Topic summarySecular trend Expand Summary Extracted from the Wikipedia article Secular variation. References^^^ 234. Bibcode:2001jsrs.meet..231K. ISBN .^^ 120. Bibcode:2001jsrs.meet..119K. ISBN .^ 288. Bibcode:1982A&A...114..278B.^^^ 78. doi:10.1080/03014460150201896. PMID 11201332.^ 189. PMID 10421080.^ 721. doi:10.3109/03014461003727606. PMC 3575631. PMID 20465526.^ . PMID 20696727.^ Wikipedia source