Historical eclipses
Abstract
A historical overview of solar and lunar eclipses is presented in relation to calculating the change in diameter of the sun and the rate of spin of the earth. A 1979 estimate of change in the sun's diameter, based on daily observations since 1750, is calculated to be a 2 arcsec shrinkage, or about .1% per century. Based on solar eclipse timing in 1715 in England, it is concluded that the sun was 0.2 arcsec smaller in 1715 than it is now. Solar eclipse times, when compared with data on the transits of Mercury, reveal a .008 + or - .007 percentage decrease per century, but an 80 year oscillation period with a .025% amplitude may exist. To determine variations in the earth's rotation, only eclipse data from ancient and medieval times are of value. Perhaps the most reliable eclipse data is from observations of the Babylonian eclipse of 136 B.C. Calculations based on this and several other observations reveal an average rate of day lengthening since ancient times to be 1.78 + or - .11 milliseconds per century. To more accurately analyze eclipse observations, the celestial coordinates of the moon must be more precisely estimated.
- Publication:
-
Scientific American
- Pub Date:
- October 1982
- DOI:
- 10.1038/scientificamerican1082-170
- Bibcode:
- 1982SciAm.247d.170S
- Keywords:
-
- Earth Rotation;
- Lunar Eclipses;
- Solar Eclipses;
- Astronomical Coordinates;
- Histories;
- Solar Physics;
- Astronomy