The Sundial of Ahaz

POSTSCRIPT TO THE SECOND EDITION OF THE HISTORICITY OF BIBLICAL ISRAEL: STUDIES IN 1& 2 SAMUEL (2010)

The Sundial of King Ahaz

by Anthony Lias

In 1985, Professor Kamal Salibi, of the American University of Beirut, wrote a brilliant book entitled The Bible Came from Arabia. Having had unexpected access to a gazetteer of Saudi Arabia published at Riyadh in 1977, his study of it confirmed him in the belief that the place-names of the Hebrew Bible – the actual location of which has always troubled Biblical scholars if taken to apply to what we now call Palestine – fitted perfectly if applied to the region called Asir, situated in West Arabia abutting on the Red Sea.

As someone who has a working knowledge of the original Hebrew vocabulary of the Bible, and who has published three books on place-names myself, I found the hundreds of examples listed by Professor Salibi absolutely convincing. However, I have recently found what I regard as a further powerful proof that Professor Salibi’s argument is correct. To explain why, I must point out that Asir lies (and lay) well within the tropic zone (between 17 and 19 degrees north of the Equator).

Now according to Isaiah 38:7,8, the prophet Isaiah (early eighth century BC) tells King Hezekiah in Jerusalem that ‘the Lord’ will give him a ‘sign’, namely this: “I will bring again the shadow of the degrees, which is gone down in the sun dial of [your father, King] Ahaz, ten degrees backward. So the sun returned ten degrees, by which degrees it was gone down.”

This retrograde motion of a shadow cast by a gnomon (i.e., a sundial pointer) has traditionally been regarded as a ‘miracle’, because at the latitude of the present-day Jerusalem (31 degrees 47 minutes north of the Equator), such a motion would be impossible. However, and I quote a respected figure, the English mathematician/astronomer Thomas Keith (1759-1824): “If a horizontal dial, which shows the hour by the top of the perpendicular gnomon, be made for a place in the torrid zone [i.e. the tropics], whenever the sun’s declination exceeds the latitude of the place, the shadow of the gnomon will go back twice in the day, once in the forenoon and once in the afternoon, and the greater the difference between the latitude and the sun’s declination is, the farther the shadow will go back.” Thomas Keith, A New Treatise On The Use Of The Globes. Revised Edition. London, 1855, pp. 336-7.

Now according to Professor Salibi, the original Jerusalem of Isaiah’s time will not have been in today’s Palestine, but in Asir, and within the torrid zone. Therefore the retrograde shadow on the ‘dial of Ahaz’ will not have been a ‘miracle’, but a fact. And no doubt an experiment could be set up in Asir at the present time to prove this. (N.B: since declination is the angular distance north or south of any heavenly body from the celestial equator, and since the highest possible declination of the sun is 23 degrees 28 minutes, it is plain that during certain months of the year the shadow will go back for every location within Asir.) It is possible that Professor Salibi is unaware of these astronomical details, which I believe are a vindication of his thesis.

The story about the odd behaviour of the sundial of King Ahaz also occurs in 2 Kings, 20:8-12. Here, the story makes it obvious that Isaiah knew that the “shadow of the degrees” on the sundial would go back, and that King Hezekiah did not. My theory is that Isaiah (who is thought by some Biblical scholars to have acquired some astronomical knowledge from the Assyrians), duped Hezekiah into thinking he was witnessing a ‘miracle’, while in reality he was witnessing a genuine phenomenon in the Jerusalem of Asir whose existence is proposed by Professor Salibi, not the later one of Palestine. The fact of the retrograde motion of the shadow of a gnomon within the tropics is independently confirmed and fully explained by Denis Savoie in his book Sundials, Design, Construction and Use (English translation by Bob Mizon, Springer Praxis Publishing, 2009), Appendix F (6), pp.163-4.

I must conclude by saying that Professor Salibi nowhere impugns the religious message of the Hebrew Bible. His thesis, in The Bible Came from Arabia and in the third part of the present work, centres purely on the correct location of places mentioned in the Bible. [Note: for anyone interested, Denis Savoie provides a diagram in Appendix F (6) of his book demonstrating the shadow’s retrograde motion, as well as an explanatory mathematical formula.]