Hi,
The Sun is the same size all year 'round, with a diameter of 1,390,000 km.
Over the course of the year the Earth moves a little closer and farther away from the Sun, so the Sun's apparent size changes just a little bit. This does not explain the seasons, however. In fact, during winter in the northern hemisphere the Sun is at its closest to the Earth!

The seasons are caused by the tilt of the Earth as compared to the Sun. In the winter months for Earth's northern hemisphere (December-March) the northern part of the Earth is tipped away from the Sun, so the days are shorter and the Sun's light more spread out. At the same time it is summer in the southern hemisphere.

Six months later the situation is reversed - the southern part of the Earth is tipped away from the Sun and Australia and Argentina are having their winter in July!

Here is a web site describing this,
http://www.windows.ucar.e...ns.html&edu=elem

cheers,
Terry