Equinox and Solstice

Equinox	Solstice
When day and night are equal	When either day or night is longest or shortest

Date	Feature
21st March	Equal day and night (Vernal Equinox)
21st June	Longest day in Northern hemisphere (Summer Solstice)
23rd September	Equal day and night (Autumnal Equinox)
22nd December	Longest Night in Northern hemisphere (Winter Solstice)