Question: When did WIlliam Herschel started to serve as President of the Royal Astronomical Society?
Paraphrase: What was the date when William Herschel began his term as the President of the Royal Astronomical Society?
SPARQL (Wikidata): SELECT ?value WHERE { wd:Q14277 p:P39 ?s . ?s ps:P39 wd:Q24357183 . ?s pq:P580 ?value}