When the sun is high in the sky it's rays are concentrated in a smaller area, hence it's hottest at the equator. The tilt of the earth's axis by 23.5 degrees gives the seasonal differences. Take UK for example today is pretty much midsummer that means the sun is as high as it's going to get and it's rays on us are as concentrated as they are going to get. Six months from now the opposite is true the sun at midday will be the lowest and therefore the rays will be spread out over a much larger area, hence winter weather. The proximity of the sun has very little varyance and very litte effect of temperature variation thoughout the year.