A prominent feature in the non-dipolar part of the secular variation is a " westward drift " at a rate of about 0.2 degrees per year.
12.
The term secular variation is used wherever time series are applicable in economics, operations research, biological anthropology, astronomy ( particularly celestial mechanics ) such as VSOP ( planets ) etc.
13.
The last crossing of the zero line was shown to have occurred during the 1947 1948 sunspot maximum, making that epoch of importance to statistical methods designed to remove this secular variation from ionospheric studies.
14.
However, this hypothesis, which was initially proposed by Joseph Larmor in 1919, has been modified due to extensive studies of magnetic secular variation, paleomagnetism ( including polarity reversals ), seismology, and the solar system's abundance of elements.
15.
These massive evolved stars are unstable due to their high luminosity and position above the instability strip, and they exhibit slow but sometimes large photometric and spectroscopic changes due to high mass loss and occasional larger eruptions, combined with secular variation on an observable timescale.
