Here's a link to a story about an extremely interesting development from the professional work of Dr. Bradley Schaefer, a professor of astronomy and astrophysics at Louisiana State University in the US.

Entitled "Ancient Astronomers were No Fools" by Camille Carlisle, the article (published in Sky & Telescope) explains a finding presented by Professor Schaefer at a recent meeting of the American Astronomical Society, in which he argues that ancient astronomers including Ptolemy and Hipparchus appear to have corrected for "extinction" -- the dimming of a star seen closer to the horizon, which is caused by the fact that an observer on earth must look through a greater thickness of earth's atmosphere when observing a star lower in the sky and closer to the horizon -- when compiling their star catalogs.

As the article explains,
Extinction happens because starlight has to pass through Earth’s atmosphere in order to reach us. But the effect isn’t uniform: if you spend time stargazing you’ve probably noticed that a star high up in the sky’s dome looks brighter than it does as it slides toward the horizon. That’s because light coming to us from near the horizon passes through more atmosphere than if it shines straight down from overhead. (The Sun looks redder at sunset and sunrise for the same reason.)
A diagram in the linked article illustrates that an observer looking to the heavens at a 90° angle to the ground he is standing on (looking straight up) only has to look through "one air mass" (the thickness of the atmosphere). However, the same observer looking out towards the horizon at an object situated only 10° up from the horizon will be looking through 5.6 air masses.

Professor Schaefer has done innovative research in the past related to the work of the ancient astronomer Hipparchus (c. 190 BC - c. 120 BC), and is widely known for his analysis of the constellations depicted on the Farnese Globe (in another extremely important piece of detective work, Professor Schaefer concludes that the constellations depicted on the globe are accurate enough in their placement to indicate consultation by the sculptor with the star catalog a learned astronomer, and that their placement is consistent with the epoch of Hipparchus, meaning that this sculpture preserves vital information about the lost star catalog of Hipparchus; this assertion has been contested).

His current work also resulted from an investigation related to Hipparchus: Professor Schaefer was trying to answer the age-old question of whether the later astronomer Ptolemy (c. AD 90 - c. AD 168) derived some of his star information found in his Almagest from the earlier work of Hipparchus.

As Camille Carlisle explains in her Sky & Telescope description of Schaefer's latest analysis:
It was the Almagest that Schaefer began with — but his goal wasn’t to determine if astronomers in olden days accounted for extinction. He wanted to use the brightnesses reported in it to decide a long-standing debate over who wrote the catalog in the first place, Hipparchus of Rhodes (circa 150 BC) or Ptolemy of Alexandria (circa AD 150).

Some researchers have looked at the positions reported for the Almagest’s 1,000-plus stars to try to distinguish between the theories, but the differences aren’t conclusive. So Schaefer decided to try using atmospheric extinction to crack the case. Rhodes is at 36° north latitude and Alexandria at 31.2° N, which means the same stars will appear lower in the sky (and therefore dimmer) in Rhodes than they will in Alexandria. The star Canopus, for instance, is by modern calculations the second brightest star in the sky, after Sirius. Canopus should have looked 4th or 5th magnitude to Hipparchus but 2nd magnitude to Ptolemy, Schaefer says. (Astronomers’ magnitude system is also ancient, based on Hipparchus’s work: a magnitude 1 star is 2.5 times brighter than a star of magnitude 2.) By comparing the Almagest brightnesses against modern magnitudes — which are extrapolated to how they would appear outside the atmosphere — Schaefer should have been able to tell by the growing difference between the two values where the observer was. But he soon discovered a problem.
Carlisle explains that Schaefer's comparisons of magnitude indicate that the ancients were compensating for the atmospheric phenomenon of extinction. Professor Schaefer says: "You would expect that as you look further south the Almagest magnitudes would start … going up and up and up. But when you look and see the real data, you see that they are not going up and up and up. Somehow somebody corrected the Almagest magnitudes for extinction. It’s the only way."

Since the ancients apparently never wrote about the phenomenon of extinction (at least, not in any texts that survived or that were cited by authors of texts that survived), historians had not previously credited precise understanding of extinction to mankind prior to the eighteenth century. Professor Schaefer explains the surprise caused by the indication that the ancients may have actually possessed a fairly advanced understanding of this phenomenon: “it’s rather surprising that [the ancients] did a sophisticated and pretty accurate correction for something they don’t talk about and no one ever knew they knew about.”

The work of Hipparchus and Ptolemy is extremely important in the story of mankind's understanding of another extremely important celestial phenomenon, the phenomenon of precession. Hipparchus is widely credited with being the first astronomer to deduce what was going on, and Ptolemy also discusses the phenomenon in his Almagest (probably based on the work of Hipparchus). The importance of the work of Hipparchus and Ptolemy is discussed extensively in the Mathisen Corollary book, as is the phenomenon of precession itself (along with extensive diagrams and explanation to enable all readers to feel confident in understanding precession for themselves).

In fact, the debate over whether Ptolemy based his star catalog on the earlier work of Hipparchus is touched on in passing on pages 74-75 of the paperback version of the Mathisen Corollary, in which I explain that:
Most of the works of Hipparchus are no longer extant. The only surviving text penned by Hipparchus himself is a critical commentary on the astronomy contained in the poem Phaenomena by Aratus of Soli, who died about fifty years before Hipparchus was born. [. . .] From his commentary on the poem of Aratus, we can deduce much about Hipparchus' understanding of the heavens, which he brought to bear on the work of Aratus. Even further, we can observe the impact of his thought in references to his work in surviving texts, especially in Ptolemy's "Great Treatise," the Almagest.

Otto von Neugebauer (1899 - 1990) [was] one of the most important modern scholars of the story of astronomy from Babylon to the time of Isaac Newton [. . .]. Neugebauer, following the work of Irish astronomer Robert Stawell Boll (1840 - 1913), believed that Hipparchus' catalog contained the positions of no more than 850 individual stars (fewer than the 1,022 stars of Ptolemy's catalog in the Almagest), and that based on the surviving details in the commentary [of Hipparchus] on Aratus, Ptolemy's star location details were arrived at independently from those of Hipparchus, rather than being simple derivations of them as is commonly believed (285). Neugebauer also provides evidence that Hipparchus was in possession of and familiar with the extensive records of the earlier Bablyonian astronomers, who had compiled copious arithmetical tables of the intervals between various celestial events. 74-75.
My discussion of Hipparchus and Ptolemy centers around the extensive evidence (provided throughout my book, based upon evidence noted by other analysts including de Santillana and von Dechend, Graham Hancock, Martin Doutré, and Jane Sellers, as well as some evidence I have not seen discussed elsewhere) that ancient civilizations understood precession thousands of years before Hipparchus and Ptolemy, and to a greater degree of precision than either Hipparchus or Ptolemy apparently achieved.

Based upon the evidence, it is clear that the ancient Sumerians, Babylonians, and Egyptians must have had an extremely accurate and sophisticated knowledge of the stars and their behavior, which is a requirement for figuring out precession. It is therefore quite likely that the knowledge of the phenomenon of extinction also predated Hipparchus and Ptolemy by tens of centuries as well, although I do not have direct evidence for this logical deduction (note however the comment quoted above that Neugebauer found evidence that Hipparchus possessed extensive ancient Bablyonian astronomical texts and records).

As for Professor Schaefer's surprise that the ancients display a pretty accurate and sophisticated understanding of a concept that "they don’t talk about and no one ever knew they knew about," the question of why certain astronomical knowledge (including the understanding of precession) was not explicitly declared in ancient texts is a fascinating topic. It is one that has been examined previously in this blog, such as in the post entitled "If the ancients really knew so much, why didn't they just come out and say it?"

As John Anthony West (whose thoughts on the subject are discussed in that post) has written in his outstanding treatise Serpent in the Sky, much of the scientific knowledge supposedly "discovered" by the ancient Greeks was actually secret knowledge that they got from the ancient Egyptians. The Egyptians were just better at keeping a secret. He writes, "But perhaps unfortunately, Egypt was also much better at keeping her secrets than the loud-mouthed Greeks -- so very good that Egyptologists refuse to believe she possessed them" (36).

We hasten to point out that Mr. West is no doubt referring here to the ancient Greeks, and that his remarks are not to be taken as applicable to any specific group today.

Professor Schaefer's discovery, that the ancients apparently understood extinction to a high degree, is yet another piece of evidence in a growing pile of evidence indicating that ancient civilizations possessed an extremely advanced science long before conventional history as taught for the past several decades has been prepared to admit. His important work also opens up a host of other issues about ancient astronomical knowledge, and invites us to ask how much older this knowledge might be.

We should all be grateful to Professor Schaefer for his ability to use astronomy to provide important new perspectives on human history, and his willingness to advance hypotheses which go against the current conventional thinking.