to show the retro-gradation of the shadow. In 2 Kings 20:11 the Hebrew word for "steps" parallels this inclined plane.

5. Flammarion calculated a retro-gradation of 10°. In his view the similarity to the biblical story depends on the supposition that the people in the ancient Near-East were familiar with the same division of a circle in degrees as we have. Evidently, over a century after Flammarion wrote his article, scholars of the ancient Near-East have demonstrated that this is exactly the case of the astronomy in the 1st millenium b.c, where Babylonian astronomers had a systematic recording of celestial phenomena. They had astronomical units called beru. In their calculations, the circumference of the sky became 12 beru, each of which was subdivided into 30 parts. Thus, the Babylonians divided the main circle of the sky into 360 uš. An equals our time and arc degree. In 2 Kings 20:8-11, the Hebrew word for "steps" is a direct equivalent to the Babylonian (or degree). Thus, Hezekiah's extended life can be seen in what he accomplished soon after:

Now the rest of Hezekiah's actions, as well as his glorious deeds, including how he constructed the pool and the conduit to bring water into the city, are recorded in the Book of the Chronicles of the Kings of Judah, are they not?

(2 Kings 20:20)

Archaeologists in 1880 came across an extra-biblical inscription (that dates to 700 b.c., during Hezekiah's reign) cut into the Siloam tunnel that commemorates the accomplishment of building Hezekiah's tunnel that brought water from the Gihon spring directly underground to the pool of Siloam:

The feat was considered remarkable partly because the tunnel was cut by two teams working toward each other from opposite directions and yet meeting accurately in the middle. Here's the translation of the inscription:

[The day of] the breach.


This is the record of how the tunnel was breached.

While [the excavators were wielding] their pick-axes, each man towards his co-worker,

and while there were yet three cubits for the brea[ch,]

a voice [was hea]rd

each man calling to his co-worker;

because there was a cavity in the rock (extending)

from the south to [the north].


So on the day of the breach,

the excavators struck,

each man to meet his co-worker,

pick-axe against pick-[a]xe.


Then the water flowed from the spring to the pool,

a distance of one thousand and two hundred cubits.

One hundred cubits was the height of the rock above the heads of the excavat[ors.]

In conclusion, the details about the properties of the sun's shadow in 2 Kings 20:9–11 are so specific, that we must conclude that the writer of this story had an accurate knowledge about astronomy and time measurement. The phenomena of shadow retro-gradation is real, not unscientific. Thus, another atheistic charge against the biblical narrative bites the dust, yet again.

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