The longest day of the year in the Northern Hemisphere occurs at the Summer Solstice. On the same day, at the same time, in the Southern Hemisphere, the Winter Solstice brings with it the longest night of the year.
Equinoxes, when day and night are equal, follow the same rule, they occur on the same day and at the same time but in opposite seasons. Spring Equinox in the Northern Hemisphere is mirrored by the Autumn/Fall Equinox in the Southern one and the other way round.
Research historical dates and view a different way of representing the Earth's journey round the Sun.