On the discovery of the saros
Abstract
It is believed that in ancient times the most simple and affordable method of predicting eclipses was based on the saros, an approximation to the time period of the eclipse cycle. In many studies techniques for finding the saros through observations of eclipses were considered, but the verification shows failure of these methods. In this paper we propose an experimental method for detecting saros observing lunar eclipses. Saros could be detected by analyzing the repetition periods of partial lunar eclipses with the same phase. This requires regular observations of eclipses over 200div300 years at an average density of at least 30 observations per century. The observer should record the time of the eclipse, its phase and the position of the shadow on the disk of the Moon. The paper proposes an experimental method of determining the duration of draconic and anomalistic months. The knowledge of these values allows to obtain "the saros relation", which Ptolemy assigns to Babylonian astronomy. The determination of the duration of anomalistic month requires the astrolabe or another instrument, which allows to measure the motion of the Moon and time. It is shown that the åxeligmos, the better approximation of the eclipce cycle, can be found experimentally through the observations of the solar eclipses too.
- Publication:
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Bulgarian Astronomical Journal
- Pub Date:
- 2011
- Bibcode:
- 2011BlgAJ..16...72N
- Keywords:
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- saros detection;
- finding the length of the lunar months;
- history of astronomy