Precession
The Vatican library has preserved two ancient manuscripts with estimates of the length of the year. The only ancient scientist listed for two different values is Aristarchus. It is now suspected that these are among the earliest surviving examples of continued fraction expressions. The most obvious interpretations can be computed from the manuscript numbers.
The results are years of 365 + 1/152 days, and 365 − 15/4868 days, representing the sidereal year and the civil, supposedly tropical year.
Both denominators are can be related to Aristarchus, whose summer solstice was 152 years after Meton's and whose Great Year was 4868 years. The difference between the sidereal and tropical years is identical to precession. The former value is accurate within a few seconds. The latter is erroneous by several minutes.
Both are close to the values later used by Hipparchus and Ptolemy, and the precession indicated is almost precisely 1 degree per century, a value which is too low. 1 degree per century precession was used by all later astronomers until the Arabs. The correct value in Aristarchus's time was about 1.38 degrees per century.
Read more about this topic: Aristarchus Of Samos
Famous quotes containing the word precession:
“But how is one to make a scientist understand that there is something unalterably deranged about differential calculus, quantum theory, or the obscene and so inanely liturgical ordeals of the precession of the equinoxes.”
—Antonin Artaud (1896–1948)