The human circadian clock entrains to sun time.
Roenneberg
Till
T
Kumar
C Jairaj
CJ
Merrow
Martha
M
D001683:Biological Clocks / Q000502:physiology*; D002940:Circadian Rhythm / Q000502:physiology; D005260:Female; D006801:Humans; D008297:Male; D017440:Photoperiod; D012925:Social Conformity; D013472:Sunlight