Trepidation (astronomy)

The trepidation is a term used in astronomy to describe a variation in the precession of the equinoxes. It is a kind of trembling of the earth's axis, the inaccuracies in the precession caused, so that the progression of the equinox on the ecliptic is sometimes done faster and sometimes slower. The corresponding values ​​are added to the precession or subtract from it.

The trepidation was described and discussed frequently in the Middle Ages. Today, these reports are held for erroneous; the phenomenon is not observed in modern astronomy and is not recognized.

History

Theon of Alexandria is said to have described the theory of trepidation in the 4th century first, where he appeals to unnamed " senior astronomers ." According to Theon they had observed the advance of the Stars by 1 ° in 80 years, but only up to a limit of 8 °, then the process turn around and walk back the same 8 °. The reversal of this movement should be done 128 years before Augustus. Theon but decided against this view and pulled Ptolemy's model in which the precession has a fixed and continuous value.

In the Middle Ages a number of Arab astronomers cite this fluctuation, so the book De motu octavae sphaerae whose Arabic, but lost, Thabit Ibn Qurra original is attributed to what is not undisputed. Thabit - or the author of the book mentioned - worked out a detailed field model, in which he represents the fluctuation of the Präzessionswertes to the change in the obliquity in relationship. Whether the famous astronomer al - Battani accepted the trepidation, is doubtful.

Thabits Trepidationsberechnungen tables of Al- Zarqali were of the Toledans taken over in the 11th century and the phenomenon was discussed by well-known throughout Europe and. Soon, however, the reversal of the motion was rejected as false and assumed a fixed Präzessionswert to the trepidation was then added as a variation, and that this deviation should be / - 9 ° and perform a cycle in 7000 years. This model has been adopted by Alfonso the Wise Alfonsine Tables of Castile and became the adopted in the Middle Ages as the standard theory of trepidation. Georg von Peuerbach took over in 1472 Thabits model and even Copernicus tried once in 1543, building on Thabit to make the trepidation in the account and be connected with the change in the obliquity.

Rejection

Starting mid-13th century, however, there were growing voices that kept this oscillation for mistake and entered for a fixed value of the tropical year and thus the precession. End of the 15th century Regiomontanus turned violently against the view that the heavenly bodies could occasionally perform irregular movements. Finally, Tycho Brahe checked the star data of the Almagest and occurred in the Plant Astronomiae Instauratae Mechanica ( 1595 ) concluded that precession is uniform and the small inaccuracies are attributed to " accidental causes ". From about this time, the trepidation is considered in error, or attributed to observational error or misunderstanding regarding the graduation, and no longer immersed in astronomical observations or calculations.