On or about June 22, the first day of summer in the Northern Hemisphere, the northern tip of Earth’s axis is inclined toward the sun at an angle of 23.5 degrees from a line perpendicular to the plane of the ecliptic. This is the summer solstice in the Northern Hemisphere.
On or about December 22, the first day of winter in the Northern Hemisphere, the southern tip of Earth’s axis is inclined toward the sun at an angle of 23.5 degrees from a line perpendicular to the plane of the ecliptic. This is the summer solstice in the Southern Hemisphere.