Equinoxes are days when the duration of day and night are equal, occurring around 21 March and 23 September. Solstices, on the other hand, are the longest and shortest days of the year. The summer solstice (around 21 June) has the longest day in the Northern Hemisphere, while the winter solstice (around 22 December) has the shortest. These changes are caused by the tilt of the Earth’s axis during its yearly journey around the Sun.