Earth leans over by 23.4 degrees, and the lean always points the same way in space. When the north leans toward the Sun, its noon sunlight comes in steep, so each patch of ground gets a strong, concentrated beam, and the days are longer. Half a year later the north leans away: the same beam arrives slanted and spreads thin, and the days are shorter. The south gets the opposite.
Not to scale. The ground windows always show noon. Earth is about 147 million km from the Sun in early January and 152 million km in early July, a small difference that does not drive the seasons.
NASA Space Place: What causes the seasons?
NASA: Earth facts
NASA Earth fact sheet