Historical clue formulations

• Pertaining to the moon — 2018-11-16
• Relating to the moon — 2016-01-09
• Kind of acid that dissolves gold — 2013-01-19
• Containing element #34 — 2010-07-09
• Kind of acid that dissolves gold — 2005-09-24
• Containing element #34 — 1998-12-13