The term 'Period After Sunset' refers to the three stages of the evening sky: TWILIGHT (8 letters), DUSK (4 letters), and NIGHT (5 letters). TWILIGHT is the period of time after sunset when the sky is still illuminated by the sun, but the sun is below the horizon. DUSK is the period of time between TWILIGHT and NIGHT, when the sky is darkening and the stars are beginning to appear. NIGHT is the period of time after DUSK when the sky is completely dark and the stars are visible.