Summer in north, winter in south, as ever in equator

The angle between the Earth's axis and the Earth-Sun line changes throughout the year. The seasons are mostly due to this changes by the axial tilt of the Earth. And mainly affect northern and southern hemispheres, not equator.

Twice a year, at the summer and winter solstice, Earth's axis of rotation makes an angle of about 23. 5 degrees with the direction perpendicular to the ecliptic (the north pole is inclined towards the Sun in June; the south pole is inclined towards the Sun in December). Twice a year, at the spring and fall equinox the two directions are perpendicular.

The oceans, which heat up and cool down slowly, explains why when we receive the most sunshine in solstice (June in North, December in South), this is regarded as the beginning of summer and not its peak. They are still cool from the winter time, and that delays the peak heat by about a month and a half. And similarly, the day of least sunshine in solstice (June in South, December in North), are know as the beginning of winter and not mid-winter day, because the oceans are still heat from the summer time, and that delays the peak cool by about a month and a half