Circadian Rhythms. We are awake during the day and asleep at night...mostly.
Image credits Leonardine36 / Pixabay.
Tired parents carry a baby who is awake at night. The baby looks cheerful and
Effects of caffeine on the human circadian clock - MRC Laboratory of Molecular Biology
Wake Clipart #1
Sheep - Wake Forest Demon Deacons - Team Colors - College Football Clip Art