Historical clue formulations

• Arctic lights — 2016-07-24
• Night lights — 2016-04-12
• Free light shows — 2015-02-14
• Night lights — 2013-03-03
• Northern and southern lights — 2011-12-06
• Night lights — 2009-09-02
• Night lights — 2008-05-25
• Meteorological effects — 1997-12-21
• Outdoor light shows — 1996-05-18
• Dawns — 1996-03-22