Codex hides Hipparco star catalog missing 2,000 years ago

In the middle of the 2nd century BC, the astronomer and mathematician Hipparchus observed the sky from his observatory on the island of Rhodes. He measured the position of the stars with an armillary sphere, which he himself perfected. His goal was to develop the most accurate and complete catalog of stars possible. For each star, he recorded its position using two coordinates (similar to geographic longitude and latitude) and its magnitude (apparent brightness). Thus, with the care of a sage, Hipparchus created the first known map of the night sky. That star map was lost, but not forever.

the stars are moving

While measuring the position of Spica (Alpha Virgo), the brightest star in the constellation Virgo, he realized that it had moved about 2 degrees of latitude from the position recorded by Timocar and other astronomers nearly two centuries earlier. He may have thought it was a measurement error, but the same systematic deviation occurred in other stars such as Regulus (Alpha Leo) in the constellation Leo.

This fact cast doubt on the idea that the stars were fixed points of light on a sphere (later known as the eighth sphere) with the Earth at the center. The explanation that Hipparco found is that the sphere of stars is not fixed, but moves very slowly, as if it were a top. The spinning top’s axis makes an angle with respect to the vertical (tilt of the ecliptic), which Hipparco estimated to be 23°40′, with an error of less than 3′ than at the time, surprisingly accurate.

Vega will be the next star to point north

Without this movement, after a solar or tropical year, the stars would be exactly in the same place, but since they are not, the stars move in a cycle that lasts about 26,000 years.

Let’s think about the North Star. It now points (by the way) roughly north, but it won’t always be that way. In a few millennia, the North will be marked by Vega. This movement is known as the precession of the equinoxes.

Hipparchus came to the conclusion that if we have the position of a star and want to know its past or future position over a long period of time, we must correct for longitude by a little less than 1⁰ per century.

Thus Giparco gave the criteria to be followed so that his catalog could be used at any time in the past and future.

missing directory

Hipparchus’ catalog contained about 850 stars. The problem is that it didn’t survive. In fact, only commentaries on Arato’s astronomical poem have come down to us. But we know from secondary references that Hipparchus invented time and trigonometry.

More than 200 years after Hipparco, another giant of astronomy and mathematics, Claudius Ptolemy, wrote in Alexandria (northern Egypt) one of the most influential books in history, known as the Almagest.

The Almagest includes a catalog of 1022 stars, known as the Ptolemy catalog. Some astronomers suspected that the position of most of them was copied from the Hipparco catalog, and perhaps today we have evidence to answer whether it is correct.

Hidden text

Twins Agnes Smith Lewis and Margaret Dunlop Gibson, biblical scholars, acquired through various purchases made between 1895 and 1906 what is known as Codex Climaci Rescriptus (CCR), containing the Syriac translation of Κλίμαξ θείας ανόδου (“Ladder of the Divine Ascent” or Scala Paradisi) by John Klimakos. And the impressive discovery is that it is a palimpsest, meaning it contains hidden text, in this case biblical texts written in various Aramaic languages.

Recently (October 2022) it was discovered that under this hidden text in Aramaic is another text in Greek. This was revealed in the analysis of multispectral images (Journal of the History of Astronomy). And the surprise was that it partially matches the missing Hipparcos catalog of stars.

The authors of the article combined this data with the little that survived from the catalog at Arathos and compared it with Ptolemy’s catalog. To do this, they took into account that Guiparco used equatorial coordinates and Ptolemy used ecliptic coordinates, and that Guiparco’s catalog reflects the position of the stars in 129 BC, while Ptolemy’s catalog corresponds to 138 BC.

Some results are shown in the table. The right ascension and codeclination of Hipparchus are compared with Ptolemy’s Almagest (Alm).

The differences are very small. Hipparchus’s data appears to be more accurate than Ptolemy’s, and they all seem to have an error of less than 1⁰, which is less than the diameter of two full moons.

To obtain this accuracy, in addition to measuring angles, time must be estimated. At that time, the method of measuring time was very inaccurate, and 1800 years were not enough for the invention of the telescope (1609). The conclusion reached by the authors of the article is that Ptolemy compiled his catalog of stars by combining various sources, including the catalog of Hipparchus, his own observations and, possibly, observations of other authors.

Ptolemy’s catalog was part of his book mathematical syntax (αθηματικὴ Σύνταξις), which was translated from the original Greek into Arabic in the 9th century under the title Al Majisti (Biggest) or Almagest. It was improved in the Arab world, most notably by the Persian astronomer al-Sufi (903–986), or Azofi in the Latinized form. To him and other Arab astronomers we owe the names of many proper-named stars that we know today. It was virtually unknown in Europe until Gerardo de Cremona translated it from Arabic into Latin in Toledo (c. 1175).

J. Guillermo Sanchez Leon, Mathematical Modeling. IUFFyM, University of Salamanca

This article was originally published on The Conversation. Read the original.

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