The substantial achievements in astronomy that Nidhal Guessoum refers to occurred earlier than the 'golden age' of Arab astronomy from the ninth to the sixteenth century AD (Nature 498, 161–164; 2013).

Astronomy developed between the fourth century BC and the first century AD, but especially in the third century BC. It matured from tables of observations, from which only a few general patterns were recognized (the saros eclipse cycles, for example), into a sound understanding of the Solar System. This included good estimates for the size of Earth and the sizes of the Sun and the Moon, as well as their distances, and the discovery of the precession of the equinoxes. More importantly, a majestic mathematical construction allowed the prediction of the positions of all of the major bodies visible in the sky, with a precision close to the best available with observation (10 minutes of arc). These achievements were products of Alexandrian astronomy, mostly by Greeks living in Egypt, and were summarized by the writer Claudius Ptolemy.

Good intentions motivate Guessoum's examples of Arab excellence in astronomy, such as columns (gnomons) that were used to measure time (common in the earlier, scientifically illiterate Roman Empire) and of sailors using the arc of the Moon to indicate the east–west line (a technique already known for a couple of millennia). But glorifying these as achievements shows a lack of respect for today's students in the Arab world. Furthermore, the stated strictly religious motivations of Arab astronomy, absent in Alexandrian times, may sound like a justification for religious control of science — still a danger in many countries.

To their credit, Arab astronomers recognized the value of Alexandrian astronomy, and even developed it in some details. They saved the old astronomy, which, through Nicolaus Copernicus, led to the ignition of modern science.